1997-1999: El Niño sea surges in California, then La Niña storms in the Northwest

The 1997-1998 El Niño and the 1998-1999 La Niña that followed battered the Pacific coast from California to Washington, including a string of national park units. A National Park Service article in its "Storms of Record" coastal geology series describes what happened.

NASA image of the 1997-1998 El Niño event. TOPEX/Poseidon, NASA, JPL.

California

The 1997-1998 El Niño fueled the formation of 18 tropical systems in the South Pacific, but only two, Susan and Ron, reached category 4 or 5. In the San Francisco Bay region, wind-driven waves and abnormally high sea levels contributed to hundreds of millions of dollars in flood and storm damage, including at Point Reyes National Seashore, Golden Gate National Recreation Area and Pinnacles National Monument.

Marin Headlands, Golden Gate Bridge, San Francisco Bay and city, in Golden Gate National Recreation Area. NPS photo.

U.S. Geological Survey scientists analyzed nearly 100 years of sea-level records at Fort Point, near the Golden Gate Bridge, and found the abnormally high sea levels were a direct result of the El Niño. In the winter of 1998, at one point, 95 percent of the trails at Point Reyes National Seashore were closed because of downed trees, erosion, unstable cliffs, mudslides or washouts. Some stayed closed for more than a year.

Storm waves hit the coast at Point Reyes National Seashore, California. NPS photo.

The Pacific Northwest

The two winters also hit the Pacific Northwest hard, including Mount Rainier, North Cascades and Olympic National Parks, Ebey's Landing National Historical Reserve, Fort Vancouver National Historic Site and San Juan Island National Historical Park in Washington, and Lewis and Clark National Historical Park in Oregon.

Normally an El Niño gives the Northwest mild winters, thanks to its warm ocean currents. Instead:

• Between 1997 and 2000, six major storms formed offshore, each generating waves above 33 feet (10 m).
• In the 1998-1999 La Niña winter, 17 to 22 major storms occurred off the coast, and the largest, on 2-4 March 1999, generated a 46-foot (14.1 m) wave.

The strength of the storms and the high water they produced caused substantial coastal erosion. A storm of such strength was unexpected, because during an El Niño storm systems tend to cross the West Coast farther south, in central to southern California, not directly over the Northwest. Wave conditions were far worse in the La Niña winter. The researchers the article cites describe the successive El Niño and La Niña winters as a double blow to the Northwest.

Winter storm in the Pacific Northwest, 1999. NOAA, NESDIS, OSEI image.

NASA image of the Pacific coast of the U.S. NASA, Jacques Descloitres.

Sources

• National Park Service, "1997-1998 El Niño / 1998-1999 La Niña" (nps.gov article in the series "Coastal Geomorphology - Storms of Record"), citing Hoarau and others (2008), Ryan and others (1999) and Allan and Komar (2002); rewritten in hubnx's own words.