Tsunami deposits beneath tidal marshes on Vancouver Island, British Columbia

Abstract

Research Article| October 01, 1994 Tsunami deposits beneath tidal marshes on Vancouver Island, British Columbia JOHN J. CLAGUE; JOHN J. CLAGUE 1Geological Survey of Canada, 100 West Pender Street, Vancouver, British Columbia, Canada V6B 1R8 Search for other works by this author on: GSW Google Scholar PETER T. BOBROWSKY PETER T. BOBROWSKY 2Geological Survey Branch, Ministry of Energy, Mines, and Petroleum Resources, 1810 Blanshard Street, Victoria, British Columbia, Canada V8V 1X4 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN J. CLAGUE 1Geological Survey of Canada, 100 West Pender Street, Vancouver, British Columbia, Canada V6B 1R8 PETER T. BOBROWSKY 2Geological Survey Branch, Ministry of Energy, Mines, and Petroleum Resources, 1810 Blanshard Street, Victoria, British Columbia, Canada V8V 1X4 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1994) 106 (10): 1293–1303. https://doi.org/10.1130/0016-7606(1994)106<1293:TDBTMO>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation JOHN J. CLAGUE, PETER T. BOBROWSKY; Tsunami deposits beneath tidal marshes on Vancouver Island, British Columbia. GSA Bulletin 1994;; 106 (10): 1293–1303. doi: https://doi.org/10.1130/0016-7606(1994)106<1293:TDBTMO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Thin sheets of sand occur within Holocene mud and peat deposits beneath tidal marshes at Tofino, Ucluelet, and Port Alberni on Vancouver Island, British Columbia. The sand sheets are extensive and have sharp upper and lower contacts. In most cases they consist of moderately sorted, massive sand and silty sand with abundant wood and other plant detritus. At Port Alberni, the thickest sheet has gravel and is graded. The upper two sand sheets in the Tofino-Ucluelet area, and possibly the third, are also present at Port Alberni.Eyewitness accounts and 137Cs analysis suggest that the uppermost, thinnest sand was deposited by the tsunami triggered by the great Alaska earthquake in 1964. The next oldest sand sheet has been radiocarbon dated at <500 yr old. At Tofino and Ucluelet, it sharply overlies a former marsh surface that probably subsided suddenly during a large earthquake; the sand was deposited by a tsunami generated by this earthquake. The third sand sheet at Tofino is 500-800 yr old. The tsunami that deposited it may have been caused by the penultimate, great subduction earthquake in southern Alaska, a previously unrecognized earthquake on the Cascadia subduction zone, a great earthquake elsewhere in the North Pacific, or a large submarine landslide.Our data suggest that large tsunamis have struck the southern British Columbia coast several times during the late Holocene and that some were much larger than the 1964 tsunami, which caused about $10 million damage (1964 Canadian dollars) to communities on Vancouver Island. Because such tsunamis can be expected in the future, they pose a hazard to people and property in some coastal areas. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.