Pollen study confirms legend

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A scientist at Simon Fraser University is searching through buried plant remains for signs of earthquakes and other catastrophic events from the distant past.

Rolf Mathewes uses analysis of fossil pollens to determine the frequency of seismic activity during the last few thousand years. But uncovering evidence of past earthquakes, scientists should be able to determine more accurately the likelihood of future ones, he says.

Studies of plant remains may also back up Native Canadian legends. During land claim hearings for the Gitksan-Wet'suwet'en people of British Columbia, underwater sediments interpreted by Mathewes lent support to an 'oral history' describing a landslide long ago. The tale, which had been kept alive for hundreds of generations, was used to justify the Gitksan claim to land in B.C.

In 1986, the Gitksan tribe contacted Mathewes for help in justifying its claim to 57,000 hectares of land in northwest B.C. To prove it was a long-time occupier of the land, the tribe collected oral histories dating back thousands of years.

The legends included the tale of a huge 'Medeek' or mythological grizzly bear, which had raced down the side of a mountain near Hazelton, tossing trees into the air. When it jumped into the Skeena river, water levels in the nearby "Lake of the Summer Pavilion' rose.

To the people building the case, this tale described a landslide which had blocked a lake outlet stream. "There's evidence of a series of landslides in the region. And you clearly see a flooded area in the valley bottom. This marshland backs up into Seeley Lake, and it looks like the lake level at one time in the distant past rose very quickly."

To confirm that the flooding had actually been caused by a landslide, two independent studies were conducted. A geologist identified which landslide had come by the closest to the Skeena River. By analyzing wood that had been uprooted, he estimated its age about 3,500 years.

This research helped the Gitksan tribe convince the B.C. Supreme Court that its oral histories are substantially correct. Although it lost the claim, the tribe is currently appealing the decision to the Supreme Court of Canada. However, the case illustrates

the value of taking oral histories seriously, Mathewes says.

Meanwhile, Mathewes began sampling bottom sediments in the deepest part of Seeley Lake. The most common finding was a "fine-grained, cheesey mud". However,

a thin band of sandy clay was also present about 1.5 metres into the mud. On top of the clay lay birch seeds, many unidentified plant bits, and the remains of aquatic life plants that only grow in shallow areas. An examination of these fossils showed they were deposited about the same time as the landslide.

Each tremors and other dramatic geographical events in the pst are often represented by sudden changes in the character buried vegetation, says Mathewes. When a major earthquake occurs, "the strain tends to buckle the land or cause it to settle." Although the resulting change in elevation may be less than a foot, for plant communities in low lying areas that's enough to create havoc.

In the Fraser River deltas, for example, plant communities of vastly different kinds are found in relatively close quarters. At the boundary between salt water and fresh water there are salt marshes. At slightly higher elevation, the marshes give way to inter-tidal grasslands and swamps, Mathewes says. And in areas of good drainage, there are forests.

A sudden shift in elevation can produce several different effects.

"A salt marsh might turn into a swamp and a swamp into dry forest, or the other way around."