THE DEPOSITS OF TSUNAMIS WESLEY PESANTEZ, CATHERINE NIELD, COLIN WINTER

THE DEPOSITS OF TSUNAMIS WESLEY PESANTEZ, CATHERINE NIELD, COLIN WINTER

AN OVERVIEW OF OUR SEMINAR WHAT IS A TSUNAMI WHY STUDY TSUNAMIS PROPERTIES OF TSUNAMIS TSUNAMI HYDRODYNAMICS IDEALIZED DEPOSITS SEDIMENT TEXTURES DEPOSITIONAL, GEOMETRY, AND EROSION FEATURES CASE STUDIES

WHAT ARE TSUNAMIS TSUNAMIS, AS WE ALL KNOW, ARE CREATED MAINLY BY DEEP WATER EARTHQUAKES, SUBMARINE LANDSLIDES, VOLCANIC ERUPTIONS, OR (RARELY) ASTEROID IMPACTS TSUNAMIS CREATE LONG PERIOD WAVES THAT REACH INCREASED HEIGHTS WHICH CAN ONLY REACH A FEW METERS HIGH ABOVE SEA LEVEL BUT CAN SPAN TO HUNDREDS KILOMETERS IN LENGTH TSUNAMIS MOVE IN PULSES, A HUGE ONE THEN SMALL ONES IN SUCCESSION TO ONE ANOTHER, MOVING AT HIGH VELOCITIES TSUNAMIS ARE DISASTROUS EVENTS THAT, ALTHOUGH VERY BRIEF, CAUSE MUCH HARM TO PEOPLE AND NATURE WHICH SUPPORTS WHY THEY SHOULD BE STUDIED.

REASONS WHY WE STUDY TSUNAMIS TSUNAMIS, SURPRISINGLY, HAVE NOT BEEN STUDIED AS MUCH AS OTHER GEOLOGIC HAZARDS THE MAIN FOCUS OF STUDYING TSUNAMIS IS TO ESTIMATE THE INTENSITY AND FREQUENCY OF FUTURE TSUNAMIS BY LOOKING AT THE STRATIGRAPHIC RECORD. THIS ALLOWS US TO: PREDICT FUTURE HAZARDS PREPARE FOR FUTURE TSUNAMIS CURRENT RESEARCH SHOWS TSUNAMIS OCCUR ON AN INTERVAL OF APPROXIMATELY EVERY 10 YEARS IT IS ESSENTIAL TO DISTINGUISH TSUNAMIS AND COASTAL STORMS - THIS CAN BE DIFFICULT AT TIMES WHEN STUDYING MINOR TSUNAMI EVENTS

PROPERTIES OF TSUNAMIS FLOW VELOCITY DECREASES AND WAVE HEIGHT INCREASES AS IT ENTERS SHALLOW WATER EXTEND HUNDREDS OF METERS INLAND FROM THE BEACH MANY DIFFERENCES AND SIMILARITIES BETWEEN TSUNAMIS AND STORM DEPOSITS DEPOSITS RESULT FROM A FEW HIGH VELOCITY, LONG PERIOD WAVES THAT PICK UP SEDIMENT FROM THE BEACH AND EROSION ZONE FLOW DEPTH >10M DISTRIBUTE LOAD OVER A BROAD REGION

TSUNAMI HYDRODYNAMICS CONTINUOUS SURGE GRADUAL OFFSHORE RISING IN WATER FOLLOWED BY ONSHORE SURGE THAT FLOODS INLAND UNTIL THE WATER VOLUME DISTRIBUTED ACROSS THE LAND IS EQUAL AFTER FIRST PULSE THERE IS A RELAXATION PERIOD FOLLOWED BY PULSES OF FROM LOW SHORT PERIOD OCEAN WAVES SUPERIMPOSED ON THE PREVIOUS FLOOD

TSUNAMI HYDRODYNAMICS ELEVATED BORE WAVE ADVANCES AS A HIGHLY TURBULENT ELEVATED WALL OF WATER THAT CONSTANTLY BREAKS AS IT EXCEEDS THE SURF ZONE SMALLER WAVES FOLLOW WHICH CAUSES AN INCREASE IN FLOW DEPTH AND TEMPORARILY ACCELERATE FLOW VELOCITIES

TSUNAMI HYDRODYNAMICS RECESSION OF THE SEA RECESSION OF OCEAN COMMONLY PRECEDES THE HIGHEST/MOST DESTRUCTIVE TSUNAMI WAVE THIS MAY BE THE FIRST OR A SUBSEQUENT WAVE CAN RECEDE UP TO SEVERAL HUNDRED METERS FOR AS LONG AS 30 MINUTES BEFORE A STEEP BORE RUSHES ONSHORE AND INFILTRATES THE LAND

IDEALIZED DEPOSITS MOST TSUNAMI SAND DEPOSITS ARE <25CM THICK, AND TYPICALLY HAVE A BROAD, THIN GEOMETRY BECAUSE INUNDATION DURATION IS SHORT, SEDIMENT IS DISPERSED ALONG A RELATIVELY DEEP FLOW, AND VOLUME OF SEDIMENT IS LIMITED BY THE BRIEF ONSHORE FLOW

IDEALIZED DEPOSITS COBBLE- TO BOULDER- SIZED SLABS OF ROCK, BLOCKS OF CORAL, AND ORGANIC-RICH MUD ARE COMMONLY EXHUMED AND THEN DEPOSITED ON BACK BEACHES AND OVERWASH FLATS RIP UP CLASTS ARE COMMON IN LOWER, FINE-GRAINED SECTIONS OF TSUNAMI DEPOSITS MUD LAMINATIONS ARE COMMONLY FOUND EITHER WITHIN OR AT THE TOP OF THE EVENT BED DEPOSITS MATCH THE TOPOGRAPHY OF THE AREA - MAXIMUM HEIGHT OF DEPOSIT IS AROUND 50 METERS FROM THE BEACH

SEDIMENT TEXTURES, GRADING, AND STRATIFICATION TYPICAL SEDIMENT FEATURES OF TSUNAMI DEPOSITS INCLUDE: WELL TO POORLY SORTED SEDIMENTS HEAVY MINERAL LAMINA WITH AND AT THE BASE OF DEPOSITS ABRUPT BASAL CONTACTS TYPICALLY CONTAIN ONLY A FEW LAMINASETS NORMALLY GRADED

DEPOSITIONAL FEATURES TRUNCATED FLAME STRUCTURES, STATES THAT ONE OF THE FEATURES THAT ARE FOUND WHEN LOOKING FOR DEPOSITED TSUNAMI SEDIMENT, FLAMES ARE THE MOST PROMINENT FEATURES FOUND, HOWEVER THESE ARE ALSO CUT OFF WHILE BEING DEPOSITED, WHICH IS WHY THEY ARE RARE THESE FLAME STRUCTURES ARE MOST LIKELY CREATED BY THE LESS DENSE MUD/SILT LAYER THAT SHOOTS UPWARDS AND IS FOUND IN THE SANDY LAYER ABOVE.

GEOMETRY OF TRUNCATED FLAMES A) THE FIRST WAVE HITS AND DEPOSITS A THIN LAYER OF MUD AND SILT, LAID LATERALLY ON THE SURFACE B) THE SECOND WAVE, ALONG WITH THE RUNUP CURRENT, CAUSES A SHEAR SURFACE WITH THE BOTTOM LAYER, CAUSING THESE FLAMES TO BE PRODUCED C) COARSE GRAINED SEDIMENT IS THEN BROUGHT IN AND BEGINS TO FILL THE OPEN PITS WHILE AT THE SAME REMOVING THE TOP PARTS OF THE FLAME, EVENTUALLY IT LEADS TO A COARSE GRAINED LAYER D) FINALLY, A STAGNANT WAVE COMES IN AND PRODUCES A MUD LAYER ON TOP

DEPOSITIONAL FEATURES (CONTINUED) THE GRAINS THAT ARE DEPOSITED BY THE TSUNAMI FLOW A PATTERN OF (FROM BOTTOM TO TOP) : COARSE FINE COARSE EACH OF THESE GRAINS ARE CLEAR SEPARATED BY LAYERS WHILE ALSO SHOWING OTHER FEATURES EACH OF THESE SHOW A DIFFERENT WAVE COMING IN AND LEAVING

GENERAL WAYS A TSUNAMI CAUSES EROSION TSUNAMI BORES THESE ARE VERTICAL WALLS OF WATER MOVING AT HIGH VELOCITY THAT BEGIN TO ENTRAIN SEDIMENT AND BREAKS ONTO THE SHORE, EVENTUALLY FLOODING INLAND. RUNUP CURRENTS THESE ARE WAVES THAT DON T HAVE SUCH A HIGH VELOCITY BUT ARE TALL ENOUGH TO REACH ABOVE THE SEA LEVEL AND MOVE PAST THE SHORE, ENTRAINING SEDIMENT AND DEPOSITING DIFFERENT TYPE ACROSS THE SURFACE SEA LEVEL DROP DURING RECESSION OF THE SEA, SEDIMENT BECOMES EXPOSED TO THE ONCOMING WAVES THAT ENTRAIN THIS SEDIMENT AND DEPOSITS IT INLAND WHEN IN FLOODS

AN EXAMPLE OF EROSION ENVIRONMENT FROM THE IMAGE ON THE RIGHT WE SEE HOW THE TSUNAMI IS ABLE TO ENTRAIN SEDIMENT ON THE BEACH SURFACE AND LATER IS DEPOSITED ON THE MAINLAND ONCE REACHING A CERTAIN POINT, TSUNAMI WAVE CAN T DEPOSIT SEDIMENT ANYMORE SO IT THINS OUT AT THIS POINT

DISTINGUISHING BETWEEN TSUNAMI AND COASTAL STORM DEPOSITS DEPOSITIONAL CHARACTERISTICS THAT ARE USEFUL IN DISTINGUISHING THESE DEPOSITS INCLUDE: COMPOSITION AND THICKNESS SEDIMENT-TRANSPORT DISTANCE FROM THE SHORE LATERAL CONTINUITY GRAIN-SIZE DISTRIBUTION SEDIMENTARY STRUCTURES VERTICAL TRENDS WITHIN THE DEPOSIT TSUNAMI RIP UP CLASTS TSUNAMI MUD LAYERS

CASE STUDY 1: 2004 INDIAN OCEAN TSUNAMI TRIGGERED BY THE SUMATRA-ANDAMAN EARTHQUAKE, WITH THE EPICENTER LOCATED OFF THE WEST COAST OF NORTHERN SUMATRA SPREAD ACROSS THE INDIAN OCEAN, AND STRUCK BANDA ACHE, INDONESIA WITH A RUNUP HEIGHT OF 51 METERS, AND THAILAND WITH A RUNUP HEIGHT OF 19.6 METERS - THIS RESULTED IN APPROXIMATELY 300,000 DEATHS

CASE STUDY 1: 2004 INDIAN OCEAN AFTER THE TSUNAMI TOOK PLACE, A TRENCH WAS DUG ON THE COAST OF SOUTHWEST THAILAND TO STUDY THE DEPOSITS SCIENTISTS FOUND THAT THE 30-40CM THICK DEPOSIT WAS COMPOSED OF MEDIUM TO COARSE SAND, AND FORMED A SINGLE LOBE-SHAPED SEDIMENTARY BODY APPROXIMATELY 15M LONG AT 40M WIDE LAYERS IN THE DEPOSIT HAD VARYING MUD CONTENT, WHICH WAS DEPENDENT ON THE PERIOD OF THE FOUR WAVES

CASE STUDY 2: PAPUA NEW GUINEA JULY 17, 1998 FORMED BECAUSE OF A MAGNITUDE 7 AND A LARGE NEARBY SUBMARINE LANDSLIDE THREE MAIN WAVES EACH WITHIN FIVE MINUTES OF EACH OTHER THE SECOND AND THIRD WAVES ARRIVING AFTER BEFORE THE PREVIOUS HAD FULLY RECEDED MAXIMUM WATER LEVELS REACHED 15 METERS SANDY BED WAS DEPOSITED AS A THIN CONTINUOUS SHEET OVER SEVERAL TENS OF KILOMETERS OF COAST EXTENDED 100 METERS FROM THE SHORELINE TO LIMIT OF INUNDATION INUNDATION:: HORIZONTAL MEASUREMENT OF THE PATH OF THE TSUNAMI NORMALLY GRADED

SUMMARY WHY STUDYING TSUNAMIS IS IMPORTANT HOW A TSUNAMI IS CREATED HYDRODYNAMIC PROPERTIES DEPOSITIONAL FEATURES SIMILARITIES AND DIFFERENCES BETWEEN COASTAL STORMS AND TSUNAMIS DIFFERENT CASE STUDIES

BIBLIOGRAPHY MORTON, R.A., GELENBAUM, G. AND JAFFE, B.E. 2007. PHYSICAL CRITERIA FOR DISTINGUISHING SANDY TSUNAMI AND STORM DEPOSITS USING MODERN EXAMPLES, SEDIMENTARY GEOLOGY, 200, 184Â 207. MATSUMOTO, M., NARUSE, H., FUJINO, S., SURPHAWAJRUKSAKUL, A., JARUPONGSAKUL, T., SAKAKURA, N. AND MURAYAMA, M. 2008. TRUNCATED FLAME STRUCTURES WITHIN A DEPOSIT OF THE INDIAN OCEAN TSUNAMI: EVIDENCE OF SYN-SEDIMENTARY DEFORMATION, SEDIMENTOLOGY, 55, 1559-1570.

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