1. Education

How Earthquakes Disturb Streams and Groundwater

By

We're all familiar with how buildings respond to earthquakes—they shake and crumble. We know what happens to high ground—it comes down in landslides. We know what low ground does—it suffers liquefaction. But the most widespread effects of earthquakes may happen to water. Tsunamis, which can cause destruction across entire ocean basins, are the foremost example. This article, however, focuses on things that may affect any place on land.

Shaken Streams and Lakes

By their nature, bodies of water respond to seismic waves of the lowest frequencies, and the same earthquake therefore may affect land and water quite differently. An eyewitness on the Colorado River felt the 9 January 1857 Fort Tejon earthquake as a swaying motion of the ground, but reported, "We looked up the river and the water all drawed off of one place and left it dry. Then in a moment all rushed back again foming and tumbling." The Los Angeles Star reported that "in the river the water rushed violently to one bank and then back again, the motion being repeated several times."

In California's Central Valley during the 1857 quake, a witness standing by Tulare Lake wrote that "the lake commenced to roar like the ocean in a storm," and he fled on horseback as fast as he could ride. Returning the next day, he found that "the lake had run up on the land for about three miles. Fish were stranded in every direction and could have been gathered by the wagon-load." This was probably the result of a large seismic seiche, an event that causes a lake to slosh back and forth for hours or days.

When the land moves permanently up or down, the effects on rivers can be profound. The great 1811–12 New Madrid earthquakes in the central United States locally changed the course of the Mississippi River, and Reelfoot Lake formed where dry land had previously been.

Effects on Groundwater

The water underground moves through a delicately balanced environment, as it dissolves minerals in some places and deposits them in others, while the heavy burden of sediments upon it grows or shrinks with the movements related to erosion. Even the very gentle movement of the daily Earth tide can be seen in some water-well records. Earthquake shaking can damage this intricate microstructure of an aquifer and compress it dramatically. Shallow groundwater can be displaced from the ground in sand blows or emerge in streambeds for short periods.

Earthquakes shake water out of the hills, increasing the vertical permeability of the rocks so that the groundwater stored in mountains is released quickly. This is quite a general phenomenon. One example from the 1857 quake was reported by the Los Angeles Star: "On a range of hills, about fifteen miles from the coast, in the district of San Fernando, we understand that a surveying party have discovered quite a large stream making out of the mountain and down a cañon, where, to their knowledge and complete satisfaction, not to say to their sorrow, no water was running or could be found previous to the earthquake." Streamflow returns to normal over a period of months, and the mountains slowly recharge until the next big quake.

Geothermal areas with their populations of thermal springs are especially prone to earthquake disturbances. The city of Paso Robles was California's first hot-spring resort starting in the 1880s—its main road is named Spring Street—but its historic central spring near City Park dried up after the 1906 San Francisco earthquake. In the years that followed, City Hall and other civic buildings were erected there. Then the 2003 San Simeon earthquake opened the spring again in the City Hall parking lot as well as smaller springs elsewhere along the active Rinconada fault. Dealing with the smelly, acidic fumes and hot water was a headache that took years for the city to deal with by digging a drain to the nearby Salinas River. The spring is still active beneath the rebuilt parking lot.

Disturbances to Wells

Water wells are especially sensitive to seismic influence. Hundreds of kilometers from the 1857 ground rupture, the San Jose Telegraph wrote, "we have heard that the channels of other [artesian] wells, which had become obstructed, and ceased to discharge water, have become re-opened and the subterranean current is now flowing out from the orifice." A San Francisco newspaper story on the earthquake reported that "its effect upon the artesian wells was most singular. The well at the beautiful cottage of Col. A. J. Grayson rose some twelve inches above the usual flow, and then fell suddenly as much below—rose and fell several times and then resumed its usual current. . . . The great well in the city suddenly ceased its flow and now barely runs."

The reported oscillations in the groundwater level were probably related to the lowest-frequency seismic waves, which have periods measured in minutes. Waves of this scale can make the Earth ring like a large soap bubble, as documented in the 2004 Sumatra earthquake. The U.S. Geological Survey has a page on groundwater effects from earthquakes with more detail on that topic.

  1. About.com
  2. Education
  3. Geology
  4. Geologic Hazards
  5. Earthquakes
  6. How Earthquakes Disturb Streams and Groundwater

©2014 About.com. All rights reserved.