| Abstract |
On January 5, 1991, at 2230 h local time, a catastrophic landslide occurred in the Zunil I geothermal field, in western Guatemala. The area is characterized by high relief, steep terrain, and is located on the flanks of Cerro Quemado Volcano. Active faults permeate the geothermal field, which is well known for its abundant fumaroles and hydrothermally altered volcanic rocks. The slide engulfed an area known locally as "la calera", ("lime-like") that contained active fumaroles as well as the access road and drill pad for well ZCQ-4. Prior to that, la calera was the site of small scale prospection for mercury. The landslide is multi lobate in shape and is nearly 800 m long; is varies from 200 to 300 m in width. Accurate measurements of thickness are difficult to obtain, but estimates vary from there to ten meters. Twenty three people were killed in this landslide. Initial reports by the Associated Press (AP) attributed the slide to an exploration at geothermal well ZCQ-4, which was heavily damaged and buried by the slide. Subsequent reports erroneously stated that an explosion occurred at an unfinished geothermal power plant and compared the blast and tragedy to the 1986 disaster at the Chernobyl nuclear power plant. Press reports in Guatemala were particularly inflammatory and harshly critical of the developers. Statements issued by the Guatemalan government agency responsible for the Zunil I project (INDE) and spokesman for the geothermal industry refuted early press reports and blamed the cause of the landslide on natural causes. This paper describes an investigation of the landslide that was conducted in Guatemala between January 21, and January 26, 1991. The observations and conclusions represent a team effort and include descriptions of the site geology, engineering geology, and well head assembly. Underlying factors that may have contributed to slope instability are identified and several components that may have triggered the slide are discussed. Recommendations for the Zunil field and similar geothermal areas are provided. |