1964 Alaskan Earthquake and Tidal Wave
Justin Taylor
Tidal waves, also known as Tsunamis are large waves of extremely long wavelength generated in a body of water from a major disturbance. As the tsunami crosses the deep ocean, its length from crest to crest may be a hundred miles or more, and its height may be a few feet or less. They cannot be felt aboard a ship or seen from the air in the open ocean. In the deep ocean, the waves will reach speeds exceeding 600 miles per hour. When the tsunami enters shallow water near the coastline the velocity of its wave diminishes and the wave height increases. The tsunami may reach heights of 100 feet or more.
Tsunamis are caused by landslides, volcanic eruptions, objects from space such as meteorites but the most common are earthquakes. During an earthquake seafloor deforms and displaces the overlying water, waves are formed and gravity attempts to regain its equilibrium. The size of the tsunami is directly related to the amount of vertical seafloor deformation. Other factors are shoreline and bathymetric configurations, the velocity of the sea floor deformation, and the water depth near the earthquake epicenter.
NOAA (National Oceanographic and Atmospheric Administration) and the National Weather Service are leaders in tsunami warning systems. They also work closely with the U.S Geological Earthquake Center to monitor seismic activity for tsunami risks. The DART (Deep-ocean Assessment and Reporting of Tsunamis) system is the main tool in early detection and real-time reporting of possible tsunamis. These DART buoys are connected to seafloor pressure recording systems, which send information to satellites and then on to warning centers located in Alaska and Hawaii. The buoys are mainly located along the Aleutian island chain in Alaska; there are also a few offshore of the Pacific Northwest and Hawaii. Also, many coastlines around the world are mapping topography and bathymetric configurations to access risk. One such area is the Aleutian island chain in Alaska, which has begun mapping in the last few years.
Good Friday, March 27,1964 a massive earthquake hits Prince Williams Sound, Alaska. It was rated 9.2 on the Richter scale. The epicenter was 55 miles west of Valdez and 75 miles east of Anchorage. The shaking lasted up to four minutes in surrounding areas. Anchorage was hardest hit, thirty blocks of houses and commercial buildings were destroyed or badly damaged in the downtown area. This was the largest earthquake reported in recent history on the North American continent. It caused the greatest amount of vertical uplift on the seafloor ever measured. The largest wave height was nearly 220 feet; it was in the Valdez inlet at Shoup Bay. Many deaths resulted, 123 people died from Alaska to northern California. It cost well over a hundred million dollars worth of damage. The toll in human life could have been much worse. A few reasons for the small death rate were the low population density in Alaska, the fact that it happened on a holiday and it was 5:30 PM, most people were home.
www.aeic.alaska.edu/Seis/64quake/Alaska_1964_earthquake.html
www.geo.arizona.edu/~/nhartnes/alaska/earth.html