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No. 115: Jan-Feb 1998

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The hilina slump a.k.a. "the big crack"

Huge chunks of the Hawaiian Islands have been sliding into the Pacific Ocean for hundreds of thousands of years. (SF#101) Geologists classify these slides as either "slumps" or "debris avalanches." Slumps move just a few inches a year but are prone to bigger, jerky adjustments. Debris avalanches are fast cascades of rocks and soil. In Hawaii, both varieties of movement can involve massive blocks of real estate. In the huge Nu'uanu debris slide, stone blocks 6 miles across tumbled 30 miles out to sea. Both slumps and debris slides may create colossal tsunamis. (Tsunamis are miscalled "tidal waves," but they have nothing to do with tides and do not behave like tides or wind-driven waves.)

When large pieces of the Hawaiian Islands slip into the ocean, the entire Pacific Rim is smashed by the resulting tsunamis. In New South Wales, Australia, there is geological evidence that part of this coast was scoured by a Hawaiigenerated tsunami 100,000 years ago. The postulated wave started out about 375-meters (-mile) high in Hawaii. By the time is reached Australia, it was about 40 meters high. (SF#85)

Worse waves may be on tap. A 4,760 cubic mile chunk of the Big Island (Hawaii) is breaking away at the rate of 4 inches per year. This is the Hilina Slump, and it is said to be "the most rapidly moving tract of ground on Earth for its size." The Hilina Slump can move much faster. At 4:48 AM, November 29, 1975, a 37-mile-wide section suddenly dropped 11 feet and slid seaward 26 feet. The result was a magnitude-7.2 quake and a 48-foot-high tsunami. This was a minor of the slump. If the entire 4,760-cubic-mile block decided to break off, it would probably create a magnitude-9 quake and a tsunami 1,000-feet high. All the coast-hugging cities of the Hawaiian Islands would be swept away. And LOOK OUT Australia, Japan, and California.

(Napier, A. Kam; "Landslide," Honolulu, p. 28, February 1997. Cr. H. DeKalb.)

Comment. Tsunamis travel at jet speeds on the deep, open ocean and have such small amplitudes that ships rarely notice them. Only when they reach shallow water do they slow down and reach monstrous sizes.

From Science Frontiers #115, JAN-FEB 1998. 1998-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:

Quotes

  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987