Giant Avalanches and Mega-tsunami (not)

N coast of E. Moloka‘i

WHAT CAUSED THE HUGE PALI? FAULTING? MARINE EROSION? VALLEY EROSION? SOME COMBINATION OF THESE? Dana (1890) “Thus such precipices are rather the rule in the Hawaiian group; and if seashore erosion is not the origin, - as many facts from the islands of the Pacific appear to show, - fractures and subsidence must be.

Formation of a cliff (that might be, or has been, mistaken for a fault or avalanche scarp) by coalescence of amphitheater-headed valleys (Modified from Stearns & Vaksvik 1935)

“Topographic evidence indicates the presence of two large submarine landslides on the slope of the Hawaiian ridge northeast of Oahu. One slide is more than 150 km long and moved on a slope with an overall gradient of about 2 degrees.” (Moore 1964) “However, recent detailed work on the topo- graphy of the region…does not support this hypothesis. The undersea hills are very large as compared with the bumps on known land- slides, and some of them have forms charac- teristic of volcanic cones. The Tuscaloosa (also called Tuscarora) Seamount, for example, has a height of about 6,000 feet above the surrounding sea floor, and its general form… suggests that it is probably a guyot…” (Macdonald and Abbot 1970)

(Moore 1964)

(Moore et al. 1989) GLORIA side-scan sonar data (smooth surfaces show up as dark, rough surfaces show up as bright) (Moore et al. 1989)

(Moore et al. 1989)

17 large landslides in principal Hawai‘i region Represents ~6 million yrs (= 1 every 350,000 yrs) Two Kinds: slumps (prolonged, progressive formation) and catastrophic debris avalanches Off-shore failure accelerates on-shore erosion Debris avalanches are likely to produce huge tsunami locally, but Would they be Pacific-wide?

Nu‘uanu Debris Avalanche Ka‘ena Slump Wailau Slide Wai‘anae Slump (slide by John Sinton)

actual avalanche scarps obvious cliffs after Moore (1964)

Profiles through E. O‘ahu showing landslide blocks (~3x vertical exaggeration) Landslide headwall E. O‘ahu - restored Wai‘anae Diagrams by Moore and Clague [2002], slide by John Sinton

potential giant avalanche slide-plane?

A deposit of coral and basalt boulders resting ~conformably on basalt flows, ~100 m above sea level, S. coast of Lana‘i -

Moore and Moore (1988): the Hulopoe Gravel was deposited by giant waves (megatsunami) generated by large submarine landslides. Moore and Moore (1988) also speculated that other high-level deposits elsewhere in Hawai‘i might also be explained with this mechanism (slide by John Sinton)

Rubin et al. (2000) dated carbonates from the deposit: Age correlates with stratigraphic height None of the clasts indicate a 105 ka “event” (slide by John Sinton)

The deposit is too old to have been produced from the Alika Slide The presence of internal stratigraphy indicates it is not the product of a singe event (or wave) These results favor deposition from rising and falling sea level over a period of more than 100,000 years (scenario B). Rubin et al. [2000] (slide by John Sinton)

Three of the disconformities are associated with truncated paleosols Felton et al. [2000] recognized up to 14 different beds in the unit, and 8 different disconformities in the 9-m thick type section. Three of the disconformities are associated with truncated paleosols The deposition of the Hulopoe Gravel was not continuous. At least one bed is clearly alluvial (slide by John Sinton)

The boulders are sorted by age: Different sea levels? Multiple tsunami? Enough time between events To develop soil? ~1 m

Photo by Peter Mouginis-Mark, HIGP/SOEST

Ward SN (2001) Landslide Tsunami. J Geophys Res 106: 11201-11215

Ward SN (2001) Landslide Tsunami. J Geophys Res 106: 11201-11215

Ward SN (2001) Landslide Tsunami. J Geophys Res 106: 11201-11215

Ward SN, Day S (2001) Cumbre Vieja Volcano – Potential collapse and tsunami at La Palma, Canary Islands. Geophys Res Lett 28:3397-3400

Ward & Day (2001) http://geology.com/news/images/canary-islands-la-palma.jpg

http://www.geo.arizona.edu/%7Eandyf/LaPalma/1949-Faults.jpg

http://geology.com/news/2005/09/atlantic-ocean-tsunami-threat.html

http://www.lapalma-tsunami.com/reactions.html

A web version of this is at http://www.drgeorgepc.com/TsunamiMegaEvaluation.html

http://www.tsunamisociety.org/PressReleases.html

(Lamb et al. 2007)

Giant avalanches as a mechanism to give a head start to large amphitheater-headed valleys: Kohala The giant avalanche speeds up erosion and thereby enhances stream piracy. (Lamb et al. 2007)

(Lamb et al. 2007)

CREATION OF A SUBMERGED TERRACE REPRESENTING THE END OF THE THOLEIITE SHIELD

Avalanche scar (shortly before the end of tholeiite shield- building) Coastline when tholeiite shield stopped erupting (~1.5 million years ago) Kalaupapa (rejuvenation) ~350,000 years old Coastal terrace: wave-cut platform + reef, from pre- Kalaupapa low sea-level Time (~420,000 or ~350,000 years ago) Clague & Moore (2002)