NOTES : California’s Geologic Hazards (Portions of 19. 4, 18. 3, 10

Part of what makes California an appealing place to live, also means that natural dangers are everywhere. We live in the middle of a plate boundary We have close proximity to the ocean We have close proximity to mountain ranges

1) Earthquakes While the Pacific Plate and the North American Plate create a Strike-Slip fault, there is a tremendous build-up of force This force also creates many other cracks/faults surrounding the plate boundary, which are all active = STRESS FRACTURES

Areas of concern: Bay Area and Los Angeles. Large parts of San Francisco have older homes built on portions of Bay that were filled in by sandy soils in the early 1900’s (land fill).

These areas suffer great damage during earthquakes, because the soil acts like quick sand. . “liquefaction”. When water seeps into the ground from an earthquake, it takes away friction between soil grains. SF and LA are also both densely populated areas!

The near future? . . It has been said that there is a 63% chance that the Bay Area will have a quake of magnitude of 6.7 or higher between 2003-2033 because of all the faults which cross the bay.

2) Landslides The Coastal Ranges are more at risk for landslides than any other area in California, because they generally have fine-particle soils, more moisture, and little to no tree growth. ( This means there are no plant roots to help secure the soil and keep it anchored. )

3) Volcanoes? Mount Shasta and Lassen are the only volcanoes of the Cascade Mountain Range that are in California. Geologists have determined that there is a ¼ chance that Mount Shasta would erupt in a persons lifetime (1786 was the last one) Mt. Lassen erupted last in 1915, so they don’t expect another one for about 10,000 years.

4)Tsunamis Tsunamis originate from an earthquake at another location; usually somewhere across the Pacific Plate such as Alaska, that can get to the California Coast if they are strong/close enough.

The Northern-most part of California is normally the area hit by tsunamis, if any. Crescent City, CA was hit by a tsunami from Alaska in 1964, and another from the Japanese earthquake in 2011

5) Sink Holes Sink holes are depressions in the ground from a collapse due to erosion, or human activity. The erosion can be from dissolving limestone in water, or disintegration of sandstone. The human activity can be from excessive mining or construction.

Our strong, igneous rocks protect us from sinkholes more so than other locations in the US CA tends to get them for human-induced reasons more than natural