The Islands' soils are so saturated with water after last week's rains that another storm predicted for this week could increase the chance of landslides and damaging flooding, geologists say.

Residents near steep, soaked hillsides should watch for signs of movement — things such as cracks in the soil, humps in the soil or light rockslides that could be precursors to further movement.

"If there is any unusual geological activity, they should call in a geologist or soils engineer," said University of Hawai'i geology professor Steve Martel. "When it rains, there's an elevated potential of rockfalls and landslides."

The risk doesn't end when the rain stops. There is frequently a time lag, he said.

Fellow geology professor John Sinton said soils on steep slopes become unstable because the water makes them heavy, and it provides lubrication. If the ground then dries out slightly and is drenched again, it can become even more unstable, he said.

"If the ground is already heavy and lubricated, things can slide more readily," Sinton said.

Martel said that while the risk level is high, property owners have limited options if they suspect problems.

"There are a lot of issues right now," he said. "Nobody in the state is looking at each slide risk on a daily basis."

Clifford Inn, public information officer for the state Department of Land and Natural Resources, confirmed the state geologist's position is vacant due to a retirement and the deputy geologist is on leave.

The rains have saturated the soils, leaving them prone for flooding with the next rain, since they have no capacity to soak up further moisture.

"Everybody is being very cautious. The ground is pretty saturated, and it wouldn't take as much rain to cause a flood," said Rick Fontaine, a hydrologist with the U.S. Geological Survey. He said that both Lake Wilson and Kawainui Marsh reached flood levels that prompted preliminary alerts during the worst of last week's storm, but that water levels were dropping by Friday.

Fontaine said that a stream gauge in Kahana Stream on the Windward side had flow levels comparable to a five-year flood — the amount of water flow that would be expected no more often than once in five years. Again, it was dropping during the day Friday, he said.

University of Hawai'i coastal geologist Charles Fletcher said that muddy runoff during heavy rain is a normal feature of Island geology, and coastal systems such as reefs are able to survive the results of an occasional mud influx. But he said that the presence of fallow agricultural fields could increase the sediment load beyond what the natural system is accustomed to.

"We need to be concerned that these discharges could be greater than normal," he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.