1997–1998 El Niño / 1998–1999 La Niña

NASA image of 1997-1998 El Niño event.

TOPEX/Poseidon, NASA, JPL.

The 1997–1998 El Niño, the most-recent severe climate oscillation, fueled the formation of 18 tropical systems in the South Pacific, but only Susan and Ron reached the category 4 or 5 levels (Hoarau et al. 2008). Wind-driven waves and abnormally high sea levels contributed to hundreds of millions of dollars in flood and storm damage in the San Francisco Bay region, including Point Reyes National Seashore, Golden Gate National Recreation Area, and Pinnacles National Monument.

Marin Headlands, Golden Gate Bridge, San Francisco Bay and City. Golden Gate National Recreation Area, California.

NPS photo.

Scientists at the U.S. Geological Survey analyzed nearly 100 years of sea-level records at Fort Point, near the Golden Gate Bridge in Golden Gate National Recreation Area, and found that these abnormally high sea levels were the direct result of the 1997–1998 El Niño (Ryan et al. 1999). At one time during the El Niño winter of 1998, 95% of the trails in Point Reyes National Seashore were closed due to downed trees, erosion, unstable cliffs, mudslides, or wash outs. Some trails remained closed for more than a year.

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

NPS photo.

In addition to California, the 1997–1998 El Niño and the following 1998–1999 La Niña severely impacted the Pacific Northwest, including many National Park System units: 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. Typically, the Pacific Northwest has mild winters as a result of El Niño’s warm ocean currents, but six major storms occurred between 1997 and 2000 offshore from the Pacific Northwest, each generating waves that exceeded 33 feet (10 m) (Allan and Komar 2002). The strength of these storms and corresponding high-water levels caused substantial coastal erosion.

Winter storm in Pacific Northwest, 1999

NOAA, NESDIS, OSEI image.

The occurrence of such an extreme storm was unexpected because during an El Niño the storm systems tend to cross the West Coast farther to the south in central to southern California, rather than passing directly over the Pacific Northwest. The severe wave conditions were far worse during the following 1998–1999 La Niña winter, when 17 to 22 major storms occurred off the coast. The largest storm developed on 2–4 March 1999, generating a 46-foot (14.1-m) wave. Hence, as stated by Allan and Komar (2002), “the Pacific Northwest received a ‘one-two punch’ from the successive El Niño and La Niña winters.”

NASA image of pacific coast of the U.S.

NASA, Jacques Descloitres.

Related Links

• NPS—Coastal Geology
• NPS—Coastal Geohazards
• NPS—Geology
• NPS—Oceans