activity 1 where are the volcanoes?...the world map. use the string of volcanoes within the aleutian...

888EarthComm

Volcanoes

GoalsIn this activity you will:

• Find the latitude andlongitude of volcanoesnearest your community whengiven a map of historicallyactive volcanoes.

• Search for and describepatterns in the globaldistribution of volcanoes.

• Make inferences aboutpossible locations of futurevolcanic activity.

• Understand that mostvolcanism occurs beneath the ocean.

• Understand that mapprojections distort regionsnear the poles and eliminatesome data.

Think about It

Volcanoes are one of nature’s most feared, yet spectacularactivities.

• Can volcanoes form anywhere on Earth? Why or why not?

What do you think? Record your ideas about this question inyour EarthComm notebook. Be prepared to discuss yourresponses with your small group and the class.

Activity 1 Where are the Volcanoes?

CS_Ch14_Volcanoes 3/2/05 3:02 PM Page 888

889Coordinated Science for the 21st Century


Investigate

1. “Thought experiments” areexperiments that scientists dream upand then run in their imagination,rather than in a real laboratory. Theyare a useful way to develop newideas and insights into scientificproblems. Here’s a thoughtexperiment for you to do, to helpyou understand the Mercator mapprojection. It wouldn’t even be toodifficult to do this in real life, if youcould obtain the right materials.

Visualize a large, see-through plasticball. Poke holes on opposite sides, andstick a wooden dowel or a chopstickthrough to make the North Pole andthe South Pole. Install a bright lightdirectly at the center of the ball,somehow. With a felt-tipped pen, drawa fake continent on the ball. Make thecontinent extend from near theEquator to near the North Pole. Now wrap a clear sheet of stiff plasticaround the globe, to make a tight-fitting cylinder that’s parallel to theEarth’s axis. See the figure on the rightfor how to arrange this. Turn the lighton, and observe how the border ofyour continent projects onto the plasticcylinder. Trace that image on thecylinder with the felt-tipped pen.Unwrap the cylinder from the globe,and lay it flat on the table. You nowhave a map with what’s called aMercator projection of your continent!

a) Describe how the image of yourcontinent is changed in shape(distorted) when it is projectedonto the cylinder.

b) If you drew a short east–west linewith a certain length near thesouthern end of your continent,and another east–west line withthe same length near the northernend of your continent, how wouldthe lengths of the lines comparewhen they are projected onto thecylinder map?

c) If you drew a short north–southline with a certain length near thesouthern end of your continent,and another north–south line withthe same length near the northernend of your continent, how wouldthe lengths of the lines comparewhen they are projected onto thecylinder map?

d) How would the image of acontinent that is centered on theNorth Pole project onto thecylinder map?

e) Which part of your map showsthe least distortion?

transparentplastic sleeve

woodendowel

transparentplastic ball

light


890EarthComm

Volcanoes

2. Obtain the USGS map called ThisDynamic Planet. Look at the mapkey, also shown above, to learn themeaning of the various symbolsand how to use the map scale.

a) What do each of the four kindsof triangles represent?

b) What do the solid red linesrepresent?

c) Describe how the scale of themap changes with latitude.

d) Does the map cover the entireEarth? Why or why not?

3. For each time interval of volcanicactivity shown on the map, find thelatitude and longitude of threevolcanoes closest to your community.

a) Make a data table to recordyour results. When complete,the data table should list 12 volcanoes.

b) Compare your data with that ofother groups in your class. Didyour class agree on the locationsof the nearest historically activevolcanoes? How did you resolveany differences?

4. Obtain a copy of a world map.Use this map to summarize anypatterns in the global distributionof volcanoes.

a) When volcanoes follow a linearpattern, draw a thick line onthe world map. Use the stringof volcanoes within theAleutian Islands and southernAlaska as an example.

b) For the red lines that appear onthe USGS map, draw thin lineson your copy of the map. Seethe examples in the PacificOcean near Oregon andWashington.

c) Where volcanoes are lessconcentrated, outline (circle) thearea that they cover. Try to beas accurate as possible. See thegroup of volcanoes in theCascades as an example.

5. When your map is complete,answer the following questions inyour notebook:

a) Are most volcanoes found inrandom places or do they showa trend or pattern? Explain.

Erupted A.D. 1900 through 1993

VOLCANOES_(from the Global Volcanism Program, Smithsonian Institution, Washington, D.C.)

Erupted A.D. 0 to A.D. 1900

Holocene eruptions (within past 10,000 years), B.C. andundated A.D. eruptionsUncertain Holocene activity and fumarolic activity

400200

200 400 800 1000600 1200 KILOMETERS0

600 800

70˚

50˚

30˚10˚EQUATOR

Scale 1:30 000 000 at the EquatorOne centimeter equals approximately 300 kilometers (186 miles) at the Equator

One inch equals approximately 473 miles (762 kilometers) at the Equator

1000




b) Does the USGS map showvolcanoes that have not eruptedduring the last 10,000 years?

c) Does the USGS map showeruptions after 1993, or newvolcanoes?

d) Does the USGS map show anyvolcanoes associated with thered lines in the ocean basins?

e) What information does the mapgive about the size or hazard ofthe volcanoes?

f) Suppose that tomorrow avolcano forms somewhere inthe United States. Could it form

in or near your state? Supportyour answer with evidence fromthis activity.

g) What are some limitations ofthe evidence you used?

By looking at a world map of recentvolcanic activity you found patternsin the data. This helped you to makeinferences about the possible locationof the next volcanic eruption in theUnited States. The data you looked

at are incomplete. This may limit the conclusions you can draw.However, you now have someknowledge that will help you decidewhere in the U.S. you might “stage”a volcanic eruption.

Reflecting on the Activity and the Challenge

Digging Deeper

THE GLOBAL DISTRIBUTION OF VOLCANOES

Volcanoes beneath the Sea

The USGS map This Dynamic Planet shows historical volcanic activitythroughout the world. It tells a story about how our dynamic planet releasesits internal storehouse of energy. No single source of data tells the wholestory, but a map is a great place to begin.

On average, about 60 of Earth’s 550 historically active volcanoes erupt eachyear. Geologists have long known that volcanoes are abundant along theedges of certain continents.The presence of volcanic rocks on the floors ofall ocean basins indicates that volcanoes are far more abundant under waterthan on land.


892EarthComm

Volcanoes

All of the Earth’s ocean basins have a continuous mountain range, called a mid-ocean ridge extending through them.These ridges, over 80,000 km longin total, are broad rises in the ocean floor.They are usually in water depths of1000 to 2000 m. Figure 1 shows a vertical cross section through a mid-oceanridge.At the crest of the ridge there is a steep-sided rift valley. Magma(molten rock) from deep in the Earth rises up into the rift valley to formsubmarine volcanoes.These volcanoes have even been observed by scientistsin deep-diving submersibles.All of the floors of the oceans, beneath a thin layerof sediments, consist of volcanic rock, so we know that volcanoes form allalong the mid-ocean ridges, at different times at different places.At a fewplaces along the mid-ocean ridges, as in Iceland, volcanic activity is especiallystrong, and volcanoes build up high enough to form islands.

Volcanoes on Land

Volcanoes that erupt on land are much more dangerous than volcanoesbeneath the ocean. Eruptions along the western edge of the United Stateshave formed the Cascades volcanic mountain range.They also form islandchains, like the Aleutians in Alaska.Volcanoes like these are common in anarrow belt all around the Pacific Ocean. Geologists call this the “Ring ofFire.” A famous example of an eruption along the Ring of Fire was thedramatic eruption of Mt. St. Helens in Washington in 1980.

Geo Wordsmid-ocean ridge: acontinuous mountain rangeextending through the Northand South Atlantic Oceans,the Indian Ocean, and theSouth Pacific Ocean.

rift valley: the deep centralcleft in the crest of the mid-oceanic ridge.

magma: naturally occurringmolten rock material.generated within the Earth

sea surfaceridgecrest

rift valley

lithos

phere

asthe

nosp

here

crust

irregular sea floor

risingmagma

10 km

flowingrock flowing

rock

plate # 2

plate # 1motion

motion

Figure 1 Cross section through a mid-ocean ridge.




Ring of Fire

Around the edges of the Pacific Ocean, the plates of the Pacific Ocean slidedown beneath the continents. Look at Figure 2 to see an example.The NazcaPlate, moving eastward from the East Pacific Ridge, slides down beneath thewest coast of South America.The plate is heated as it sinks into the muchhotter rocks of the deep Earth.The heat causes fluids, especially water, toleave the plate and rise into overlying hot rocks.The added water lowers themelting point of the solid rock. If enough water is added the rock melts andmagma is formed.The magma rises upward, because it is less dense than therocks. It feeds volcanoes on the overlying plate. Nearly four-fifths ofvolcanoes on land form where one plate slides beneath another plate.

Volcanoes Formed by Rifting on the Continents

Volcanoes in the East African rift valley form where two parts of the Africancontinent are moving apart from each other.The process is very similar towhat happens at mid-ocean ridges.The continental plate is stretched andbroken. One of the breaks becomes the main one, and opens up to form therift valley, as shown in Figure 3.

active volcanoes, plate tectonics, and the "ring of fire"

EurasianPlate

EurasianPlate

Indo-Australian Plate

Pacific Plate

Antarctic Plate Antarctic Plate

Cocos Plate

Scotia Plate

Caribbean Plate

North American Plate

Juan de Fuca Plate

"Ring of Fire"

NazcaPlate

SouthAmerican

Plate

ArabianPlate

AfricanPlate

divergent plate boundaries

diffuse poorly defined boundariestransform boundaries

convergent plate boundaries volcanoes

Figure 2 The plates of the Earth, and the “Ring of Fire” around the Pacific.The circles show active volcanoes.


894EarthComm

Volcanoes

In the United States,continental rifting longago formed the rocksthat make up the tall cliffson the western bank ofthe Hudson River.Theserocks formed whenmagma intruded the crustduring this rifting.Therocks are seen for morethan 80 km along thebank of the Hudson Riverand can be up to 300 mthick! Other evidence ofmagma formed duringthis rifting is found inmany states along theEast Coast.

Volcanoes at Hot Spots

Volcanoes discussed so far occur near the edges of plates. However, a smallpercentage of volcanoes occur in the interior of a plate.The HawaiianIslands, shown in Figure 5, are an example. Studies of volcanic rock show that

Geo Wordslava: molten rock that issuesfrom a volcano or fissure.

hot spot: a fixed source ofabundant rising magma thatforms a volcanic center thathas persisted for tens ofmillions of years.

map projections: the processof systematically transformingpositions on the Earth’sspherical surface to a flat mapwhile maintaining spatialrelationships.

Mercator projection: a mapprojection in which the Equatoris represented by a straight linetrue to scale, the meridians by parallel straight linesperpendicular to the Equatorand equally spaced accordingto their distance apart at theEquator, and the parallels bystraight lines perpendicular tothe meridians and the samelength as the Equator. There isa great distortion of distances,areas, and shapes at the polar regions.

Figure 4 Mount Kilimanjaro is a famous example of volcanism at a continental rift. Many othervolcanoes in the East African rift valley have erupted in historic times.

B.B.

A.A.

upwarpingupwarping

rift valleyrift valley

asthenosphereasthenosphere

lithospherelithosphere

Figure 3 Formation of a rift valley on a continent.




the islands getolder to thenorthwest. Onlythe youngest island,the “big island” ofHawaii, has activevolcanoes.

Here’s howgeologists explainthe pattern of theHawaiian Islands.Deep beneathHawaii, there is afixed source ofabundant risingmagma, called ahot spot.As thePacific Plate moves to the northwest, away from the East Pacific Ridge, itpasses over the fixed hot spot. Magma from the hot spot punches its waythrough the moving plate to form a chain of islands.The sharp bend in thechain was formed when the direction of movement of the plate changedabruptly at a certain time in the past. Far to the northwest the chain consistsof seamounts.

Map Projections

There is always a big problem in drawing a map of the world, because youhave to try to show the curved surface of the Earth’s globe on a flat sheet ofpaper. Many different ways of doing this, called map projections, have beendeveloped, but they all have some kind of distortion.The USGS map uses aMercator projection.As you move away from the Equator, the mapbecomes more and more distorted. For example, it makes all lines of latitudelook like they are equal in length.This makes it difficult to measure distanceson the map.Another problem is that the USGS map stops at 70° north andsouth latitude, because of the Mercator projection.This keeps you fromseeing all of the data. For example, the USGS map cuts off the mid-oceanridge north of Iceland.The scale of the map also presents a problem.Thelarger the area covered by the map, the less detail the map can show. In thiscase, the triangular symbols that represent volcanoes often overlap in areaswith many volcanoes.This makes them difficult to count.

120˚140˚160˚

50˚

PA C I F I C O C E A N

Aleutian Islands

Hawaiian Islands

Hawaiian Islands

Hawaiian Islands

Emperor

Seam

ounts

NorthAmerica

60˚

40˚

30˚

20˚

10˚

180˚160˚


Aleutian Islands

Emperor

Seam

ounts


Aleutian Islands

Emperor

Seam

ounts

Figure 5 The Hawaiian island chain and the Emperor seamount chain.

Geo Wordsseamount: a peaked or flat-topped underwater mountainrising from the ocean floor.

1. What evidence dogeologists have thatvolcanoes occur on theocean floor?

2. What is the Ring ofFire, and where is itlocated?

3. Where do mostvolcanoes on landform?

4. How are rift valleysformed?

5. What are hot spots?Provide an example ofa hot spot on Earth.

6. Why does thehorizontal scale of aMercator projectionincrease with latitude?

Check YourUnderstanding

CS_Ch14_Volcanoes 3/1/2005 5:56 PM 95

896EarthComm

Volcanoes

Understanding and Applying What You Have Learned

1. What difficulties did you havefinding the latitude and longitudeof volcanoes?

2. Where on Earth do most volcanoesoccur? Explain your answer.

3. Are most volcanoes on land causedby the Earth’s plates moving awayfrom each other or moving towardeach other? Explain your answer.

4. In your own words, describe thelikely cause of historically activevolcanoes in:

a) The continental United Statesb) The Aleutian Islands and

southern Alaskac) The Hawaiian Islands.

5. Based on your results from thisinvestigation, list the five statesthat you think are most likely toexperience the next volcaniceruption. Explain each choice.

6. Of the average of 60 volcanoesthat erupt in any given year, howmany are likely to erupt along theRing of Fire?

7. Why did the Mercator projectionnot show volcanoes near theEarth’s poles?

8. Do most volcanoes on land occurin the Northern Hemisphere or theSouthern Hemisphere? Explainwhy you think this is so.

Preparing for the Chapter Challenge

Think about how you can help theaudience understand why you chosethe probable location of the volcaniceruption for your story. Explain themap that you made for this activity.Note the volcanic eruptions that areclosest to your area. Explain wheremost volcanoes occur in the UnitedStates. You should also note wherethey have not happened recently.




Inquiring Further

1. Eruptions near your community

Find out more about the historicaleruptions at the volcanoes nearestyour community. The VolcanoWorld web site lists hundreds ofhistorically active volcanoes.(Consult the AGI EarthComm website for current addresses.) Yourdata table of latitudes and longitudes will help you toidentify them.

2. Volcanoes and the water on Earth(the hydrosphere)

Research to find answers to thefollowing questions, and any otherquestions which you have formed:

• How do volcanoes at mid-oceanridges affect the temperature of seawater?

• How do volcanoes change thechemistry of seawater?

• How does seawater affect thecomposition of the volcanic rock that is formed at the mid-ocean ridge?

• Would volcanoes affect a smallbody of seawater, such as theRed Sea, the same way as a largeocean like the Atlantic?

• Can a change in the volume ofvolcanic rock formed at mid-ocean ridges change sea level?


activity 1 where are the volcanoes?...the world map. use the string of volcanoes within the aleutian...

Documents