Tsunamis Always a Danger to Hit Ocean Beach

By Andy Isaacson

As the Indian Ocean communities devastated by last month's earthquake-induced tsunami mourn their dead and slowly rebuild, Bay Area residents cannot help but wonder: Could it happen here? The short answer is yes, it is possible, although the Pacific Ocean tsunami warning system would help save lives.

In the wake of the tsunami, researchers are paying careful attention to the Cascadia subduction zone, an undersea fault 50 miles off the California coast that has similar patterns as the fault that triggered the earthquake off Sumatra. 

In 1700, the fault generated a powerful, 9.0 rumble in Alaska that sent tsunamis across the Pacific Rim. Since then, the fault has remained "locked" - building up energy for a future mega-quake, which seems to occur every few hundred years. Over the past 150 years, less seismically intense fault lines have generated around a dozen tsunamis - including the 1964 "Good Friday" earthquake that sent recorded waves of more than six feet onto San Francisco streets.

State and local officials have devised evacuation routes from San Francisco's most at-risk areas - the neighborhoods bordering Ocean Beach - and a network of 50 warning sirens are scattered throughout the City. Proper evacuation is common sense - if you are on the beach or on low-lying coastal ground and feel an earthquake that lasts more than 20 seconds, head to higher ground. Tsunamis travel like ripples in a pond: Don't assume the first wave is the last.

While tsunamis are capable of wreaking immediate destruction on San Francisco, a less dramatic yet perhaps equally damaging phenomenon has scientists and environmental policy advocates concerned - rising oceans due to the effects of global climate change.

As a result of fossil fuel emissions from power plants, buildings and gas-powered vehicles, temperatures have risen and polar ice has melted. The 2,500-member Intergovernmental Panel on Climate Change has reported a four-to-seven-inch sea level rise during the past 100 years, and says average Earth temperatures could increase by as much as 10 degrees during the 21st century.

Researchers predict a variety of ecological and economic impacts that warming, and corresponding sea level rises, could have on the San Francisco Bay Area. Increased temperatures would mean fewer freezing days and a halving of winter snow accumulation. More water would flow in the winter, causing flooding, and less would be available during the summer. Greater storm activity could increase beach and cliff erosion and roads, pipelines, transportation, underground cables and sewage systems could be severely stressed or overwhelmed. Additionally, low-lying areas, such as San Francisco International Airport which is built on a wetland, would be at high risk of flooding. Warming could also make tick-borne Lyme disease more prevalent and expand the range of mosquito-borne diseases.

Last fall, Mayor Gavin Newsom announced an ambitious plan outlining steps that local government agencies, residents and businesses could take to reign in San Francisco's greenhouse gas emissions. These include relying on "greener" alternative fuels - such as natural gas and bio-diesel - greater public transit use and increased use of solar and wind energy.