Friday, November 5, 2010


Adak, Alaska is a small island extending towards Russia in the Aleutian Island region. It is the westernmost municipality in the United States and the southernmost city in Alaska. The 2009 census showed a population of 361 people and the city has a total area of 127.3 square miles. They sit on top of a huge cliff so to speak, just off the coast the ground drops off to a small ledge and then drops down again. These earthquakes appear to be happening deep in the waters surrounding this area. Most have been located on the shelf half way to the bottom.

The earthquakes started 2 days ago and they have had 40 so far with a magnitude of 3.0 or higher. The strongest was a 5.2 at 5am CST today, Friday November 5th, 2010. These started on Wed. with a 5.0 & 5.1 right after each other.. There is no telling when these will stop as the ground continues to shake. The last quake since this blog was made was a 4.4 at 12:25pm CST today...

The Aleutian Islands were historically occupied by the Unanga, more commonly known now as the Aleuts. The once heavily-populated island was eventually abandoned in the early 19th century as the Aleutian Island hunters followed the Russian fur trade eastward, and famine set in on the Andreanof Island group. However, they continued to actively hunt and fish around the island over the years, until WWII broke out. Adak Army installations allowed U.S. forces to mount a successful offensive against the Japanese held islands of Kiska and Attu. After the war, Adak was developed as a naval air station, playing an important role during the Cold War as a submarine surveillance center. Large earthquakes rocked the island in 1957, 1964 and 1977.
At its peak, the station housed over 6,000 naval and Coast Guard personnel and their families. In 1994, the base was downsized, and both family housing and schools were closed. The station officially closed on March 31, 1997. The Aleut Corporation purchased Adak's facilities under a land transfer agreement with the Department of the Interior and the US Navy/Defense Department. This agreement was finalized in March, 2004. About 30 families with children relocated to Adak in September 1998, most of them Aleut Corp. shareholders, and the former high school was reopened at that time as a K-12 institution. The community incorporated as a second-class city in April 2001. Substantially all of the infrastructure and faciltities on Adak are owned by Aleut Corporation, who is currently developing Adak as a commercial center via their subsidiary companies. For example, properties in active use are leased by Adak Commercial Properties, LLC.
Since World War II, the U.S. Navy and Coast Guard developed facilities and recreation opportunities at Adak. At its peak, Adak had a college, a McDonalds restaurant, movie theater, roller skating rink, swimming pool, ski lodge, bowling alleys, skeet range, auto hobby shop, photo lab, and racquetball and tennis courts. A new $18-million hospital was built in 1990, just seven years prior to the closure of the station. By March 2003, six years after the closure of the station, most of these facilities had closed. For a time, Adak became a virtual ghost town, with its buildings showing little sign of wear or disuse. In recent years, preventing trespassing in and vandalism of the unoccupied facilities has become an ongoing struggle for the Aleut Corp. The harsh Aleutian wind and weather has also played a part, all but destroying the majority of facilities remaining on Adak that are not in active use.

 During the past century, four large and well documented tsunamis were generated in the waters off the Alaskan coast. These include the 1946 and 1957 Aleutian events, the 1958 Lituya Bay event, and the 1964 Alaskan event. While all four tsunamis were produced by seismic activity, the intensities, processes of generation (ie. landslide vs. tectonic), and areas of affected coastline differ for each. 


The earth's most active seismic feature, the circum-Pacific seismic belt, brushes Alaska and the Aleutian Islands, where more earthquakes occur than in the other 49 States combined. More than 80 percent of the planet's tremors occur in the circum-Pacific belt, and about six percent of the large, shallow earthquakes are in the Alaska area, where as many as 4,000 earthquake at various depths are detected in a year.
Early reports of earthquakes in Alaska are fragmentary. The first event in this incomplete record occurred on Sanak and Shumagin Islands, south of the Alaska Peninsula, in July 1788. Apparently no volcanic activity accompanied this event, but the islands of Sanak and Unga and a part of the Alaska Peninsula were inundated by an apparent tsunami (seismic sea wave). The records note, "Some natives lost their lives and hogs drowned."
Instrumental locations of earthquakes since about 1900 indicate that earthquakes in Alaska center principally in two seismic zones. The most important is the Aleutian Island Arc, one of the planet's most active seismic areas, which extends about 2,500 miles, from Fairbanks in central Alaska through the Kenai Peninsula to the Near Islands. It maintains a width of nearly 200 miles throughout most of the zone. The second zone begins north of Yakutat Bay in southeastern Alaska and extends southeastward to the west coast of Vancouver Island.
From 1899 to 1969, eight earthquakes of magnitude 8 or more on the Richter scale have occurred in Alaska. Four caused extensive property damage and topographic changes; four centered in areas with no nearby towns, and, except for being recorded by seismographs, went relatively unnoticed.
The Alaskan earthquake that is outstanding in the memory of most occurred in the Anchorage area on March 27, 1964. The magnitude 8.5 [recalculated to 9.2] shock devastated downtown Anchorage and left homes twisted and broken in the residential section of Turnagain. A tsunami virtually destroyed many of Alaska's coastal towns and spread death and destruction along the west coast of the United States, Hawaii, and Canada.
Since the temblor occurred on Good Friday, a holiday for schools, and at a time when most people were out of office buildings and on their way home from work, few deaths were caused by the earthquake itself. But 122 persons were drowned by the ensuing tsunami waves: 107 in Alaska, 11 in California, and 4 in Oregon.
The Yakutat Bay area of southeastern Alaska experienced one of the notable earthquakes of the last century on September 10, 1899. Although this shock was preceded one week earlier by a magnitude 8.2 earthquake, most of the effects were associated with the September 10 event which was rated magnitude 8.6 on the Richter scale.
Both of the shocks were felt at villages over 400 miles from Yakutat Bay. The only settlement in the area was Yakutat village, over 30 miles form the Bay. The shaking there on September 3 was described by eye-witnesses at "violent, and impossible to stand without holding on to something." Prospectors in Disenchantment Bay, an arm of Yakutat Bay, described the September 3 shock as "slight," compared to the earthquake a week later. Eight men camped near Disenchantment Bay during this violent shock barely escaped with their lives. Behind one camp the water in a small lake left its banks and swept down toward the beach, carrying masses of rock with it. The prospectors described a wave immediately afterward to be 20 feet high; it washed inland over the beach and swept everything away but a few provisions and one boat. All managed to escape to Yakutat.
There is little doubt that changes in land level, chiefly uplifts, occurred at the time of these earthquakes. During June 1899, three months before the shocks, the Harriman Scientific Expedition visited the region to study glaciers and did not report unusual land-level changes. Also, photographs taken in 1895 showed coasts and islands as they had been previously mapped. A field investigation in this area was undertaken in 1905 by a U.S. Geological Survey party. They reported the largest uplifts in land ranged from 30 feet to about 47 1/2 feet on the west coast of Disenchantment Bay. Changes of 17 feet or more affected a large area, and, in a few cases, 1 to 7 foot depressions occurred. 

In October 1900, a magnitude 7.9 earthquake was felt from Yakutat Bay to Kodiak, and probably farther westward. On Kodiak Island chimneys were downed, and a man was thrown from his bed. The shock probably centered near Cape Yakataga in southeastern Alaska. Property damage was very moderate for such a great shock, due to the sparsity of population.
The Andreanof Island sustained a magnitude 8.8 earthquake in March 1957 that caused very severe damage on Adak and Unimak Islands. A damaging tsunami was generated, and a wall of water 40 feet high smashed the coastline of Scotch Cap on Unimak Island. Sand Bay, near Adak, reported 26 foot waves inundated its shores.
On Adak, this earthquake destroyed two bridges, damaged some housed, and left gaping cracks in the road. Some cracks were reportedly 15 feet wide, but this is probably an error. At Umnak, part of a dock was destroyed, a cement mixer turned upside down, and other heavy equipment was scattered about. In addition, Mount Vsevidof erupted after being dormant for 200 years. At Sand Bay, the tsunami waves washed away several buildings and damaged oil lines. Millions of dollars in property damage occurred in Hawaii and Japan as a result of the tsunami; minor damage was sustained in southern California and in Central America. This earthquake initiated a series of aftershocks that extended more than 700 miles along the southern edge of the Aleutians.
During the period 1899 to 1969, eight great earthquakes occurred in Alaska, numerous major earthquakes (magnitude 7 to 7.9) centered in the State. Thirteen occurred in or near populated regions and caused minor to severe damage - eight in the intensity (Modified Mercalli Intensity scale) VI category; one, intensity VII; three, intensity VIII; and one, intensity XI. Probably 150 or more occurred in uninhabited areas. Some of the more significant shocks are described below.
On July 22, 1937, a magnitude 7.3 earthquake occurred in central Alaska, about 25 miles southeast of Fairbanks, that was felt over most of Alaska's interior, about 300,000 square miles. About ten years later, on October 15, 1947, a magnitude 7.3 shock occurred in the same region. It was preceded by a swarm of shocks, some very minute, others violent.
On April 7, 1958, a magnitude 7.3 shock centered in central Alaska near Huslia. Within a 40 to 50 miles radius of Huslia, cracks in lake and river ice, and many ground cracks and mud flows, were observed. Evidence of pressure ridges, lakes thawing, numerous lakes filled with black slimy mud, and craters 20 feet across and 6 feet deep were reported. Some minor damage to log structures was sustained in Huslia.
The strongest shock since those of September 1899 at Yakutat hit southeastern Alaska on July 9, 1958. It was rated magnitude 7.9 on the Richter scale. Three persons were killed on Khantaak Island, and two were missing and presumed dead after being caught in a huge wave generated by the shock in Lituya Bay.
This magnitude 7.9 shock was felt by residents over 400,000 square miles of Alaska, as far south as Seattle, Washington, and east to Whitehorse, Yukon Territory, Canada.
The largest magnitude earthquake in the central interior of Alaska since October 1947 occurred on October 29, 1968. Rated magnitude 6.5, the shock centered southeast of the village of Rampart, on the Yukon River. This area was badly shaken, but no damage was sustained, since most buildings at Rampart were of log construction. Most residents were frightened from buildings, goods toppled from shelves, and equipment not bolted down shifted. Greatest evidence of the shaking was in the Hunter Creek area near Rampart. Many landslides occurred, most on south-facing slopes. Lake ice cracks were extensive in some areas and were observed some 50 miles from the epicenter in the Minto Lakes area. Ground cracks were noted at Nenana, about 50 miles southeast of Rampart, and plaster cracked and fell. During the first 24 hours after the earthquake, College Observatory recorded over 2,000 aftershocks.
Abridged from Earthquake Information Bulletin, Volume 2, Number 2, March - April 1970.

No comments:

Post a Comment