tsunami geology – what do we know? what do we want to...
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TSUNAMI GEOLOGY –What do we know?
What do we want to know?
Jody BourgeoisEarth & Space Sciences
University of Washington
TSUNAMI GEOLOGY –What do we know?
What do we want to know?
Jody BourgeoisEarth & Space Sciences
University of Washington
Credit to Hig[Bretwood Higman}
Digital Globe
Jantang, Aceh 500 m
Higman, UW
Nicaragua 1992 tsunami effects, le PopoyoBourgeois, 1993, in Higman and Bourgeois, in press
Nicaragua 1992 tsunami effects, le PopoyoBourgeois, 1993, in Higman and Bourgeois, in press
Tsunami approaching the shore: The tsunami may approach the beach as a breaking wave. Sometimes the water will recede before this wave.
Higman graphic
Tsunami arrives on shore: The tsunami will surge inland. Because the tsunami wave is very long, the water remains high after the wave arrives.
Higman graphic
Tsunami does damage: The tsunami will flow violently inland, carrying whatever lies in its path.
Higman graphic
Tsunami pauses: The water may stop flowing before returning to the sea.
Higman graphic
Water withdraws: Floating debris are pulled back into the ocean.
Higman graphic
More tsunami waves are likely: Usually there will be multiple tsunami waves. Some of these later waves can be larger than the first wave.
T = 20 - 60 minutesHigman graphic
Possible [partial] analogues?
•Tidal bores•Dam breaks•Turbidity currents •Pyroclastic flows
Higman graphic
Fully developed boundary layerHigh turbulence at head
Quasi-steady uniform flow?
Higman
Spring 1987
Brian Atwater,USGS at UW
June 2005
Mary Ann Reinhart
Coast of Washington State
April 1987 – Willapa Bay, Washington State coast
Mary Ann Reinhart
BASIC QUESTIONS:
Is it a tsunami deposit?What was the source?How big was the tsunami?
[height, velocity]How many waves?Are there other, older deposits?What is frequency of deposits?
1957 tsunami from Aleutians
1
2
3
Oahu, Hawaii
NOAA slide set
Copalis deposit
Copalis River bank, Washington State coast
grassy field c. 300 years ago
tsunami deposit
Hypothesis:mudflat deposits in years after tsunami
One approach: study by analogueand case histories
1960 southern ChileMw 9.5
max runup 25 mHilo runup 10 m
Field work 1989
analogue?
1960 tsunami deposits
rock
The tsunami spread beach and river sediments over farmers’ fields.
In marsh
stove-pipecorer
1989 Chilean-American field crew, Rio Lingue marshJB 1989
Fine deposits
May 1960 farmer’s land
22 May 1960 tsunami deposit
post-1960 marsh mudRio LingueChile
splitstove-pipecore1989
TSUNAMI-DEPOSIT “TRINITY”
Copalis deposit
Copalis River bank, Washington State coast
grassy field c. 300 years ago
tsunami deposit
“Confirmation” by analogue:mudflat deposits in years after tsunami
April 1987
Mary Ann Reinhart
BASIC QUESTIONS:
Is it a tsunami deposit?What was the source?How big was the tsunami?
height, velocityHow many waves?Are there other, older deposits?What is frequency of deposits?
Reinhart (unpubl. M.S.)
Map of tsunami depositsin SW Washington
Sediment transport model (1989-1990)
AtwaterMusumi-Rokkaku
SatakeTsujiUeda
Yamaguchi2005
USGS & UW Press
Paleotsunami Deposits
Other DepositsTsunami Deposits
Tsunami Flows
Differentiation
Common Process
Source
Constraints
Propagation
Taphonomy
SedimentModeling Model
Validation
JUNE 2005 NSF Tsunami Deposit Workshop
“Matrix of knowledge”
Earthquake
AsteroidVolcano
Landslide
Higman graphic
Research question: Can we use tsunami geology to help distinguish tsunami sources?
Cretaceous-Tertiary boundary in Texas
65 million years agoglobal mass extinction
Unusual, coarse-grained layer
in North AmericanGulf Coast region
Brazos River area, Texas
Darting Minnow Creek
Cottonmouth Creek JB/87
Shear stress necessary to transport largest clastsrequired wave 50-100 m high in 100 m water depth
Bourgeois, Hansen, Wiberg & Kauffman 1988
Outstanding problem:
The Chicxulub impactwas in shallow water.
How can we model such a tsunami?
How do we evaluate “outrageous” claims for tsunami depositsand tsunami geomorphology?
“chevrons”better known as parabolic dunes
White Sands, New Mexico
Idaho, Snake River plain
eastern Washington State
These are well studied and understood eolian bed forms
How are large boulders transported by storms and by tsunamis?
Can we tell which is which?
Scheffers, 2005 NSF Workshop
What is the offshore record of tsunamis?
Paleotsunami Deposits
Other DepositsTsunami Deposits
Tsunami Flows
Differentiation
Common Process
Source
Constraints
Propagation
Taphonomy
SedimentModeling Model
Validation
JUNE 2005 NSF Workshopon Tsunami Deposits[or Tsunami Geology]
Storm with storm surge
Short waves dissipaterapidly carrying sedimentshort distatnces
Flow reversesoften
Steep front withenhanced turbulence
Erosion steepens beach
Erosionfocused at top ofbeachSteep fronted tsunami
Ordinary conditions
Research priority: Distinguish storm deposits
from tsunami deposits
Higman
Storm with storm surge
Short waves dissipaterapidly carrying sedimentshort distatnces
Flow reversesoften
Steep front withenhanced turbulence
Erosion steepens beach
Erosionfocused at top ofbeachSteep fronted tsunami
Ordinary conditions
Research priority: Distinguish storm deposits
from tsunami deposits
Bedload, prolonged reworking
Suspended load, rapid deposition
Higman
Katrina effects, Deer Island, off Biloxi, Mississippi [Eipert, in progress]
Higman, 2005
Higman graphic
Higman, in progress
Research priority: To quantify the relationship between tsunami behaviorand the geologic recordof deposition and erosion
Example of a site survey, Sri Lanka2005
Data collected includes:
•Topographic profile•Tsunami elevations,
inundation, runup•Tsunami flow depth•Tsunami deposit
documentation &samples
DamageEyewitness accounts
former soil surface
tsunami sand deposit
TsunamiFlow Speed
Inverse Modeling of Tsunami Flow Speed from Tsunami Deposits – Jaffe et al.
Rousecalculation
Tsunami deposit Sediment concentration in water column necessary to produce deposit
U* [Uf]
Atwater and Moore, 1992
Andy Moore, UW Ph.D.
Characteristic <u> = 4 m/sCharacteristic depth = 1.4 m
Moore, M.S. thesis & 2001 workshopMoore and Mohrig (1995 abstr.)
Calculations from Moore’s M.S. analysis were used to calibrate Koshimura and Mofjeld’s tsunami model
Koshimura & Mofjeld
models
(Willapa Bay sedimentationand erosion model)
Lesser & Gelfenbaum
Study of presence, absence, distribution, and character of tsunami deposits can
1) Help ground-truth models2) Provide calibration for
models3) Provide data where models
are difficult to run.
Blue -- erosionRed -- deposition
Research priorities:•Develop and comparetsunami sedimentation models
[discussions later today]•Conduct laboratory experiments•Continue field studies --
develop protocols for field and lab [e.g., grain size] analyses
•Continue careful description of sedimentary structures and textures
Kelsey et al., 2004Kelsey et al. 2004
Importance of longer-term records
Tsunami deposits tell us about larger, prehistoric tsunamis, even in regions with large historic tsunamis.
HOKKAIDO
Nanayama, Atwater, Satake and others
Applications of tsunami geology studies
PaleoseismologyNeotectonics – plate tectonicsArchaeologyCoastal geomorphologySeismic & tsunami hazardsEducation & outreach
Tsunamis in understandingtectonic behavior
FUNDINGU.S. National Science Foundation
Russian Foundation for Basic Research
LARGE Polar with plate boundaries
OKH
BER
Can we quantify the rate of convergence?
in Bourgeois et al. (2006)courtesy of
Kevin Mackey &Kaz Fujita
recentearthquakes
11 Nov 1969
KAMCHATKA LANDMw 7.7 tsunamigenic earthquake
Stolbovaya field site
peat & volcanic ash
Bering Sea coast
Stolbovaya siteProfile 1, trench 104
1969 Ozernoi tsunami deposit ->1964 Shiveluch volcanic ash ->
paleo-tsunami deposit ->
paleo-tsunami deposit ->
Shiveluch c. 1650 A.D. ->
Ksudach caldera c. 250 A.D. ->
The 1969 tsunami runup at this profile was about 5 meters.
Maximum elevation of 1969? tsunami deposits
Compared to a tsunami model ofpropagation
Southern deposits cannot be explained by 1969
Martin, Weiss, et al.,in progress
max deposit elevation (m)
Going back in time, we have 14 profiles~50 excavations with records >3000 years.
Bourgeois et al. 2006
Tsunami frequencyper 1000 years
Surface erosion
Bioturbation, weathering, infiltration of fines
Liquefaction
Loss ofrecords byerosion
Higman graphic
[aside] Research priority: Understand “taphonomy”
of tsunami deposits[taphonomy = post-life history]
Tsunami deposits support a version of thistsunami model, which inverts to fault deformation with
~3 m horizontal shortening
1969 Ozernoi earthquake modeled by tsunami data & deposits indicates c. 3 m horizontal shortening
Recurrence intervals for such tsunamis (from deposits) indicates shortening
of ~15 mm/yr over last 4000 yr
Long-Term Record Challenges
GeochronologyCorrelationStatistics
How many observationsare sufficient?
What is the preservation factor?
Going beyondtsunami recurrence
to earthquake recurrence
Going beyondtsunami recurrence
to earthquake recurrence
and onward to paleotsunami and earthquake magnitudes
Challenges
PaleogeographyPaleobathymetryPaleotopography
and onward to paleotsunami and earthquake magnitudes
Paleotsunami Deposits
Other DepositsTsunami Deposits
Tsunami Flows
Differentiation
Common Process
Source
Constraints
Propagation
Taphonomy
SedimentModeling Model
Validation
JUNE 2005 NSF Workshopon Tsunami Deposits[or Tsunami Geology]
Tsunami geology—a lot of digging
WE CAN USE (HISTORIC AND PRE-HISTORIC) TSUNAMI DEPOSITS AND TSUNAMI GEOMORPHOLOGY:
and where prehistoric tsunamis are larger; To help produce probabilistic hazard maps; To calculate tsunami recurrene intervals (typically centuries long); To understand tsunami behavior; To calibrate, test and enhance tsunami runup modeling; and To educate the public.
To reconstruct tsunamis in Earth history; To document tsunamis and tsunami hazard where unknown historically