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

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