Creatures From the Muck May Help Forecast Earthquakes
Tiny plants and animals suspended in coastal mud flats, salt marshes and freshwater bogs may help tell scientists when the next big earthquake is likely to strike Alaska. According to a British researcher, the microscopic creatures are tipping us off about ground movements that happen before huge earthquakes.
Ian Shennan, a geographer from the University of Durham in England, performs much of his work in rubber boots, exploring the muck where the sea meets the shore. In Scotland, Washington and Alaska, he searches the soil for pollen grains and tiny remains of algae, called diatoms. The varieties he finds tell him how the land has risen or subsided in relation to sea level over the years. For example, when freshwater algae species are abundant in a certain area, he knows the land was above the high tide mark when the algae was alive.
A dramatic change in algae or pollen types means a change in sea level, such as one that happened in Alaska on March 27, 1964. On that day, the Good Friday earthquake rearranged much of Southcentral Alaska. Some areas in Prince William Sound were suddenly 38 feet higher than the day before. At Portage, the ground sunk as much as 8 feet, a fact visible today in the forests of dead trees that were drowned by salt water.
Shennan tracks changes in elevation by finding preserved pollen and algae. In Great Britain, he's tracked the rebound of the land that happened after glaciers melted and relieved the incredible pressure of snow and ice. Over the years, salt-loving algae and plants gave way to species that were less tolerant of salt water. These changes in plant types indicated the land was rising ever so slightly. Mud flats became salt marshes, which eventually changed to freshwater marshes, then to acidic raised bogs, in which all the plants are above the tide line.
The same process is happening along Turnagain Arm in Alaska, just off the Seward Highway. After the drop in 1964, the coastline in Girdwood is being lifted, and that rise above sea level is documented in the remains of ancient plants and algae. Shennan found that when the ground level rises to a certain point in Washington and Oregon, large earthquakes happen. A similar pattern might be happening in Alaska.
By sampling algae and pollen in soil near the coastline at Girdwood and near the mouth of the Kenai River, Shennan found that the land level was rising prior to about 1950, when a gradual fall began. The decrease in elevation accelerated on March 27, 1964 with the sudden eight-foot drop caused by the earthquake.
Shennan thinks the changing of plant and algae communities may be telling scientists something about the way Earth's plates behave before an earthquake. In the 1964 earthquake, the North American Plate slipped past the Pacific Plate below Prince William Sound. The gradual rise measured today in the Turnagain Arm area may be due to the plates locking again and forcing the ground upward.
With pollen and algae providing clues to plate movement, it's up to modern technology to solve the difficult mystery of when the next big earthquake will hit Alaska. While in Fairbanks, Shennan met with geophysicists who track the subtle movements of Earth's plates with Global Positioning System satellites. GPS measurements can perhaps help scientists decipher the clues to earthquake forecasting left behind by ancient pollen and algae.
