Image: University of Delaware

For more than two decades, scientists studying hydrothermal circulation in the water under the seafloor have assumed that the flow is relatively stable. But the far-reaching effects of a small earthquake that occurred last June off the Washington coast are shaking up their view. According to a report in today's issue of the journal Nature, that modest rumble caused 10-fold increases in the flow of fluids in hydrothermal vent systems located nearly five miles away. The temperature of the fluid in the vents, like the one pictured at right, increased as well, and strange temperature oscillations ensued.

"This was not just a local event," says lead author Paul Johnson of the University of Washington."We're continuing to try to determine how much of the ridge system may have changed in reponse to the earthquake. It could be that the fluids over hundreds of miles of midocean ridges are influenced by even moderate quakes."

As it turned out, the altered conditions proved favorable to organisms living on the chemicals in the vent fluids, resulting in greater biological activity. This, in turn, may have caused those mysterious temperature oscillations. An alternative explanation for the oscillations is that the earthquake may have driven cracks in the seafloor down into hotter crustal rocks, releasing heat into the system. The third hypothesis offered in the report is that the new earthquake-induced circulation caused a temporarily unstable temperature. In hopes that new data will help clarify what is going on, Johnson is heading up an expedition to set up additional instruments in the area.