Activity— Cascadia Tsunami Geology Photo In North America, the remains of sunken marshes and the writings of samurai, merchants, and peasants. Their forests tell of Pacific Northwest earthquakes that lowered precisely dated accounts provide evidence that the most coasts by a meter or more. Sheets of sand (exposed outcrop recent of the Northwest’s great earthquakes occurred in images below and described on next page) on the buried on January 26, 1700 at about 9:00 PM, and that this marsh and forest soils testify to associated tsunamis that earthquake attained magnitude 9. Thanks to these and ran across the freshly lowered landscape. In Japan, too other discoveries, great earthquakes and their tsunamis can far from North America for its parent earthquake to be no longer take the Pacific Northwest by complete surprise. felt, an orphan tsunami three centuries ago registered in Not just a dirt-layer outcrop............................. but clues to a remarkable geologic story! LEFT: Poster-size photo from CEETEP Workshop of a cut bank where there is evidence of tsunamis, revealed by Brian Atwater.. RIGHT: Brief descriptions of what is visible in the layers as keys to processes (see next page). A Word document with labels is in this folder for students. The Orphan Tsunami (Atwater and others, 2005) is reviewed by G.Pararas-Carayannis*: “A section of the book summarizes and interprets the significance of extensive geological findings and purported paleotsunami deposits (sand layers covering peaty soils) found by geological investigations along the shores of northern California, Oregon, Washington and British Columbia, as evidence that tsunamigenic earthquakes have occurred throughout geologic time along the Cascade Subduction Zone.” (* From: Science of Tsunami Hazards, Vol. 24, No. 1, page 51 (2006)) Background Science Standards (NGSS; pg. 287) For a “Who done it?” story of the field research behind discovering the M9 earthquake & tsunami of 1700, read the first 25 pages of Orphan Tsunami • From Molecules to Organisms— (page 18 on next page; link to book below. Structures and Processes: MS-LS1-8 • Motion and Stability—Forces­­ and Procedure: Interactions: MS-PS2-2 Students observe large photo and try to decipher what the photo is showing. • Energy: MS-PS3-5 They need prerequisite knowledge of the mechanics of tsunamis with the down • Waves and Their Applications drop and incoming waves. After discussion, students then place pre-cut pieces in Technologies for Information from Tsunami Cutbank Photo Cutouts.doc (in this folder) and place on large Transfer: HS-PS4-1 tsunami photo to indicate the different things that the photo is showing. • Earth’s Systems: HS-ESS2-1, MS- ESS2-2, HS-ESS2-2, MS-ESS2-3 Resources on this DVD for the tsunami of 1700 • Earth and Human Activity: HS-ESS3-1, MS-ESS3-2 ANIMATION relevant to this topic are in the folders: 3. Cascadia Earthquakes & Tsunamis > 2. ANIMATIONS Cascadia Earthquakes & Tsunamis > ElasticRebound_Subduction.mov BOOK: 3. Cascadia Earthquakes & Tsunamis > 5. OTHER > Orphan Tsunami-Atwater Or on the internet: http://pubs.usgs.gov/pp/pp1707/ VIDEO: 9-minute OPB special about evidence for Cascadia tsunami: 3. VIDEOS Cascadia Earthquakes & Tsunamis > TsunamiUpdate_OregonFieldGuide_OPB.mov Or on the internet: http://www.opb.org/programs/ofg/segments/view/1715?q=tsunami e-binder for 2014 CEETEP workshop 207 Page 18 exerpt from The Orphan Tsunami of 1700: Japanese Clues to a Parent Earthquake in North America Sand sheets 地層中の砂層 Chilean counterparts Tsunamis overran newly dropped land along Cascadia’s Pacific coast. THE TSUNAMI associated with the giant 1960 Chile coated plains beside Miyako Bay with alternating layers of earthquake deposited sand in Chile. The deposit was noted sand and silt. The layers probably represent several of the SIGNS OF CASCADIA TSUNAMIS WHILE MAPPING Cascadia’s signs of sudden subsidence, soon afterward at several northern sites. Additional dozens of 1960 tsunami waves recorded by the Miyako 130° 120° geologists in the 1980s and 1990s found associated evidence examples were documented decades later near Maullín, tide gauge. Those waves were numerous because, like the for tsunamis. That evidence consists of sand sheets beside where tsunami sand had settled on subsided pastures. Cascadia tsunamis simulated on pages 37, 74-75, and 103, B.C Sand sheets bays and river mouths (dots on map, left). The sand came 50° Likewise in Japan, on the far side of the Pacific, the the 1960 Chile tsunami reflected off shorelines and from the sea; it tapers inland and contains the microscopic 1960 tsunami deposited sand onshore. For example, it resonated in bays. siliceous shells of marine diatoms. Beside muddy bays the Wash. + Puget Sound sand alternates with layers of mud (photos below) that Seaward Willapa Bay probably settled out in lulls between individual waves in a In Chile In Japan edge of tsunami wave train (modern example, opposite). Cascadia At most sites, the sand arrived just before tidal mud TSUNAMI DEPOSIT NEAR MAULLÍN TSUNAMI DEPOSIT BESIDE MIYAKO BAY subduction Oregon zone began covering a freshly subsided soil (cartoons below). Sand sheet 50-170 m inland from bay Neither a storm nor a tsunami of remote origin explains this Tidal marsh 6 m Tsunami crest 5.5 m above mean sea level Crescent City coincidence with subsidence. The simplest explanation is a Field Beach ridge Calif. tsunami from an earthquake in which a tectonic plate, in a 40° Pacific Ocean Bay seismic shift, abruptly displaces the sea while lowering the 0 adjoining coast. The resulting tsunami then overruns the N 10 cm lowered land (cartoon, p. 10). 10 cm SEDIMENT 0 500 km COLUMNS Pasture soil Sand sheet deposited by 1960 tsunami; later etched by high tides A TSUNAMI LAYS DOWN A SHEET OF SAND Silt and sandy silt Deposited by 1960 tsunami Fine sand Before Minutes to hours Centuries after WAVE TRAIN AT TALCAHUANO TIDE GAUGE Soil earthquake after earthquake earthquake First wave crest Land subsides Mud deposited by tides since WAVE TRAIN AT MIYAKO TIDE GAUGE 40 minutes during earthquake Sand-laden tsunami 1700. Contains coarse silt but 40 minutes (diagram, p. 10) overruns subsided lacks sand except just above a after earthquake First wave 22.6 hours after earthquake landscape. subsided, buried soil. Mud thickness, 80 cm 66 hr hr 6 hr Marsh Sand sheet T 1 m High H G Detail below I 1 m Low tide E tide H TIME 1200 G.M.T., 23 May 1960 (in both marigrams) Buried soil of marsh that Gray line: gauge disabled; subsided in 1700 TSUNAMI SOURCE extremes read on tide staff TSUNAMI HEIGHTS BESIDE MIYAKO BAY (location, p. 51) 75°W 142°E Inland Grass bent inland by incoming tsunami Talcahuano tide gauge 1960 SAND SHEETS from tsunamis of great Pacific Miyako tide tsunami Cascadia earthquakes have been identified along Ocean gauge y Puerto Saavedra a height (m) B n ea c Cascadia’s Pacific coast (compilation by Peters TIDAL MUD O Río Lingue Sand sheet o and others, 2003) and at northern Puget Sound 5 cm 40°S deposited by ak 5-6 m (Williams and others, 2005). Some cover Río Trufun Sand sheet, y ific c 1960 tsunami Mi a 4-5 archaeological sites (p. 20-21) and the floors of Maullín above P 3-4 coastal lakes (Hutchinson and others, 1997). (located at 2-3 Constituents include microscopic marine fossils Kanahama, (Hemphill-Haley, 1996). Sand sheets in British Approximate area of sea-floor uplift 1-2 Grass tuft p. 56) Columbia record Alaskan waves of 1964 in addi- and subsidence during 1960 Chile 39° 45° N tion to the 1700 Cascadia event (Clague and mainshock (p. 10). This deformation 35’ others, 2000). Onshore limit of generated the tsunami. N 1960 tsunami (p. 56) 0 2 km A SMALL TSUNAMI on April 25-26, 1992, in BURIED MARSH SOIL N northern California, provides further evidence 0 500 km that the Cascadia subduction zone generates Niawiakum River, Willapa Bay tsunamis of its own. The parent earthquake, of Sandy layer, each the likely record of an onrushing wave The parent earthquake took place 1710-1715 G.M.T., 22 May 1960 G.M.T., Greenwich Mean Time magnitude 7.1, probably broke the Cascadia (Oyster locality of Atwater and in the tsunami train that began the evening of January 26, plate boundary near its southern end. The Hemphill-Haley, 1997) 1700 (inferred timing, p. 42-43). The sandy layers SAND SHEETS were noted by Wright and Mella (1963, p. 1371, 1372, 1389) AT MIYAKO BAY the 1960 tsunami deposits contain microscopic marine tsunami crested 0.5 m above tides at Crescent fossils (Onuki and others, 1961) in addition to the multiple layers illustrated alternate with mud that probably records the slack water of and, near Maullín, by Cisternas and others (2005). Tide-gauge data redrawn City, where it lasted eight hours (Oppenheimer from Sievers and others (1963, sheet 3). Tsunami source inferred from land- above (redrawn from Kitamura and others, 1961b). Details on the marigram, crested waves. and others, 1993). level changes mapped by Plafker and Savage (1970). p. 46; sources for the mapped tsunami heights, p. 55. VIDEO: One-hour talk by Brian Atwater about the quest for tsunami answers in the Pacific NW: http://www.iris.edu/hq/programs/education_and_outreach/distinguished_lectureship/past_speakers/atwater/video18 THE ORPHAN TSUNAMI OF 1700 Unearthed earthquakes 19 208.