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Effects of the March 1964 Alaska earthquake on the hydrology of south-central Alaska: Chapter A in The Alaska earthquake, March 27, 1964: effects on hydrologic regimen

Professional Paper 544-A

This report is Chapter A in The Alaska earthquake, March 27, 1964: effects on hydrologic regimen. For more information, see: Professional Paper 544.
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Abstract

The earthquake of March 27, 1964, greatly affected the hydrology of Alaska and many other parts of the world. Its far-reaching effects were recorded as water-level fluctuations in gages operated on water wells and streams. The close-in effects were even more striking, however; sediment-laden ground water erupted at the surface, and even ice-covered lakes and streams responded by seiching. Lake and river ice was broken for distances of 450 miles from the epicenter by seismic shock and seiche action. The surging action temporarily dewatered some lakes. Fissuring of streambeds and lakeshores, in particular, caused a loss of water, and hydrologic recovery took weeks in some places. Landslides and snow avalanches temporarily blocked streams and diverted some permanently. The only stream or lake structures damaged were a tunnel intake and two earthen dams. The winter conditions-low stages of water and the extensive ice cover on lakes and streams-at the time of the earthquake greatly reduced the damaging potential. Ground water was drastically affected mostly in unconsolidated aquifers for at least 160 miles from the epicenter. Within 100 miles of the epicenter, vast quantities of sediment-laden water were ejected in most of the flood plains of the glaciofluvial valleys. A shallow water table and confinement by frost seemed to be requirements for the ejections, which were commonly associated with cratering and subsidence of the unconsolidated material. Subsidence was also common near the disastrous submarine landslides, and was probably caused by loss of water pressure and by lateral spreading of sediments. Effects on ground water in bedrock were not determinable because of lack of data and accessibility, particularly within 50 miles of the epicenter. Deep aquifers in unconsolidated sediments, which in most areas are under high hydrostatic pressure, were also greatly affected. Postearthquake water levels for a year were compared with long-term prequake levels to show permanent changes in an aquifer system. At Anchorage and in parts of the kenai Peninsula, artesian-pressure levels dropped as much as 15 feet. These lower pressures were probably caused either by grain rearrangement which increased the porosity within the aquifer or by a displacement of material that allowed water to discharge more freely at the submarine terminus of the aquifer. Seismically induced pressure on ground water was instrumental in causing most of the disastrous slides. Water quality was not changed except for temporary increases in turbidity in wells and streams. The sediment load in streams during the April spring run-off appeared to be greatly increased over previous years.

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Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Effects of the March 1964 Alaska earthquake on the hydrology of south-central Alaska: Chapter A in The Alaska earthquake, March 27, 1964: effects on hydrologic regimen
Series title:
Professional Paper
Series number:
544
Chapter:
A
Year Published:
1966
Language:
English
Publisher:
U.S. Government Printing Office
Publisher location:
Washington, DC
Contributing office(s):
Menlo ParkCalif. Office-Earthquake Science Center
Description:
p. A1-A28
Larger Work Type:
Report
Larger Work Subtype:
USGS Numbered Series
Larger Work Title:
The Alaska earthquake, March 27, 1964: effects on the hydrologic regimen (Professional Paper 544)
Number of Pages:
28
Country:
United States
State:
Alaska
Additional Online Files(Y/N):
Y