yellowstone science · mapping yellowstone lake predator and prey at fishing bridge. as director of...

Yellowstone ScienceA quarterly publication devoted to the natural and cultural resources

Volume 11 Number 2

110˚35'W 110˚30'W 110˚25'W 110˚20'W 110˚15'W

110˚35'W110˚30'W 110˚25'W 110˚20'W 110˚15'W

44˚20'N

44˚25'N

44˚30'N

44˚20'N

44˚25'N

44˚30'N

PelicanRoost

SedgeBay

Mary Bay

TurbidLake

Indian Pond

PelicanValley

Yellowstone River

Bridge Bay

GullPoint

SandPoint

RockPoint

Pumice Point

StevensonIsland

Dot Island

FrankIsland

BreezePoint

WolfPoint

EagleBay

Delusion Lake

Flat Mountain Arm

ElkPoint

ThePromontory

PloverPoint

South Arm

SoutheastArm

West Thumbbasin

Elliott'scrater

inflated plain

the fissures

outletgraben

Mary Baycrater

ParkPoint

BiscuitBasin

AlderLake

YellowstoneRiver

StormPoint

Steamboat Point

northern basin

east central basin

west central basin

Lake Butte

DuckLake

EvilTwincrater

spirefield

TheYS Interview: Lisa MorganMapping Yellowstone Lake

Predator and Prey at Fishing Bridge

As Director of the National Park Service from 1940–1951, Newton B. Drury spent a great deal of his tenure fending off a constant flow of demands that the national parks be plundered for the resources they could contribute to wartime and post-war necessity. In that last year of his directorship, in the midst of the Korean War and a growing with the Cold War, he penned thesewords as an introduction to Freeman Tilden’s The National Parks: What They Mean to You and Me.

Now, as these words are written, with prospects of a third world warlooming up, with the need all the greater for a haven from the tensions ofmodern life, for an environment of quiet and peace and serenity, a book likeTilden's leads people's thoughts into channels upon which proper mentalbalance and perhaps even national sanity may depend. So much the moreimportant, therefore, to cherish these crown jewels among the lands of thenation, to keep them unsullied and intact, to conserve them, not for com-mercial use of their resources but because of their value in ministering tothe human mind and spirit. In war or in peace the national parks have theirproper and proportionate place in the life of America. These lands are lessthan one percent of our area. Surely we are not so poor that we need todestroy them, or so rich that we can afford to lose them.

“In War or in Peace”

EditorRoger J. Anderson

[email protected]

Assistant Editor and DesignAlice K. Wondrak

Assistant EditorsTami BlackfordVirginia Warner

Technical Assistanceand PrintingArtcraft, Inc.

Bozeman, Montana

Special Color Issue!

Yellowstone ScienceA quarterly publication devoted to the natural and cultural resources

ContentsScience with Eyes Wide Open 2YS talks with USGS geologist Lisa Morgan about science, discovery, and the joys of life in the caldera

The Floor of Yellowstone Lake is Anything but Quiet! 14New discoveries from high-resolution sonar imaging, seismic reflection profiling, and submersible studies show there’s a lot more going on down there than we may have thought.by Lisa A. Morgan, Pat Shanks, Dave Lovalvo, Kenneth Pierce, Gregory Lee, Michael Webring, William Stephenson, Samuel Johnson, Carol Finn, Boris Schulze, and Stephen Harlan

7th Biennial Scientific Conference Announcement 31

Yellowstone Nature Notes: Predator and Prey at Fishing Bridge 32In prose and on film, Paul Schullery captures a little-seen phenomenon: the aesthetics of survival in the world of a trout.

by Paul Schullery

News and Notes 40Gray wolf downlisted • Bison operations commence outside North Entrance • Spring bear emergence reminder • Winter use FSEIS released • YCR 10th anniversary

Around the Park 43Springtime in Yellowstone.

Volume 11 Number 2 Spring 2003

Cover: New high-resolution bathymetricrelief map of Yellowstone Lake, acquired bymultibeam sonar imaging and seismic map-ping, surrounded by colored geologic map ofthe area around Yellowstone Lake. Courtesy USGS.

Left: 1883 woodblock engraving of Yellow-stone Lake, probably produced for publica-tion purposes and handcolored at a latertime.

Above: A trout rises to the surface of the Yel-lowstone River.

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Yellowstone Science is published quarterly. Submissions are welcome from all investigators con-ducting formal research in the Yellowstone area. To submit proposals for articles, to subscribe to

Yellowstone Science, or to send a letter to the editor, please write to the following address:Editor, Yellowstone Science, P.O. Box 168, Yellowstone National Park, WY 82190.

You may also email: [email protected].

Support for Yellowstone Science is provided by the Yellowstone Association, anon-profit educational organization dedicated to serving the park and its visitors.

For more information about the association, including membership, or to donate tothe production of Yellowstone Science, write to: Yellowstone Association, P.O. Box

117, Yellowstone National Park, WY 82190.

The opinions expressed in Yellowstone Science are the authors’ and may not reflecteither National Park Service policy or the views of the

Yellowstone Center for Resources.

Copyright © 2003, Yellowstone Association for Natural Science, History & Education.Yellowstone Science is printed on recycled paper with a linseed oil-based ink.

2 Yellowstone Science

YS (Yellowstone Science): Lisa, whenwe first met, you described your back-ground as a little bit different than that ofmost geologists, in that you started out asa fine arts major. Could you tell us a littlebit more about that, and how it affects howyou go about looking at your work today?

LM (Lisa Morgan): I did start out as afine arts major. Along the way, I took amineralogy and optical crystallographycourse in my pursuit of fine arts because Iknew we’d be studying color and light the-

ory, which I always thought was prettyinteresting. My hope was that the coursewould enable me to have a better under-standing of the color spectrum and howlight works. So I took that class and had totake prerequisites in physical and histori-cal geology and before I knew it, I waskind of hooked into geology. And I lovegeology. One of the things I think fine artsbrings to geology is the ability or interestto look in detail at things, and to see thingsthat you might not normally look for. Likewhen you’re drawing, how you’re going

to draw something is going to be very dif-ferent than if you just took a photograph ofit, and you’re going to consider the rela-tionships somewhat differently whenyou’re drawing something than if you’rejust going to document it with a photo-graph. So I think fine arts brings this abil-ity to see or look.

I guess I would describe myself as afield geologist who studies the geologyand geophysical characteristics of volcanicterrains, and I think having a fine arts per-spective gives me another set of tools with

Science with ‘Eyes Wide Open’An interview with geologist Lisa Morgan

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A research geologist with the U.S. Geological Survey, Dr. Lisa Morgan has devoted 23 years to studying the geologyand geophysics of volcanic terrains. Since 1999, she has been working in Yellowstone, mapping and interpreting thefloor of Yellowstone Lake and its associated potential geologic hazards—an undertaking that was completed last sum-mer. We felt that an achievement of this magnitude warranted extensive coverage in Yellowstone Science, and areexcited to publish its results. In 2002, YS editor Roger Anderson had the opportunity to discuss this project and otherissues with Lisa at her Boulder, Colorado, home. We are pleased to include this interview, which provides interestinginsights into the mapping process as well as into her personal approach to the science of geology.

Dave Lovalvo, Lisa Morgan, and Pat Shanks launch a remotely-operated vehicle (ROV) into Yellowstone Lake. TheROV aids in ground-truthing recent bathymetric and aeromagnetic mapping of the lake floor conducted by the USGS.

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which to understand the Earth. Myapproach is to do science “with eyes wideopen.” And that’s where I see the connec-tion with art, because when you take on acanvas, you start with a specific drawing orpainting in mind but as you work on it, thepainting begins to shape itself. You don’tstart a painting saying, “I know exactlywhat colors I’m going to use. I knowexactly what I’m going to draw or painthere.” You don’t know exactly what thefinal results will be. And I think youshouldn’t, either, with science. When youstart out on a proposal, certainly you haveideas of what you want to look at, how toproceed, certain goals, objectives; but youneed to make sure thatyou keep your optionsopen enough so that youdon’t miss anything thatmight be necessary inyour final interpretationof what you’ve seen, orwhat you’ve recorded. SoI think a lot of our work inYellowstone Lake hasbeen a perfect example ofgoing into an area usingtechniques we really had-n’t used before, using abroad group of differentindividuals from differentdisciplines all bringingdifferent skills to the sametable, allowing us to iden-tify things we didn’tknow were there. Andallowing us to come toconclusions that we didnot know we were going to come to whenwe started the original study.

YS: Right. So if you had a pre-set par-adigm, and you found something else andit didn’t fit into that, you don’t go with thepreconceived notion of what you’re goingto find. That’s what you mean, “eyes wideopen.”

LM: Exactly. And a lot of times, you’llfind, in science, and maybe in other things,too, people want preferred outcomes. Theyalready know where they’re going to getto, and they have their product that they’resupposed to produce, and that’s whatthey’re going to do. And I think it’s impor-

tant that we get out our products that wepromised we’ll get out, but I think it’s alsoimportant, as natural scientists, to makesure we’re not missing something. Sowhile I have models in mind, I get reallyfrustrated when I’m in the field and some-body tells me, “well, this model tells me itcan’t be this.” I don’t care what your modeltells you. Just look at the relationship. For-get any model, and just look at that, studywhat you’re seeing in that relationship, andthen see how that compares with yourmodel. But sometimes, people go in theresaying “well, it’s got to be something otherthan this.”

YS: Is your approach unusual, do youthink, among scientists?

LM: I don’t know; probably not. Ithink there are a lot who don’t come to thetable already working within a prescribedmodel. But I’m sure there’d be people whowould disagree with me on that, too. Inmy experience, when I meet with people inthe field and we’re looking at differentthings, some people already have kind ofan idea what it has to be. But I think it’sokay to say “well, I don’t know what it is.”I think nature is a continual puzzle formost of us. And there are a lot of things westill don’t know or understand, whichkeeps us going.

A great example from our 2001 field-work is, we discovered charcoal and treemolds in the Lava Creek Tuff. We haveactual pieces of charcoal present in someof the tree molds, which was surprisingbecause these pyroclastic flows are typi-cally erupted from very large calderas atpretty incredible speeds, and emplaced atvery high temperatures, probably on theorder of 800-850ºC.

YS: And it’s unusual, because in thatheat you would expect everything wouldbe consumed.

LM: That’s correct. At this location,we were close to an areainterpreted as an eruptivevent for the Yellowstonecaldera, and there’s a lotof evidence to suggestthat there may have beensome water involved inthis particular part of theemplacement of thedeposit, which probablydecreased the tempera-ture.

Tree molds are com-mon in basaltic lavaflows, such as those inHawaii and at Craters ofthe Moon, Idaho, butvery little study has beendone on the preservationof tree molds in rhyolitepyroclastic flow deposits,like the Lava Creek Tuff.Tree molds and charcoal

are somewhat rare occurrences in thesetypes of environments. To find charcoal inthis deposit, preserved charcoal, is aninteresting discovery, and contributes towhat we know about the climate 640,000years ago when the Yellowstone calderaerupted.

YS: Where in the park did you findthis?

LM: It’s in the vicinity of Fern Lake,close to the topographic edge of thecaldera.

YS: Now, if I was out with you lastsummer on the trail, walking through that

Lisa points out a "twig mold" in the 0.64-Ma Lava Creek Tuff. A modern twighas been placed above "twig mold" for comparison purposes.

COURTESY LISA MORGAN


part of Yellowstone, what would you seethat I wouldn’t necessarily see that wouldmake you want to stop and take a closerlook? What are you seeing in the land-scape that makes you want to investigatethis particular spot, and then how do you,in all of Yellowstone, get to that place andmake that kind of find?

LM: Here’s exactly what happened. Ithad been raining on and off that day. PatShanks and I were in one work group andSteve Harlan, Lydia Sanz, and Beth Erlandwere in another work group, and Pat and Iwere discussing where to go next. It wasstarting to rain again, and we had to crossthe creek. I had taken my backpack off andwas putting my raingear on. I’m constant-ly, just always looking at everything. Andas I was tying my shoelaces, I put my eyeson this little piece, that was just a surfacepiece, probably no more than a couple cen-timeters long. It had a very fine rim, orcoating of silica on it, and then inside ofthat was this twig impression—this treemold. And it was very, very tiny. So it wasa fluke. Just like a lot of things in science.

And so I saw that little thing, but thenit started pouring. And so we skedaddled.We only had the next day left, and I justhad this feeling that I had to go back to thissite and have a closer look at the impres-sion and site in general. Anyway, we wentback up there, and I said, “look at this. It is

a tree mold.” And I just happened to pickthis piece up, and there was all this char-coal, and also pine needles and impres-sions.

And Pat said, “well maybe that got inthere through some kind of later fluvialaction, or maybe there was just naturalplating forsome reason,and you hadsome flood-ing, and yougot the pineneedles inthere,” and so then I went to another, and Isaid, “what appears as the characteristicfeature of this particular site and deposit isthe unusual nature of the platyness of theunit and that’s a reflection of its content oforganic matter.” I said to Pat, “I think theplatyness and the organic matter in the ign-imibrite are part of the original deposit. I’llbet you a beer that when I go over to thatplaty zone and that platy zone and that oneand all of these zones will be full of char-coal and have impressions of pine nee-dles.” He said ok to the bet. So I went andlooked at all these different places in therock exposure, and each one was full ofcharcoal and pine needle impressions. SoPat ended up buying me a beer after our13-mile trek out of the backcountry. Butyou see, the beauty of having people workwith you with different backgrounds, is

that everyone brings a somewhat differentperspective and set of experiences. It’smuch better than just having your ownideas and self to bounce concepts off. It’salways good to have somebody who willchallenge one’s thinking. It keeps youhonest and keeps you thinking.

Later, whenI told KenPierce [of theUSGS] aboutthe tree moldsand pine needleimpressions

found in the Lava Creek Tuff, his reactionwas, “Oh my gosh! That is so cool,”because in the field of paleoclimatology, adebate exists about whether the Yellow-stone caldera erupted during a glacial orinterglacial period. And he said, “I thinkyou’ve got key evidence now for showingthe Yellowstone caldera erupted during aninterglacial period. It has to be, to have allthose pine needles and trees.” So that waskind of cool.

YS: It’s amazing. Without that collab-oration, without people looking at theresource from different perspectives, youmight not have made that really criticalconnection.

LM: That’s right. So anyway, back tothe eyes wide open, that allowed us to seethat. A lot of the discoveries on Yellow-stone Lake have happened the same way.Before we started our West Thumb sur-vey, the current thinking was that mostfeatures in the lake are from the last glacialperiod since it’s pretty well establishedthat over a kilometer of ice was over thelake 20,000 years ago. That certainly hadto have had a pretty profound influence inshaping the lake. But what we’ve found isthat it certainly is not the only, nor was itthe most important, influence on shapingthe floor of the lake.

People had previously mapped Steven-son, Frank, and Dot Islands as being gla-cial remnants. And, certainly, if you wentout there today, the rocks exposed on theislands are glacial tills. But what we’vefound with our high-resolution, aeromag-netic map, (based on the magnetic surveydone with an airplane), in tandem with oursonar and seismic surveys of the lake, was

Lisa Morgan and fellow USGS geologist Ken Pierce kick back on the Mary Bay explosionbreccia deposit.

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I guess one of the things our projecthas exemplified is that not any oneperson has all the answers.

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that the majority of the underwater topog-raphy, or the bathymetry of the lake, isreally due to rhyolitic lava flows that wereemplaced some time after the Yellowstonecaldera formed. Now, in retrospect, I think,“Oh, well, that’s so obvious,” becausewhat do you see around there? It’s all lavaflows. And why would you think that all ofa sudden, just because you have a lake, thelava flows wouldn’t be in there? But it wasa big, major discovery in mapping WestThumb.

We’ve found that discontinuities, oranomalies, on the aeromagnetic map coin-cide with the mapped extent of the rhy-olitic lava flows on land, and you can fol-low those out into the lake. Our detailed

new bathymetricmaps of the lakefloor show thatmany of the mag-netic anomaliescoincide with hum-mocky areas of highrelief. We interpretthese as rhyoliticlava flows, and sug-gest that Frank, Dot,and StevensonIslands are on theselarge lava flows. Sothe glacial tills thatoccur on Dot,Frank, and Steven-son Islands are real-ly just mantlingmuch larger fea-tures; rhyolite lavaflows underlie theislands and shape

the lake bottom. And if we had held on tothe old model, we may have been blind toseeing that those flows were there.

YS: Explain to the uninitiated aboutthese aeromagnetic maps you’re talkingabout. What’s the process, and what doesit generate?

LM: Basically, we attach a magne-tometer onto a fixed-wing airplane, andthen this airplane flies over the topographyat a constant elevation above the terrain. In

this particular survey, the plane flew lines400 meters apart on an east-west orienta-tion, in a continuous pattern over the park.The magnetometer measures the totalmagnetic intensity of the Earth’s field, andthat can be broken down into two maincomponents, the magnetic remanence andmagnetic susceptibility. Generally, themagnetic remanence records the signaturefrom the earth’s magnetic field that therock acquired at the time of its formation.

Volcanic rocks are emplaced at tem-peratures above the Curie temperature,which refers to the temperature belowwhich a mineral of a specific compositionbecomes magnetic. Minerals in the vol-canic deposit acquire the magnetization ofthe Earth’s field at the time that that rockwas emplaced and give the rock its specif-ic magnetic remanence direction. Theearth’s magnetic field changes its polarityover time so that volcanic rocks erupted atdifferent times will have different and spe-

cific magnetic rema-nence directions. Withmagnetic intensity, we

also measure the mag-netic susceptibility,which is basically ameasurement of howsusceptible that rock isto an ambient magneticfield.

Susceptibility valuescan vary depending on arange of conditions. Inthe case of Yellowstone,what seems to be themajor variable for sus-ceptibility is howhydrothermally-alteredthose rocks are. Whenyour rock is extremely

hydrothermally altered, the magnetic min-erals in that rock are also altered, andbecome much less magnetic. A lot of timeswhat we’re seeing is titanomagnetitesgoing to hematite or ilmenite. Hematite isnonmagnetic and ilmenite is weakly mag-netic, so the magnetic susceptibility of therock goes to almost nothing. Most of therocks we’re looking at in much of the Yel-lowstone Lake area were erupted in thelast 700,000 years, after the last big rever-sal in the Earth’s magnetic field. So whenwe’re looking at the total magnetic inten-

Dave Lovalvo at the controls of the ROV hedesigned and built. What the ROV sees isvisible on the computer monitor seen at thefar right. A second monitor (not seen) dis-plays water temperature readings and a sec-ond picture of the lake floor. This photo wastaken inside the cabin of the NPS’s Cutthroat,which is dedicated for research purposes.

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sity of the rocks in Yellowstone Lake, thevariable that is changing most is the mag-netic susceptibility, which in this casereflects the amount of hydrothermal alter-ation in the rock.

In many places in Yellowstone,hydrothermal alteration is associated withthermal springs. Hot waters come up alongconduits and alter the rockand magnetic mineralsthrough which they’re flow-ing. The hydrothermal alter-ation of the rock lowers themagnetic susceptibility.When you look at the newlyacquired total magneticintensity map of Yellow-stone, you see a map thathas areas with magnetichighs and areas with mag-netic lows. In some areas,we can use this map as aguide for where we mightexpect hydrothermal alter-ation to be present; in otherareas, we can use the map toidentify faults and otherstructures.

YS: So this is how yougo about looking at the park,and looking at the rocks, andtrying to piece together allof the stories that they haveto tell?

LM: I guess one of thethings our project really hasexemplified is that not anyone person has all theanswers. I think if we wentinto Yellowstone Lake justdoing a bathymetric map,we’d have a pretty appeal-ing map, but the bathymetrycombined with the totalmagnetic intensity map andthe seismic reflection pro-files enable our producing amore powerful product witha higher level of confidence. Add to thisthe data we collect with the submersibleROV (remotely operated vehicle), and thedata set is pretty complete. The ROV iswonderful, because it allows us to ground-truth what we have imaged with the multi-

beam and seismic sonar systems. TheROV is a one-meter-by-one-and-a-halfmeter vehicle, built and piloted by DaveLovalvo of Eastern Oceanics. It’s attachedto the boat by a 200-meter tether, whichallows continuous observation of the lakefloor. At its front is a pan-and-tilt videocamera, which records images from the

floor of the lake. On the front is alsomounted a 35-mm camera. The videocamera is on at all times so we can reallysee the floor of the lake. That aids us in oursampling, and the still lifes are wonderfulto see. The ROV is great also because it’s

able to measure temperatures and collectsolid and fluid samples of hydrothermalvents, lake water, and sinter. Later thesecan be taken to the laboratory and be ana-lyzed for mineralogy, chemical and iso-topic composition, and microscopic struc-tures.

So the ROV allows us to observe andsample what we haveimaged bathymetrically andseismically. And that’s beencritical. The multi-beammapping of YellowstoneLake presented challengesseldom found elsewhere.Thermal vents so dominantin different parts of the lakecause frequent changes inthe temperature structure ofthe lake, and therefore, thesound velocity profile. Inour first year (1999), whenwe mapped the northernpart of the lake, we identi-fied several features, whichturned out to be artifacts inthe data. So we collectedmore frequent sound veloc-ity profiles than one wouldin a non-thermal environ-ment. Having the ROV asour eyes and hands on thebottom of the lake allowedus to confirm the bathymet-ric images.

While we’re very confi-dent of our imaged data, theability to sample fluids andsolids, measure tempera-tures, and photographicallydocument the lake flooradds an incredibly valuablecomponent to our lake stud-ies. In 2000, we went withthe ROV to linear featureswest of Stevenson Islandthat were imaged in 1999.As a result, we have photo-graphic evidence that thefeatures are fissures with hot

water coming up along open cracks in softmud and precipitating iron and manganeseoxides on the fissure walls. The fissuresare parallel to and part of the Eagle Bayfault zone, which is a young fault systemmapped south of the lake at Eagle Bay.

Remotely-operated vehicle (ROV). The large orange balls are flotationunits. Water samples are drawn through the large tube mounted on theleft. A thermometer/camera is visible in the mid-foreground, directlyabove the basket used for scooping up sediment samples from the lakefloor.

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This system probably continues northwardof the fissures to the young graben north ofStevenson Island.

YS: Does that continue with the faultnear the Lake Hotel?

LM: That’s right. The Lake Hotel isnear the fault. Soagain, our mappingof the Lake hasenabled us to lookat its geology inmore detail and ina broader context.And YellowstoneLake isn’t an easylake at all to figureout, or to work on.You think of mostlakes as beingquiet, calm, andgood passiverecorders of thelocal climate andgeologic process-es. But Yellow-stone Lake is any-thing but quiet.

YS: Which ofthose technolo-gies—the aero-magnetic survey,the ROV, thebathymetry—played a role in determiningthe caldera boundary under the water?

LM: I would say the two most impor-tant ones were probably the recentlyacquired aeromagnetic data and thebathymetry. Much discussion has been hadabout where to draw the caldera boundarythrough the lake. Using both of these datasets, we trace the topographic margin ofthe Yellowstone caldera right throughFrank Island.

YS: Weren’t you going back and forth?You were describing once about how youwere out on the boat, and you were takingmeasurements on what you thought wasinside the caldera, outside the caldera.

LM: Yeah. Once we got the bathyme-try, it coincided perfectly with where we

had put the boundary based on the magdata. And so that was so cool, and then wewere able to take the ROV, and we couldsee the caldera margin in the lake. It lookslike a bunch of discontinuous, bathtub-shaped troughs, kind of marching throughthe central basin. The multiple data setsgive the same conclusion, so that one can

say with much better confidence that thisis definitely where the caldera margin is.

YS: I’m going to just back up for a fewminutes, and get us back to how we beganthe discussion, from the fine arts to geolo-gy, to this philosophy of looking at yourwork with your eyes wide open, and askyou to elaborate a little more about yourbackground. Once you found geology, tellus a bit about your schooling, where youwent, your degrees…

LM: I went to the University of Mis-souri at Kansas City, and at that time itwas just a small undergraduate geologydepartment, and I had great mentoring andopportunities there. That was key. I got ajob in the department, starting probably inmy junior year. I was a lab technicianthere. After I graduated, I worked for a

short time in a jewelry store with the inten-tion of eventually becoming a gemologist,but then I got a job that paid twice as muchwith an oil company. I stayed with the oilcompany about 10 months but left toreturn to the University to teach labs forintroductory geology classes and work asa technician in their analytical lab. I then

moved to Coloradoand got my Mas-ter’s degree at theUniversity of Col-orado at Boulder,focusing onigneous petrologyand volcanology.

I then had agreat opportunityin 1980 to work atMt. St. Helens, andon August 7, I wit-nessed one of itssmaller pyroclas-tic-flow-producingeruptions from aplane about a kilo-meter or two awayfrom the vent. Thateruption was sig-nificant because itcreated quite agood eruptivecloud, and in thatcloud you couldsee part of it col-

lapsing and forming pyroclastic flows onthe flanks of the volcano. While the pyro-clastic flow was moving, one could seehow this flow concentrated in areas oflower topography, such as valleys comingoff of St. Helens. I could see fine ash beingblown out of the front of the deposit. AndI just decided then I wanted to focus onhow pyroclastic flows are emplaced. Beingat St. Helens gave me a great opportunityto see what volcanologists do. And so inthe following year I decided to go for myPh.D., and study with George P. L. Walk-er, at the University of Hawaii, whose pri-mary focus at the time was ash deposits,their facies, and emplacement processes.

YS: When did you first work in Yel-lowstone on geology?

LM: I started coming to Yellowstone

Lisa Morgan in 1980, doing field work for her master's degree. She is sitting next to the baseof the 6.65 million year old Blacktail Creek Tuff, the oldest caldera-forming ignimbrite fromthe Heise volcanic field. The Heise volcanic field (4-7 Ma), on the eastern Snake River Plain,is similar in origin to the Yellowstone Plateau volcanic field, and immediately preceded itsformation in space and time along the volcanic track of the Yellowstone hot spot.

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probably 1979–1980, because I was work-ing on the Snake River Plain and therewere many similarities between the Qua-ternary rhyolites in Yellowstone and theslightly older rhyolites on the Snake RiverPlain. I was working on my Master’s the-sis; its focus was a stratigraphic study of athick section of pyroclastic flow depositsexposed on the northern margin of the

eastern Snake River Plain. As we knownow, but didn’t know then, the Snake RiverPlain is a whole bunch of old Yellowstone-like calderas and volcanic fields. I was firstformally assigned to Yellowstone in 1995,but, over the previous 15 years, I used themore complete exposures and caldera-related features present in Yellowstone asa way to better understand what I waslooking at on the Snake River Plain, whereexposures of rhyolites are mostly limitedto the margins of the Plain. Today, mostYellowstone-like features in the SnakeRiver Plain are covered by Quaternary orvery recent, young basalts. Eventually, likethe eastern Snake River Plain, Yellowstonewill be much lower in elevation than it isnow and also will be covered by basalts.

YS: Explain to me how in the futureYellowstone will be much lower.

LM: Currently scientists can image

molten, very hot material underneath Yel-lowstone, and, in general, this mass of hotmaterial causes the general Yellowstonearea to be topographically higher than thesurrounding areas. Over time, if the Yel-lowstone caldera is similar to earlier Qua-ternary calderas in the Yellowstone Plateauvolcanic field, which we have every reasonto believe is true, basaltic lavas will erupt,

eventually fill the caldera floor, and con-ceal the Yellowstone caldera. What is nowmolten magma will eventually crystallizeand become denser, and thus less buoyant.The overall topographic elevation will sub-side from today’s current elevation. Withcontinued southwest movement of theNorth American plate over the thermal dis-turbance that causes Yellowstone today, anarea northeast of the present-day locationof the Yellowstone Plateau will becomeelevated and rise above Yellowstone. Infact, we can already witness this. Thisprocess of uplift followed by volcanismhas been occurring for the past 16 millionyears along the Snake River Plain startingin southwest Idaho. So today, Yellowstoneis anywhere from 1 to 2 kilometers abovethe Snake River Plain, depending on whereone takes measurements.

YS: When did you begin to work withthe USGS?

LM: In 1977, when I moved to Col-orado.

YS: What was your first job withthem?

LM: It was great. I made a Denverdump map. My job was basically compil-ing a map showing where all the landfillsin the greater Denver area were. And thatmap transformed a lot of how I live my lifetoday, and how I look at what our respon-sibilities are as citizens on Earth. TheUSGS had been asked to do this becausethere had been a series of accidents asso-ciated with former landfills. Some acci-dents were due to spontaneous combus-tion of methane that caused some fires,some explosions. I think a couple of peo-ple were either seriously burnt or killed.Also, housing developments constructedon top of these landfills were developingcracked foundations and walls due to dif-ferential subsidence in the landfills. It wasimperative that a comprehensive look betaken at where these landfills were locat-ed, so that city and county planners couldmake more informed choices of where toallow or deny development. I was blownaway by how many dumps there were, andwhat went into these landfills. So muchof it could be recycled, reused, and not putin there in the first place. And since then,I’d say starting in like the mid-80s, ourfamily has probably put out no more thanmaybe three to four bags of garbage in ayear.

YS: Really.

LM: (Smiling) Yeah. We don’t sub-scribe to the landfill too much; they shouldbe kept to a minimum. There’s a berm outin our yard where we put all the inertbuilding material that would have gone tothe landfill, but that we took care of here.Right now I’m on the Boulder CountyRecycling and Composting Authority, andour goal as a county is to divert, by 2005,our solid waste levels from 1994 by 50%.And I think we’re going to achieve thatgoal. In the City of Boulder, our single-family residential diversion rate is at 49%,so we have almost met our 2005 goal sev-eral years ahead of schedule. However, inthe arenas of commercial and industrial

Ground-truthing with the ROV means visiting several sites each day, requiring that the crewdrop and haul anchor numerous times. Here, Lisa displays some hydrothermally-altered claythat came up with the anchor.

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waste and for multi-family units, our diver-sion rates are only about 15-20% from1994 levels, so these are areas where westill need to focus and significantlyincrease our diversion rates. And we’repushing the stakes up higher and trying toget to 80% diversion from 1994 levels. It’san informal goal for the City of Boulder.Last year, the city council passed a newordinance, referred to as the “pay-as-you-throw” ordinance, that really forced indi-viduals to pay the true cost of their trash.This has resulted in major behaviorchanges and a significant increase in ourlevel of recycling and reuse. People cando it, but you have to have the infrastruc-ture in place, like curbside pickup andmixed paper and commingled containers.So that’s a long story, but that was my firstjob with the USGS.

YS: What’s your current job?

LM: Now I work at Yellowstone. Thisyear I’m assigned to Yellowstone 100% ofmy time. We’ve finished the map of Yel-lowstone Lake, and are working on variousaspects of the postglacial hydrothermalexplosion craters and deposits that areprobably the most immediate serious haz-ard in the park. The last very largehydrothermal explosion event that weknow of was 3,000 years ago at IndianPond. Of course, in recent years smallerhydrothermal explosion events haveoccurred in the Norris basin, Biscuit Basin(1915), West Thumb, and Potts thermalbasins and elsewhere in the park. Sothey’re very much a current feature ofactivity that Yellowstone National Parkhas to deal with. I’ve also been working onthe physical characteristics of the LavaCreek tuff and its emplacement, and how itrelates to the formation of the Yellowstonecaldera. And then there’s the mapping ofYellowstone Lake that’s basically con-sumed me for the past four years.

YS: Was your work in Yellowstone onthe caldera what ultimately brought you todo the extensive work on YellowstoneLake? What intrigued you about Yellow-stone Lake that has led you to do so muchwork there?

LM: Yes, originally I came to Yellow-

stone to work on the Lava Creek Tuff,which erupted from the Yellowstonecaldera, to better understand its formation.But I also came to do the ground-truth forthe aeromagnetic survey we flew in 1996.With Steve Harlan, I’ve collected orientedcore-samples from most of the Quaternaryand Tertiary volcanic rocks in the park forour magnetic studies.

As far as the lake, if you think of all ofthe geologic maps in Yellowstone Nation-al Park, the one place that didn’t have ageologic map was the Lake. What reallygot me into Yellowstone Lake was myinterest in the hydrothermal explosiondeposits. We were already engaged indetailed studies of the deposits from MaryBay, Indian Pond, and Turbid Lake onland, and I was very interested in trying tounderstand the eruption of Mary Bay. Inour 1999 survey, one of our big discover-ies was what we are now calling Elliott’scrater, which is an 800-meter widehydrothermal explosion crater complex onthe floor of the lake in the northern basin.

YS: The work you and others havedone in recent years has really kind of rev-olutionized the way we look at the lake. Ifwe could look at the bottom of Yellow-stone Lake, from the mapping you’vedone, what would it look like?

LM: If you took all the water out, you

would have a very hummocky terrain.You’d have a terrain very similar to whatyou see in the Central Plateau now, wherethere are a lot of very steep-sided, hum-mocky terrain dominated by rhyolitic lavaflows. And these lava flows would have acap of glacial and lacustrine sediments.Intermixed with this hummocky terrainwould be a whole series of hydrothermalvent fields throughout the lake. Thehydrothermal vents are associated with thelava flows, generally near their edges. Andso, one of the largest thermal fields in Yel-lowstone National Park is on the floor ofthe lake. It’s pretty magical exploring theseareas. On top of this very hot area, we’veseen a lot of fissures, which are linearcracks in the lake bottom. I can’t think ofan area on land in Yellowstone where youhave big open fissures like these. Maybe insome of the thermal fields, but some of thelake-bottom fissures that were discoveredin 1999 and 2001, in the northern and cen-tral lake, extend for several kilometers.Another feature one would see are the very

large lake-bottom explosion craters, simi-lar to Turbid Lake and Indian Pond onland.

YS: Duck Lake, too?

LM: Yes, Duck Lake is a large explo-sion crater immediately west of West

Spring 2003 9

The sun rises on Yellowstone Lake. The lake’s unpredictable summer weather makes it bestto get an early start.

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Thumb basin. You may have noticed asteep slope west of the West ThumbGeyser Basin. This is an apron of debristhat was ejected during the hydrothermalexplosion of Duck Lake. A morphologicaldifference between the large explosioncraters on land and those on the floor of thelake is the radial apron of debris around thecraters we see on land. In the lake, a well-defined rim around the central crater isabsent. Most of this difference may have todo with the medium in which the eruptionoccurred.

YS: And the vents, and the spires…

LM: And then you’d have spires, orconical features, that are anywhere fromone meter all the way up to about 8 metershigh, over in Bridge Bay. We think Monu-ment Geyser Basin, near the northwesternedge of the Yellowstone caldera, may beanalogous in its origin to Bridge Bay. Andthen just north of Stevenson Island, you’dalso see a large young graben, which is adown-dropped block with bounding faults.About two meters of displacement is on

the west side, and about six meters of dis-placement on the east side. And we founda lot more vents in West Thumb basin thanwe had previously thought.

YS: Where else did you find them?

LM: They’re in the south-central partof the West Thumb basin as well as in thenorthern part of the basin, along the edgesof rhyolitic lava flows.

YS: How about Mary Bay?

LM: Mary Bay is a huge crater com-

plex. It’s a whole series of smaller cratersinside a much larger main crater. One ofthe things that we need to get a better han-dle on is that not all of these craters areproduced by explosions. We think someof these craters may also be produced bydissolution collapse. As you know, thelake has areas of very high heat flow,which came out of research by previousworkers such as Paul Morgan, Bob Smith,and Dave Blackwell. The high heat flow is

responsible for the occurrence of hundredsof hot springs on the lake floor. Thehydrothermal fluids are very acidic andchange the composition of the rocksaround them. And so in the lake, most ofthe rock composition originally was rhyo-lite, which is mostly quartz, silica,feldspar, and plagioclase. Feldspars andplagioclase are altered easily by this acidicfluid and are changed into clays. And thenthese hydrothermal minerals precipitatein this system forming a kind of imperme-able seal. At some point all the vents andfissures that were conduits for these fluidsseal up. The acidic hydrothermal fluids

and gases continue to do their work, whichis to alter the substrata, and at some time,either these things explode and there’s acatastrophic failure of that sealant, orthere’s collapse of all this material under-neath. Now, I don’t think we understandhow we distinguish these two at this point,or how we can forecast what’s going tohappen. But I certainly hope some of ourseismic profiles give us more insight intoour ability to look at the structural integri-


“We got bubbles!” Although GPS units are the crew’s primary mode of navigation, patches of bubbles rising to the lake’s surface can act ashydrothermal landmarks as those aboard the Cutthroat search for the exact spot to launch the ROV.

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Spring 2003 11

ty of the rocks underneath the lake. Or thelake sediments.

YS: Of all the findings you’ve madeon the lake, what surprised you the most,would you say?

LM: I don’t know, I mean, the wholething has been like a discovery a day. Andso it’s been really exciting, and has openednew ways to examine multiple activeprocesses, and has been quite fun alongthe way. You never are quite surewhat you’re going to find. Iguess I’d say the biggest surprisewas either the fact that the rhy-olitic lava flows played such animportant role in shaping thefloor of the lake and controllingthe location of the hydrothermalvents, or that the caldera marginshowed up so clearly in thebathymetry and coincided withareas of magnetic lows. Thatwas really cool.

To see the caldera margin isreally fascinating. And thehydrothermal craters are justphenomenal. When you seethese large structures, you knowa very complex process isinvolved, because not only doyou have 800- to 2000-meterdiameter structures, but through-out the floor of these structureshydrothermal processes areactive and one can see and sam-ple active hydrothermal vents.And so you think “well, wherecan you go on land where youcould see something like that?”and so in the summer of 2001,we started mapping Indian Pondand Duck Lake, and right now we onlyhave the seismic reflection profiles. Butthat should give us a lot of indication ofwhat’s going on in those lakes. I think it’simportant for the park, from a public safe-ty perspective, to understand activityoccurring in the hydrothermal explosioncrater lakes as well, because like geology,nothing’s static. We know from our recon-naissance seismic surveys in Duck Lakeand Indian Pond that active hydrothermalvents are on their floors.

Also, large landslide deposits, includ-

ing a couple large detachment blocks, havecome off the eastern, and to a lesser extent,western shores of Yellowstone Lake.These are kind of hummocky, but not aspronounced as the lava flows. The causesof these landslides and their effects on Yel-lowstone Lake are an important topic forfurther study.

YS: How much of the lake bottom hasbeen surveyed?

LM: We finished surveying the Southand Southeast Arms in 2002, so the bathy-metric mapping of the lake is completed!About 75–80% of the lake is within theYellowstone caldera. Outside the calderaare the South and Southeast Arms, whichare fault-bounded valleys whose shape hasbeen enhanced significantly by glacialprocesses. Much of the floor of the South-east Arm is characterized with a hum-mocky bathymetry with many depressionsreflective of kettle and glacial meltwaterterrain seen elsewhere in Yellowstone and

Grand Teton National Parks. After melt-ing, voids left by the ice were later partial-ly filled with slumped sediment leavinglarge, tens of meters wide, irregularly-shaped depressions.

YS: Earlier, you talked a little bit aboutthe interplay between geology and bio-logy. Could you elaborate?

LM: As you know, lake trout havebeen discovered in Yellowstone Lake, and

the native cutthroat trout is preyto the lake trout. Pat Shanks hasbeen working on the geochem-istry of the sublacustrinehydrothermal fluids, looking attoxic elements that we knowexist in other hydrothermal sys-tems, including mercury, anti-mony, and thallium. Crus-taceans are a primary foodsource for cutthroat trout, so thequestion arose, what kind oftransmission is there from thevents to the lowest life formsthat we could identify, on upthrough the food chain to thecutthroat trout and up to the laketrout? So he started looking atmercury content of fish muscle,vital organs, and skin. And hefound a higher than normal con-centration in both the lake andcutthroat trout.

The park is interested inidentifying areas in the lakewhere lake trout spawn. Laketrout are anadromous, meaningthey stay within the lake theirentire lives. Cutthroat are poto-modromous meaning theyspawn in the streams that feed

into the lake during the early summer andlater they come back and live in the lake.When they are spawning in the streams,they become potential food sources formany species, some threatened or endan-gered such as grizzly bears, bald eagles,otters, and osprey. If the cutthroat disap-peared, the lake trout, which never leavethe lake, would not take their place in theecosystem. It’s a major resource issue forthe park and understanding where laketrout spawn is key to controlling theirnumbers and to the ultimate survival of the

Even graduate students need a break every now and then.

COURTESY LISA MORGAN

cutthroat trout. Our understanding when we started

this study is that lake trout like to spawn ingravelly areas. So we thought if we couldidentify gravelly areas in the lake withhigh-resolution bathymetry and seismicprofiles, we could lead the biologists to thespawning areas for the lake trout. As itturns out, we’re findingthat the lake trout hangout in other areas in addi-tion to the deep gravellyareas. The cutthroat troutlike to hang out in warm,thermal shallow areas,which have been called“cutthroat jacuzzis.” ThePark Service has foundlake trout coming intosome of these jacuzzi ventareas to prey on the cut-throat trout.

So biology has amajor role in the Yellow-stone Lake studies. Forone, identifying whateffects toxic metals pres-ent in hydrothermal fluidshave on lake water chem-istry and how they affectits ecosystem is impor-tant. Secondly, how thoseeffects are rippled up intothe larger animals outsidethe lake is equally impor-tant. Chuck Schwartz,Charles Robbins, and theInteragency Grizzly BearStudy Team working withBob Rye and Pat Shanksrecently have analyzedhair from four bears in thepark. Two of those bearscome from areas veryclose to the lake, two are from fartheraway. The two bears close to the lake haveelevated levels of mercury in their hairwhereas those bears not living near thelake do not. So in this example, it seems astrong relationship exists between thegeology of the lake and grizzly bear andcutthroat trout ecology.

That’s one issue. Another is the spiresand how they formed. Scanning electronmicroscopic (SEM) images show that thespires are composed of a variety of

diatoms and silicified bacteria. And thatwas a big surprise. We had supposed thatthe hot silica-enriched waters hitting thecold lake water interface would precipi-tate amorphous silica without biologicinvolvement. When we went and looked atthe spires under the SEM, sure enough,our compositions were for pure silica but

the material was primarily silicified bacte-ria with diatoms. And so there’s somethinghappening on the floor of the lake that isvery much involved in some of the verybasic life forms that operate very closelywith development of these hydrothermalvents. So it’s kind of interesting to see thefull circle come back.

YS: What work remains to be done?What questions still need to be asked whenyou look at the lake?

LM: Well, for starters, I think the lake,the park, and science would be well servedby doing a series of cores on selected sitesin the lake. That would shed a lot of infor-mation about the timing of differentevents: timing of seismic events, ofhydrothermal explosion events, of land-slides. Cores collected in specific areas

would give informationabout what triggers thelandslides. Were they trig-gered seismically, or werethey triggered from thehydrothermal explosionevents? Or from some-thing else? Potentially,data from selected corescould tell us somethingabout evolution of the dif-ferent hydrothermal sys-tems. Not just thehydrothermal vents, butalso the large hydrother-mal explosion complexes.I would also like to knowmore about the climate ofYellowstone in the last12,000 years. Certainly,coring into the lake wouldgive us a clearer idea ofwhat the climate was likeduring these differentevents, and what kind ofinfluences there mighthave been.

We need to have a bet-ter understanding of theissue between large-scalecollapse of hydrothermal-ly altered features versuslarge-scale hydrothermalexplosions and associatedhazards. We need toimprove our understand-

ing of doming activity on the lake floor.Do these doming events always end up inan explosion, or do they end up in a col-lapse, or do some of them not do anything?I think that’s important. Are the domes thathave been identified in our surveys poten-tial precursors to hydrothermal explo-sions? If so, how do we monitor these fea-tures? Also the young and active grabennorth of Stevenson Island should be mon-itored, especially given this structure’sproximity to the Lake Hotel. Putting CO2


Lisa Morgan’s field notebook.

and SO2 sensors next to vents in the domesis important. I would like to see more workdone using LIDAR (light detection andranging) outside the lake. Ken Pierce andRay Watts’s initial work with this tech-nique in association with some other peo-ple shows that Storm Point may actuallybe an inflated structure.And so we might want toexamine that pretty close-ly. Much work remainsand, to summarize, thiswould include mapping,coring and associatedstudies, assessing thepotential hazards, andidentifying the instru-mentation needed formonitoring.

YS: How about in thebroader context of thecaldera outside the lake?

LM: Well, I wouldhope that we get a betterunderstanding of thehydrothermal explosionpotential inside thecaldera. Most, if not all ofthe hydrothermal explo-sions that we’ve identi-fied occur inside thecaldera. So that needs tobe assessed. I think it’salso very important tounderstand the “heavybreathing” aspect of theYellowstone caldera.And again, Ken Piercehas shown a lot of inter-esting data that looks atthe coincidence betweenuplift and subsidence ofthe Yellowstone caldera with relationshipto timing of some of these hydrothermalexplosion events. So I think that’s veryimportant. From my perspective, probablyone of the greatest and most likely poten-tial hazards in the park is the potential fora hydrothermal explosion. In terms ofscale, it’s not going to affect North Amer-ica, but it potentially could affect thepark’s facilities, infrastructure, and visi-tors. And when you think of the transientpopulation that goes through Yellowstone

on a daily basis, it’s very much an urbanpopulation. If you took the number of vis-itors that you have coming to Yellowstoneon an annual basis and divided it by thedays, you basically have the city of Boul-der, Colorado in Yellowstone every day.The problem with your population is it’s

moving all the time. But the park prettymuch controls where it moves. And so it’simportant that the park have a better under-standing of where these hazards mayoccur.

Clearly, assessment of other potentialhazards, such as volcanic and seismicevents, are big items and will be includedin the ongoing hazard assessment con-ducted under the auspices of the recentlyestablished Yellowstone Volcano Obser-vatory, a joint effort between the USGS,

the University of Utah, and the NationalPark Service (Yellowstone National Park).

A lot of work remains that will contin-ue to build on previous investigators’research and findings. We still have a farway to go in improving our understandingof the connections between geology and

biology, and how thebiota react to differentgeologic events in thepark.

YS: Finally, pleasedescribe some of yourmemorable momentsworking in the park.

LM: It’s been a chal-lenging and rewardingresearch experience towork in Yellowstone. It’sbeen so much fun towork in Yellowstone.And it’s just been kind ofa dream, like the summerwhen we did our back-packing trip up to FernLake, it was like, “I can’thandle any more discov-eries!” (Laughing) Justthe number of discover-ies we’ve been able tomake through the courseof our research has beenphenomenal, so I feelvery lucky to have hadthis opportunity. It’s alsobeen pretty awesome towork in this environmentwhere the sight of a griz-zly makes one realizewhat a unique, special,and still wild place Yel-lowstone is. To under-

stand the geologic framework in whichbears and other species inhabit allows us amore comprehensive understanding ofwhy certain species live where they do andthe challenges they face in their environ-ments in order to survive and what wemight do to enable their survival. For sev-eral of these species, Yellowstone is theirlast outpost, so it’s up to those of us whowork in the park to make sure that they’reprotected.

Spring 2003 13

LISA MORGAN

Yellowstone Lake.


The Anna.

Evolution of mapping Yellowstone Lake, 1871-2002

Henry W. Elliott, 1871 Hayden survey Hague report, 1896

Kaplinski, 1991 U.S. Geological SurveyNational Park Service

1999-2002

“The lake was very rough. The waves coming in were equal to waves on the sea coast. Elliott says they were able to take but three soundings, it being rough all the time.

The wind once was so strong that the mast was broken off and carried away. The boat rode splendidly."

Albert Peale, mineralogist, US Geological Survey Hayden survey, August 14, 1871

Spring 2003 15

HISTORY OF MAPPING YELLOWSTONE

LAKE

Yellowstone Lake is the largest high-altitude lake in North America, with anelevation of 2357 m (7731 feet) and a sur-face area of 341 km2 (Plate 1, inset). Over141 rivers and streams flow into the lake.The Yellowstone River, which enters at thesouth end of the Southeast Arm, dominatesthe inflow of water and sediment. The onlyoutlet from the lake is at Fishing Bridge,where the Yellowstone River flows northand discharges 2000–9000 cubic feet/sec-ond. The earliest attempt to produce adetailed map of the shoreline and bathym-etry of Yellowstone Lake occurred duringthe 1871 U.S. Geological Survey expedi-tion, when Ferdinand V. Hayden led 28scientists, scouts, and cooks in a survey ofwhat is now Yellowstone National Park.The sheer effort expended by this group,under the most primitive of working con-ditions, is impressive on its own, but espe-cially when considered in tandem with themany accomplishments of the survey. Aprimary goal of the party was “mak(ing) amost thorough survey of [YellowstoneLake],” reflecting Hayden’s general inter-est in watersheds and river drainagebasins.

A 4.5 × 11-foot oak boat with a woolenblanket sail was used to map Yellowstone

Lake. Mapping took 24 days and includedapproximately 300 lead-sink soundings.Navigation was carried out using a pris-matic compass. Albert Peale, the survey’smineralogist, described the process in hisjournal (see box).

The survey mapped a shoreline of 130miles; the most recently mapped shorelinegives the perimeter of Yellowstone Lake to

be 141 miles (227 km). Over 40 sound-ings were taken along the north and westshores, the deepest being around 300 feet.The survey estimated the deepest part ofthe lake would be farther east and no deep-er than 500 feet. This depth range is com-parable to what we know today; the deep-est point in Yellowstone Lake is due east ofStevenson Island (Plate 3B) at 131 m (430feet) deep. In addition, the Hayden surveyidentified the long NE/SW-trending trough

crossing the central basin. Plate 1 showsthe map of Yellowstone Lake as drawn byHenry Elliott of the Hayden survey. Themap not only shows a detailed topograph-ical sketch of the Yellowstone Lake shore-line but many of the points where sound-ings were taken for the survey.

A second map of Yellowstone Lake,published in 1896, incorporated elements

of the original 1871 Elliott map from theHayden expedition. While no mention ismade in the official USGS report of addi-tional mapping or modifications made tothe Elliott Yellowstone Lake map, or evenof any additional work on YellowstoneLake during the years of the Hague survey(1883–89, 1890–91, 1893), the lake wasclearly resurveyed and triangulated byH.S. Chase and others, as published inmaps in the Hague report and reflected in

The Floor of Yellowstone Lake is Anything but Quiet!New Discoveries in Lake Mapping

by Lisa A. Morgan, Pat Shanks, Dave Lovalvo, Kenneth Pierce, Gregory Lee, Michael Webring, William Stephenson, Samuel Johnson,Carol Finn, Boris Schulze, and Stephen Harlan

Facing page: Plate 1. From top left: (A) Henry Elliott's 1871 map of Yellowstone Lake. The headwaters of the Snake River, Upper Valley ofthe Yellowstone River, and Pelican River are shown. The area now known as West Thumb is referred to as the South West Arm. (B) W.H.Jackson photo of the survey boat, The Anna, with James Stevenson (left) and Chester Dawes on July 28, 1871. (C) 1896 map of YellowstoneLake and surrounding geology as mapped in the Hague survey. (D) 1992 Kaplinski map. (E) New high-resolution bathymetric map acquiredby multibeam sonar imaging and seismic mapping. The area surrounding the lake is shown as a gray-shaded relief map.

“A man stands on the shore with a compass and takes a bearing to the man in theBoat as he drops the lead, giving a signal at the time. Then the man in the Boattakes a bearing to the fixed point on the shore where the first man is located andthus the soundings will be located on the chart...[Elliott will] make a systematicsketch of the shore with all its indentations [from?] the banks down, indeed, mak-ing a complete topographical as well as a pictorial sketch of the shores as seen fromthe water, for a circuit of at least 130 miles. He will also make soundings, at var-ious points.”


Plate 1. The 1896 map built upon theElliott map and refined areas on the shore-line, such as in the Delusion Lake areabetween Flat Mountain Arm and BreezePoint. Where the Elliott map of Yellow-stone Lake shows Delusion Lake as an armof the lake, the Hague map delineates itsboundaries and identifies swampy areasnearby. The maps from the Hague surveyalso include a rather sophisticated geolog-ic map of the subaerial portions of the parkaround the lake.

The next significant attempt to mapYellowstone Lake came a hundred yearslater and employed a single-channel echosounder and a mini-ranger for navigation,requiring interpolation between tracklines. Over 1475 km of sonar profiles werecollected in 1987, using track lines spacedapproximately 500 m apart and connectedby 1–2 km-spaced cross lines. An addi-tional 1150 km of sonar profiles were col-lected in 1988 to fill in data gaps from the

1987 survey. The map identified manythermal areas on the floor of the lake. Theresulting bathymetric map has served asthe most accurate lake map for Yellow-stone National Park for over a decade, andhas proven invaluable in addressing seri-ous resource management issues, specifi-cally monitoring and catching the aggres-sive and piscivorous lake trout.

Ten years after that bathymetric map,development of global positioning tech-nology and high-resolution, multi-beamsonar imaging justified a new, high-reso-lution mapping effort in the lake. Mappingand sampling conducted in 1999–2002 asa collaborative effort between the USGS,Eastern Oceanics, and the National ParkService utilized state-of-the-art bathymet-ric, seismic, and submersible remotely-operated vehicle (ROV) equipment to col-lect data along 200-m track lines with laterinfill, where necessary. The 1999–2002mapping of Yellowstone Lake took 62

Figure 1. (A) Index map showing the 0.64-Ma Yellowstone caldera, the distribution of itserupted ignimbrite (the Lava Creek Tuff, medium gray), post-caldera rhyolitic lava flows(light gray), subaerial hydrothermal areas (red), and the two resurgent domes (shown asovals with faults). The inferred margin of the 2.05-Ma Huckleberry Ridge caldera is alsoshown. (B) (facing page) Geologic shaded relief map of the area surrounding YellowstoneLake. Yellow markers in West Thumb basin and the northern basin are locations of active orinactive hydrothermal vents mapped by seismic reflection and multibeam sonar. (C) (facingpage) Color shaded-relief image of high-resolution, reduced-to-the-pole aeromagnetic map.Sources of the magnetic anomalies are shallow and include the post-caldera rhyolite lavaflows (some outlined in white) that have partly filled in the Yellowstone caldera. Rhyoliticlava flows (outlined in white) underlying Yellowstone Lake are shown clearly in this map.

ii

1A

N

0 10 20 30 40 50 KM

X

X

Yellowstone Lake

Yellowstone National Park

2.05-Ma Huckleberry Ridge caldera boundary

postcollapse rhyolite lava flows

hot spring areas

0.64-Ma Yellowstone caldera boundary

Lava Creek Tuff

Norris-MammothCorridor

resurgent domes

l l l l ll

Yellowstone Plateau

Acronyms used in figures

BFZ: Buffalo Fault ZoneEBFZ: Elephant Back Fault ZoneEF: Eagle Bay Fault ZoneHFZ: Hebgen Fault ZoneIP: Indian PondLHR: LeHardy RapidsLV: Lake VillageMB: Mary BayPV: Pelican ValleyQa: Quaternary alluvium (deltaic sedi-ments)Qg: Quaternary glacial depositsQh: Quaternary hydrothermal depositsQhe: Quaternary hydrothermal explo-sion depositsQl: Quaternary shallow lake sediments(shallow water deposits and submergedQld: Quaternary deep lake sediments(laminated deep-basin deposits)Qls: Quaternary land slide depositsQpca: Quaternary Aster Creek flowQpcd: Quaternary Dry Creek flowQpce: Quarternary Elephant Back flowQpch: Quaternary Hayden Valley flowQpcl: Quaternary tuff of Bluff PointQpcm: Quaternary Mary Lake flowQpcn: Quaternary Nez Perce flowQpcp: Quaternary Pitchstone PlateauflowQpcw: Quaternary West Thumb flowQpcz: Quaternary Pelican Creek flowQps: Quaternary tuff of Bluff Point Qs: Quaternary sedimentsQt: Quaternary talus and slope depositsQvl: Quaternary Lava Creek Tuff Qy: Quaternary Yellowstone GroupignimbritesSI: Stevenson IslandSP: Sand PointSPt: Storm PointTFZ: Teton Fault ZoneTl: Tertiary Langford Formation vol-canics TL: Turbid LakeTli: Tertiary Langford Formation intru-sivesTv: Tertiary volcanic rocksYR: Yellowstone River

Spring 2003 17

IP TLPV

Frank Is.

SoutheastArm

SouthArm

LV SPt

SP

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Tv

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northern basin

YELLOWSTONE CALDERAMARGIN

Qy

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centralbasin

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The Promontory

Flat Mtn. Arm

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Dot Is.

QpcnQpcn

AsterCreekflow

Elephant Back flow

Qmf

Qy

Qy

1B

Qpc?

WestThumb flow

Qpc?

1C

Spruce Creekflow

Tv(?)Tv

Tv

Tv

Qpcd

l l

l ll

ll

ll

ll

l

-47.1

-134.8

-257.3

-310.1

-413.6nT

105.4

-203.5

ll

ll

l

ll l l

0 10 kmll

44º20'

44º15'

44º25'

44º30'

44º35'

44º36'44º36'

44º15'

-110º10'-110º40'-110º10'-110º20'-110º40'-110º40'

Glossary of termsamphipods: crustaceans of small size and laterally-compressed bodyanastomozing: joining of the parts of branched systemsbathymetric: relating to the measurement of depth and floor contour of bodies of waterbreccia: sharp fragments of rock embedded in a fine-grained matrix (as sand or clay)brittle-ductile transition zone: area where brittle and malleable rock meet beneath the earth’s surfacedB: decibeldiatomaceous: consisting of or abounding in diatoms (unicellular or colonial algae having silicified cell walls)en echelon: referring to an overlapped or staggered arrangement of geologic features fathometer: tool used to measure fathoms (6-foot units used to measure water depth)graben: a depressed segment of the earth’s crust bounded on at least two sides by faults and generally longer than it iswideH2S: hydrogen sulfideka: thousand years agolacustrine: of, relating to, formed, or growing in lakeslaminated: composed of layers of firmly united materiallobate: having lobesMa: million years agomW/m2: milliWatt per square meterpotamodromous: migratory in fresh waterreduced-to-the-pole map: aeromagnetic map designed to account for the inclination of Earth’s magnetic field. Princi-pal effect is to shift magnetic anomalies to positions directly above their sources.seismic reflection profile: a continuous record of sound waves reflected by a density interfacesilicic: of, related to, or derived from silica or siliconstrike-slip displacement: displacement whose direction of movement is parallel to the direction of its associated faultU-series disequilibrium dating: a method of determining the age of a desposit by analyzing the isotopes produced byradioactive decay of uranium isotopes

Most definitions from Webster’s Third New International Dictionary (1981)


days over a 4-year period, compared toHayden’s survey of 24 days in 1871. Itbegan in 1999 with mapping the northernbasin and continued in 2000 in WestThumb basin, in 2001 in the central basin,and in 2002 in the southern lake includingthe Flat Mountain, South, and SoutheastArms (see Plate 1E). Unlike any of the pre-vious mapping efforts, the 1999-2002swath multi-beam survey produced con-tinuous overlapping coverage, collectingmore than 220,000,000 soundings and pro-ducing high-resolution bathymetricimages. Seismic reflection records of the

upper 25 m of the lake bottom wereobtained along with the bathymetry in theentire lake excluding the South and South-east Arms. This effort has produced a mapthat is accurate to the <1-m scale in mostareas. The following report focuses onresults of this mapping effort and the inter-pretation of the newly discovered features.

GEOLOGIC SETTING

Powerful geologic processes in Yel-

lowstone National Park have contributedto the unusual shape of Yellowstone Lake,which straddles the southeast margin ofthe Yellowstone caldera (Figure 1A), oneof the world’s largest active silicic volca-noes. Volcanic forces contributing to thelake’s form include the explosive, caldera-forming, 2.05-Ma eruption of the Huckle-berry Ridge Tuff, followed by eruption ofthe 0.64-Ma Lava Creek Tuff. Followingexplosive, pyroclastic-dominated activity,large-volume rhyolitic lava flows wereemplaced along the caldera margin, infill-ing much of the caldera (Figures 1A, B). A

smaller caldera-forming event about 140ka, comparable in size to Crater Lake, Ore-gon, created the West Thumb basin. Sev-eral significant glacial advances and reces-sions continued to shape the lake and over-lapped the volcanic events. Glacial scourdeepened the central basin of the lake andthe faulted South and Southeast Arms(Figure 1B). More recent dynamicprocesses shaping Yellowstone Lakeinclude currently active fault systems,

development of a series of postglacialshoreline terraces, and postglacial (<12-15 ka) hydrothermal-explosion events,which created the Mary Bay crater com-plex and other craters.

The objective of the present work is tounderstand the geologic processes thatshape the lake floor. Our three-prongedapproach to mapping the floor of Yellow-stone Lake located, imaged, and sampledbottom features such as sublacustrine hot-spring vents and fluids, hydrothermaldeposits, hydrothermal-explosion craters,rock outcrops, glacial features, slump

blocks, faults, fissures, and submergedshorelines.

RESULTS AND DISCOVERIES OF HIGH-RESOLUTION MAPPING

Topographic margin of the caldera.

Geologic maps show the topographicmargin of the Yellowstone caldera as run-ning below lake level in Yellowstone Lakebetween the western entrance to Flat

landslidedeposits

hydrothermalvents

ejectadeposits

explosioncraters

graben

spirefield

fissures

PelicanRoost

lavaflows

lava flows

StormPoint

Indian Pond

Qhe

Mary Bay

TurbidLake

SteamboatPoint

hydrothermal vents

submergedlakeshoreterraces

StevensonIsland

Elliot'sCrater

PelicanValley

A

A'

B

B'

GullPt.

BridgeBay

West Thumb Basin Northern Basin

Qs

44o30'

44o

31'

44o32'

44o33'

44o34'

44o35'

Qpce

Qpce

Qpce

Qs

Qs QylQci

Qhe

Qhe

Tl

Qyl

Tl

Qyl

QsTl

Qpcw

Qpcw

Qpcw

110 16o '110 18

o '110 20o

'

110 24o

'

110 26'o

YellowstoneRiver

Qpcw

Qyl

SandPt.

Qyl

LakeVillage



DuckLake

N

QsQs

Qs

Qs

Qps

Qps

Qh

Qhe

Qpce

Qpcd

Qpcd

Qpcw

QpceQpcw

110o34' 110o30'110o32'

44o24'

44o28'

44o26'

Qh

Qpcd

1 km

hydrothermalvents

hydrothermal vents

explosioncrater lava

flows

lavaflows

1 km

West Thumboutlet toYellowstoneLake

Figure 2. (A) New high-resolution bathymetric map of the West Thumb basin of Yellowstone Lake, acquired by multibeam sonar imagingand seismic mapping in 2000, showing a previously unknown ~500-m-wide hydrothermal explosion crater (east of Duck Lake), numeroushydrothermal vents, submerged lakeshore terraces, and inferred rhyolitic lava flows that underlie 7- to 10-m of post-glacial sediments. (B)High-resolution bathymetric map of the northern basin of Yellowstone Lake, acquired in 1999, showing large hydrothermal explosion cratersin Mary Bay and south-southeast of Storm Point, numerous smaller craters related to hydrothermal vents, and landslide deposits along theeastern margin of the lake near the caldera margin. Post-caldera rhyolitic lava flows underlie much of the northern basin. Fissures west ofStevenson Island and the graben north of it may be related to the young Eagle Bay fault (see Fig. 1B).

Spring 2003 19

Mountain Arm and north of Lake Butte(Figure 1B). Our mapping of the centralbasin of Yellowstone Lake in 2001 identi-fied the topographic margin of the Yel-lowstone caldera as a series of elongatedtroughs northeast from Frank Island acrossthe deep basin of the lake. Based on ournew data and high-resolution aeromagnet-ic data, we infer the topographic margin ofthe Yellowstone caldera to pass throughthe southern part of Frank Island.

Rhyolitic lava flows.

Large-volume, subaerial rhyolitic lavaflows on the Yellowstone Plateau controlmuch of the local topography and hydrol-ogy. Characteristic lava-flow morpholo-gies include near-vertical margins (someas high as 700 m), rubbly flow carapaces,

hummocky or ridged tops, and stronglyjointed interiors. Stream drainages tend tooccur along flow boundaries, rather thanwithin flow interiors.

A major discovery of the lake surveysis the presence of previously unrecognizedrhyolitic lava flows underlying much ofthe lake floor. Field examination of rhyo-lite flows shows that many areas identifiedthrough the aeromagnetic mapping as hav-ing low magnetic intensity values corre-spond to areas with hydrothermal activity,

or faulting or fracturing along whichhydrothermal alteration has occurred. Webelieve the lava flows are key to control-ling many morphologic and hydrothermalfeatures in the lake.

Areas of the lake bottom around theperimeter of West Thumb basin (Figures2A, 2B) have steep, nearly vertical mar-gins, bulbous edges, and irregular hum-mocky surfaces, similar to postcollapserhyolitic lava flows of the YellowstonePlateau. Seismic reflection profiles in thenear-shore areas of West Thumb basinshow high-amplitude reflectors (indicat-ing low magnetic intensity) beneath about7–10 m of layered lacustrine sediments(Figure 3A).

Areas such as the West Thumb andPotts geyser basins in West Thumb basin,and Mary Bay in the northern basin, cur-rently have extremely high heat flow val-ues (1650–15,600 mW/m2). Current heatflow values in Bridge Bay (580 mW/m2)are relatively low compared to Mary Bay,

Figure 2D. High-resolution bathymetricmap of the South, Southeast, and FlatMountain Arms, acquired by multibeamsonar imaging in 2002, showing the glaciat-ed landscape of the lake floor in the south-ernmost part of Yellowstone Lake and sever-al faults. The bathymetry in the SoutheastArm contains many glacial meltwater andstagnant ice block features; the area is infor-mally referred to as the "Potholes of theSoutheast Arm," and resembles much of thekettle dominated topography mapped byKen Pierce and others in Jackson Hole(inset image).

Figure 2C. High-resolution bathymetric mapof the central lake basin, acquired by multi-beam sonar imaging and seismic mapping in2001, showing the Yellowstone caldera topo-graphic margin, a large hydrothermal explo-sion crater south of Frank Island, and numer-ous faults, fissures, and hydrothermal vents asindicated.

central basin

Tv?

Tv

Qs

Tv

Tv

Tv?

ParkPoint

FrankIsland

DotIsland

lavaflows

calderamargin

explosioncrater

hydrothermalvents

hydrothermalvents

lavaflow

l l1 km

Qpca

Qpca

Eagle Bayfaultzone

Qpce

Qpca

Qy

Central Basin

Qpcw

-110o27'30" -110o20'

44o25'

44o30'

Delusion Lake

ElkPoint

Qs

Qs

Qs

Qs

Qs

South, Southeast, and Flat Mountain Arms

1 km

1 km

"Potholes of the Southeast Arm"


yet the Bridge Bay area has low magneticintensity values. Evidence for pasthydrothermal activity is present as inac-tive hydrothermal vents and structures, andmay have been responsible for demagnet-

ization of the rocks there. South of BridgeBay and west of Stevenson Island, lowmagnetic intensity values reflect activehydrothermal venting and relatively highheat flow values. Low magnetic intensityvalues in the northern West Thumb basinalso may be due to past hydrothermalactivity, as evidenced by vent structuresthere. Comparison of geologic maps (Fig-ure 1B) with the high-resolution aeromag-netic maps shows a crude relation of mag-netic anomalies to the mapped individuallava flows on land (Figure 1C).

The magnetic signatures, combinedwith the high-resolution bathymetric andseismic reflection data, allow identifica-tion and correlation of sediment-coveredrhyolitic lava flows far out into the lake(Figures 1, 2). For example, the AsterCreek flow (Qpca) southwest of the lake(Figure 1C) is associated with a consis-tent, moderately positive, magnetic anom-aly that extends over the lake in the south-

east quadrant of West Thumb basin, alongthe southern half of the West Thumb chan-nelway, and over the central basin of thelake well past Dot and Frank Islands (Fig-ures 1, 2). The Aster Creek flow has fewmapped faults, and few areas that havebeen hydrothermally-altered. Similarly,the West Thumb flow (Qpcw) can betraced into the lake in northeastern WestThumb basin, along the northern half ofWest Thumb channelway, and into thenorthern basin beneath Stevenson Islandand Bridge Bay (Figure 2C). In contrast,the Elephant Back flow contains a well-developed system of northeast-trendingfaults or fissures that has been extensivelyaltered so that the magnetic signature ofthis unit is fractured with a wide range ofvalues in magnetic intensity (Figure 2D).

Field examination of subaerial rhy-olitic lava flows indicates that negativemagnetic anomalies, for the most part, areassociated with extensive hydrothermal

1 km

3A

B.

3B

ll

l

0.00

36.25

72.50

dept

h (m

)

B'

A'

B

A

domalfeature

gaspocket

uplifted, tilted blockwith deformedsediments

vent

domed sediments

fault domed sediments

high-amplitude reflector

draped lacustrinesediments

lacustrinesediments

water bottom

lacustrinesediments gas

pockets

ventdomalstructures

vent

gas pockets

water bottom

1 km

0.00

36.25

72.50

108.75

145.00

dept

h (m

)

ll

ll

l

r (rhyolite flow)

Figure 3. (A) High-resolution seismicreflection image from northwestern WestThumb basin showing high-amplitude(red) reflector interpreted as a sub-bottomrhyolitic lava flow. Glacial and lacustrinesediments, marked in blue, overlie thisunit. (B) High-resolution seismic reflec-tion image across part of Elliott's explo-sion crater, showing small vents, gas pock-ets, and domed sediments in the lacustrinesediments that overlie the crater flank.Lacustrine sediment thickness in the maincrater indicates 5-7 thousand years of dep-osition since the main explosion. Morerecent explosions in the southern part ofthe large crater ejected post-crater lacus-trine sediments and created new, smallercraters and a possible hydrothermalsiliceous spire.

yellowstone science · mapping yellowstone lake predator and prey at fishing bridge. as director of...

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