This lake is a natural lab.

This lake is a natural lab

It's rare event when Lake Eyre South in Australia is inundated with a major flood; the lake's water usually escapes through one of the continent's largest inland drainage systems. So when J.A.T. Bye of the Flinders University of South Australia in Bedford Park and his colleagues went to study the lake in March 1984, two months after it experienced major flooding, it was a special scientific opportunity to learn more about the lake. Indeed, Bye's group was treated to a wonderful discovery: The lake acted as a huge natural laboratory for studying the flow of fluids. The swirling pattern near the island shown in this aerial view of the lake is one of several different kinds of fluid structures observed by the researchers.

Bye and his colleagues think the visibility of the fluid patterns springs from the two different kinds of solutions created in the lake as it floods. In some regions the salt crust of the lake bed is dissolved to form a saline solution, while in others a fine silt is stirred up. The two solutions don't mix very well, possibly because the silt clumps up in the salt water, and so the boundary between them remains fairly distinct. This enabled the researchers to see a variety of fluid phenomena as wind-induced currents pushed one kind of fluid into another over different kinds of lake bed surfaces.

The researchers note that, in experiments conducted on much smaller scales, they and others have been able to reproduce the major types of mixing patterns in the lake with remarkable fidelity.

When the researchers returned to the lake in July 1984, none of the striking flow structures were apparent, probably because the silt had settled and the salt crust had completely dissolved. Now Lake Eyre South is a dry salt marsh again, the reserchers write in the Feb. 4 EOS. "Nature has closed the theater," they say, "and it may be some years before there is another performance."