Multi-Hazard Mitigation Plan: 06. Landslides And Rock Falls

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Chapter 6:Hazard Analysis—Landslides and Rock Falls Figure 6-2. Examples or earthquake-induced rock falls causing road hazard or closure 6.2 Significant Catastrophic Events Giant catastrophic slides have occurred around the major Hawaiian Islands thousands of years ago. At least 15 giant landslides have been identified by United States Geological Survey (USGS)marine scientist with the most recent occurring approximately 100,000 years ago off the Kona coast. Each of these slides has resulted in huge land losses to the islands and resulted in large waves that have carried rocks and sediments as high as 1000 feet above sea level. Although these giant landslides have the potential for enormous loss of life, property and resources, these events are infrequent in human terms, occurring perhaps once every few tens of thousands of years. (USGS,Volcano Watch, 1997) The U.S. Geological Survey (USGS) suggests that we should not be overly concerned about the giant landslides because they are so infrequent (once every few tens of thousands of years) and because"we can do virtually nothing to mitigate such gigantic slides and tsunami- except to follow evacuation routes predetermined by Civil Defense and hope that the tsunami is not too high." (USGS Volcano Watch, 1997) "Worrying realistically means directing our limited resources to the hazardous events most likely to occur-the ones whose effects we now have the ability to mitigate through education and foresight." (USGS Volcano Watch, 1997) A significant landslide mentioned in historical times is a mudflow triggered by the largest earthquake in recorded history in April, 1868. The mudflow killed 31 people in Wood Valley in the Ka'u district. No other landslide event has been mentioned as resulting in any loss of life. 6-3 Hawaii County Multi-Hazard Mitigation Plan