Geography Unit 1, World at Risk Compulsory Case Study 2 - Disaster hotspots: the California coast

The state of California contains nearly 40 million people and has an economy the sixe of a high-income country. However, it suffers from a vast range of hazards, including huge risks from geophysical hazards (especially earthquakes) as well as a range of hydrometeorological hazards such as storms, floods, fog, drought and associated wildfires, and major impacts from the El Nino Southern Oscillation (ENSO). Significant damage to California would be a very significant loss to the USA, as 14% of its GDP comes from California.The hazardous zone is concentrated along the San Andreas fault, which runs parallel to the coast.California is located on the conservative plate boundary between the oceanic Pacific plate and the continental North American plate. Contrary to popular belief, these plates are not moving in opposite directions, but in the same direction, only at different speeds; the Pacific plate is moving north west at a rate of 6 cm per year, whilst the North American plate is moving in the same direction at 1 cm per year. Hazards of the California coast: summaryEarthquakes~Causes: A network of active faults (e.g. San Andreas fault) underlies the Los Angeles region and the San Francisco Bay Area (e.g. Hayward and San Gregoria faults). ~Impacts: The soft basin sediments in Los Angeles lead to rapid shaking. Five major earthquakes were recorded in the last 100 years. The San Francisco Bay Area has experienced several large earthquakes too. River flooding~Causes: Winter storms, especially during El Nino years, lead to floods in the Los Angeles and San Gabriel rivers, exacerbated by deforested hillsides. ~Impacts: Rivers are now heavily channelised, but floods can still take place, usually between October and January. Coastal flooding~Causes: The area around Log Beach, which is subsiding (sinking into the sea), sometimes floods in heavy storms. ~Impacts: Increasing threat with rising sea levels in the future. Drought~Causes: A potential summer problem in Mediterranean climate especially in southern California, but more marked in La Nina years.~Impacts: Exacerbated by lack of water supplies in Los Angeles for rising population. California produces 90% of avocado's grown in the US, but avocado trees won't fruit without regular soakings. Wildfires/bushfires~Causes: As Los Angeles expands into rural areas, wildfires are a major hazard, especially during the dry Santa Ana wind periods. ~Impacts: Likely to be an increasing hazard as people move out to the hills on the fringe of Los Angeles and south of San Francisco. Landslides/mudslides~Causes: Landslides take place in heavy winter storms where hillsides have been burnt by wildfire and eroded. Also a risk along the coast near Malibu and Santa Monica. ~Impacts: A growing risk as climate becomes more unpredictable in all coastal areas. In 1982 18 000 occurred after heavy rains, killing 33 people. Fog and smog~Causes: Advection fog occurs when cool air from cold offshore current drifts inland and meets warm air (especially in summer). Climate conditions combine with car pollution to generate photo-chemical smog, which collects in the basin. ~Impacts: A mega city-wide hazard, especially in late summer and autumn. Probability of occurrence and likely magnitude of earthquakes on the California coast ~North coast: Less than 10% probability, likely magnitude 8. ~Northern East Bay: 20% probability, likely magnitude 7. ~San Francisco Peninsula: 20% probability, likely magnitude 7. ~Southern East Bay: 20% probability, likely magnitude 7.~Southern Santa Cruz Mountains: 30% probability, likely magnitude 6.5. ~Parkfield: 90% probability, likely magnitude 6. ~Cholame: 30% probability, likely magnitude 7. ~Carrizo: 10% probability, likely magnitude 8. ~Mojave: 30% probability, likely magnitude 7.5. ~San Bernadino Mountains: 20 % probability, likely magnitude 7.5. ~San Bernadino Valley: 20% probability, likely magnitude 7. ~San Jacinto Valley: 10% probability, likely magnitude 7. ~Anza: 30% probability, likely magnitude 7. ~Coachella Valley: 40% probability, likely magnitude 7.5. ~Borrego Mountain: Less than 10% probability, likely magnitude 6.5. ~Imperial: 50% probability, likely magnitude 6.5. California is home to the megacity of Los Angeles, San Francisco and San Diego. Much of the coastline is 'crowded' as various land uses compete for prime space. This human-physical interface increases the danger from hazards, and only sophisticated management prevents California from becoming a disaster zone. Recent major events such as the Lomo Prieta earthquake of 1989 led to very few deaths directly, but the shaking caused liquefaction to occur, making buildings sink into the ground and killing 42 people. Nevertheless, California contains an underclass of around 3.5 million people, many of them semi-legal migrants, a large proportion of whom live in hazardous locations.

Disaster hotspots: the California coast