Island ground water reacts to big surf

Deep under the islands' surfaces, the groundwater is moving.It flows, of course, from the mountains toward the sea. As rain falls on the surface of islands, it percolates down and forms a vast underground lake within the volcanic matrix. That lake is constantly at flow seaward, where the island's fresh water leaks into the salt water surrounding the islands.When storm surf occurs, it shoves vast amounts of water up against the island, creating a rise in the overall level of the water.

In some areas, swimmers can feel its cool flow where it enters the ocean below the surface near shore.But the groundwater also moves up and down.Researchers have long known that the water in the islands' aquifers rises and falls with changes in atmospheric pressure. But it also moves with the tides, and with periods of storm surf along the coast.When storm surf pounds an island's shore, the change in the height of the groundwater can be measured in wells miles inland, according to research by Kolja Rotzoll, of the U.S.

Geological Survey's Pacific Islands Water Science Center.Rotzoll and Aly El-Kadi, both associated with the University of Hawai'i UH Dept of Geology andGeophysics Water Resources Research Center, published their study on the subject in the Journal of Hydrology. The work was part of Rotzoll's work toward his doctorate degree. Its aim was to better understand the movement of water in the aquifers under islands.

In research on Maui, he found that the impact of a major storm surf event on the coast can be measured as a rise in the water level in wells more than three miles in from the shore.
“The change in water level travels through the aquifer and can be detected as a net rise in the ground-water table kilometers away from the coast,” he said in an email.The effect is apparently the reaction to a rise in sea level at the coast.