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Pacific Coastal and Marine Science Center

Natural Oil & Gas Seeps in California

The Effects of Seeps on the Environment

Unlike man-made pollutants, most oil and gas seeps are produced by natural geologic processes that take place over millions of years. Though natural, they can pollute our air and waterways.

By knowing where natural oil and gas seeps occur, we can distinguish their effects on the environment from the effects of man-made oil and gas leaks and spills.

Some examples of potential environmental problems resulting from oil and gas seeps are shown in these photographs.

Photo of cliff-side oil seep; see caption.This natural oil seep, at the base of a sea cliff near Santa Barbara, covers the beach sand with an impressive build-up of black asphaltum. This tar-like substance is eroded by waves to form pesky tar-balls, which are carried by longshore currents to other beaches, miles away.

Photo of gas seep; see caption.Naturally occurring gas seeps, such as this one in Humboldt County, contain methane, a greenhouse gas that contributes to global warming.

Photo of oil seep; see caption.Natural oil seeps like this one, at Tar Water Creek in the Santa Cruz Mountains, can degrade water quality and endanger wildlife.

Photo of a chunk of mercury ore.Oil is a common companion of mercury, the most toxic of natural metals.

This chunk of mercury ore, from the abandoned New Almaden mercury mine near San Jose, California, has oil hiding inside tiny vugs and in the area stained brown on the righthand side of the specimen. Geologists think hot fluids carried the mercury and oil from deep underground.


California Oil and Gas Seeps Home

The “Natural Oil and Gas Seeps in California” project is a collaborative between the USGS and the California Department of Conservation

See also:

Pacific Coastal and Marine Science Center

USGS Coastal and Marine Geology Program

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Page Last Modified: 19 January 2011 (lzt)