Vol. 8, No. 8 August 1998 INSIDE • Penrose Conferences, p. 7, 19 GSA TODAY • 1998 Medals and Awards, p. 8 • New Members Fellows, and A Publication of the Geological Society of America Student Associates, p. 20, 21 Slope Failure and Shoreline Retreat During Northern California’s Latest El Niño El Niño Response Group* S. H. Cannon, S. D. Ellen, S. E. Graham, R. W. Graymer, M. A. Hampton, J. W. Hillhouse, D. G. Howell, A. S. Jayko, R. L. LaHusen, K. R. Lajoie, R. J. Pike (lead compiler/editor), D. W. Ramsey, M. E. Reid, B. M. Richmond, W. Z. Savage, C. M. Wentworth, and R. C. Wilson U.S. Geological Survey ABSTRACT Surface processes accelerated by severe storms during the 1997–1998 El Niño event scoured hillsides and damaged property across coastal Cali- fornia. Technological advances such as digital mapping, exemplified here for the San Francisco Bay area but applicable elsewhere, have enabled government agencies to better describe, monitor, and predict the effects of shoreline erosion and slope failure. INTRODUCTION Major storms struck California in 1997–1998, ravaging the coast and spawn- ing floods and landslides (Fig. 1). By late spring, property losses statewide had exceeded $550 million, and 35 counties were declared Federal Disaster Areas. Mindful of severe winters past (Ellen, 1988) and the predicted El Niño anomaly, the U.S. Geological Survey (USGS) joined other agencies to anticipate new areas of hazard while sustaining monitoring efforts already in place across the state (http:// www.usgs.gov/elnino.html). Here, we illustrate some of the winter’s destructive geomorphic effects in the San Francisco Bay area (Fig. 2) and describe attempts to forecast them at a regional scale. Figure 1. Existing landslides—slumps, slides, and earthflows (red) for part of San Francisco Bay area, Our efforts targeted shoreline erosion on shaded-relief base (Wentworth et al., 1997). Photo: Reactivated 100-acre earthflow on Mission Peak, Fremont, and threatened homes (see Fig. 2 for location). In late March 1998, slide was still moving and slope failure. Permanent loss of 1 m/day. Photo by J. D. Rogers. coastal land and the structures on it to winter storms is an ongoing problem in northern California. Large waves coincide with the seasonally high tides (and in expansion) to erode beaches and undercut meters and involving surficial mantle and El Niño years, a sea level raised by thermal sea cliffs already weakened by saturated bedrock 1 to 50 m thick (Fig. 1), can per- soil. Two types of landslides are common sist for thousands of years (Varnes, 1978). in the Bay area. Debris flows are slurries Coastal California’s Mediterranean *Addresses (all USGS): Cannon and Savage— that run rapidly downslope and form thin, climate contributes to these damaging P.O. Box 25046, Lakewood, CO 80225; LaHusen— ephemeral deposits; the slower-moving processes (Fig. 3). Normal Bay area pre- 5400 MacArthur Blvd., Vancouver, WA 98661; all others—345 Middlefield Road, Menlo Park, slumps, translational slides and earth- CA 94025. flows, covering up to several square kilo- El Niño continued on p. 2 IN THIS ISSUE GSA TODAY August Vol. 8, No. 8 1998 Slope Failure and Shoreline Retreat GeoPals Program ...................... 15 During Northern California’s GSAF Update .......................... 16 GSA TODAY (ISSN 1052-5173) is published monthly Latest El Niño ........................ 1 by The Geological Society of America, Inc., with offices at 3300 New Members ......................... 20 Penrose Place, Boulder, Colorado. Mailing address: P.O. 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Written permission is required from GSA for all other forms of capture, reproduction, and/or distribution of any Daniel I. Axelrod Philip Oxley Stuart L. Schoff item in this publication by any means, including posting on Davis, California Washington, D.C. Maryville, Tennessee authors’ or organizational Web sites, except that permission is granted to authors to post the abstracts only of their sci- June 2, 1998 June 19, 1998 June 28, 1998 ence articles on their own or their organization’s Web site providing the posting includes this reference: “The full paper Ruth B. Curtis Hans Ramberg Ward C. Smith was published in the Geological Society of America’s news- Boulder, Colorado Uppsala, Sweden Cupertino, California magazine, GSA Today, [include year, month, and page num- June 5, 1998 May 5, 1998 June 25, 1998 ber if known, where article appears or will appear].” GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or polit- ical viewpoint. Opinions presented in this publication do not reflect official positions of the Society. El Niño continued from p. 1 mid-April), providing waterlogged ground conducive to landsliding, slumping of SUBSCRIPTIONS for 1998 calendar year: Society Members: GSA Today is provided as part of membership cipitation peaks in mid-winter at 15 cm coastal bluffs, and flooding during winter dues. Contact Membership Services at (800) 472-1988, (6 in.)/mo, while evapotranspiration rainstorms. 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Lehr Bay region covered by Managing Editor: Faith Rogers Assistant Editor: Vanessa Carney new digital maps of Production Manager: Jon Olsen existing landslides, Production Editor and Coordinator: Joan E. Manly debris-flow sources, Graphics Production: Joan E. Manly, Leatha L. Flowers shaded relief, slope angle, and rainfall ADVERTISING: Classifieds and display: contact Ann Crawford, (303) 447-2020; fax 303-447-1133; acrawfor@ thresholds. Numbers geosociety.org. show locations of Fig- ures 1 (photo), 5–7, Issues of this publication are available as electronic Acrobat files for free download from GSA’s Web Site, http://www.