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REPORT:
Volcano Hazards at Fuego and Acatenango, Guatemala


-- J.W. Vallance, S.P. Schilling, O. Matías, W.I. Rose, and M.M. Howell, 2001,
Volcano Hazards at Fuego and Acatenango, Guatemala U.S. Geological Survey Open-File Report 01-431

Introduction

The Fuego-Acatenango massif comprises a string of five or more volcanic vents along a north-south trend that is perpendicular to that of the Central American arc in Guatemala. From north to south known centers of volcanism are Ancient Acatenango, Yepocapa, Pico Mayor de Acatenango, Meseta, and Fuego. Volcanism along the trend stretches back more than 200,000 years. Although many of the centers have been active contemporaneously, there is a general sequence of younger volcanism, from north to south along the trend.

This massive volcano complex towers more than 3,500 meters above the Pacific coastal plain to the south and 2,000 meters above the Guatemalan Highlands to the north. The volcano complex comprises remnants of multiple eruptive centers, which periodically have collapsed to form huge debris avalanches. The largest of these avalanches extended more than 50 kilometers from its source and covered more than 300 square kilometers. The volcano has potential to produce huge debris avalanches that could inundate large areas of the Pacific coastal plain. In areas around the volcanoes and downslope toward the coastal plain,more than 100,000 people are potentially at risk from these and other flowage phenomena.

In historical time, Fuego has erupted more than 60 times. It has spread volcanic ash to population centers such as Escuintla (population 75,000+) 20 kilometers to the south, Antiqua (population 25,000) 15 kilometers to the southwest and Guatemala City (population 2.2 million), the country's capital and largest city, 40 kilometers to the southwest. The volcano commonly produces plumes of fine ash up to 10 kilometers high, lava flows, and hot pyroclastic flows. During periods of rain, volcaniclastic debris remobilizes to form volcanic debris flows (also commonly known as lahars). After periods of volcanism, channels are choked with sediment. As a result, floods spill onto adjacent interfluves, and periodically river channels change their course.

The only known historical eruptions of Acatenango volcano occurred in the 20th century, between 1924 and 1927 from just north of the summit peak (Pico Mayor) and again in December 1972 from the saddle between Yepocapa and Pico Mayor. These phreatic explosions generated ballistic bombs that fell near the summit craters and fine ash that fell up to 25 kilometers away. In prehistoric time, Acatenango has erupted explosively to form widespread fall deposits, hot pyroclastic flows and lava flows. There have been numerous eruptions during the past 80,000 years from vents along the massif. The most recent explosive eruptions of Acatenango occurred 1,900 years ago (Pico Mayor), 2,300 years ago (Pico Mayor) and about 5000 years ago (Yepocapa). If such eruptions were to recur, many people and costly infrastructure would be at risk.

Volcanic eruptions are not the only events that present a risk to local communities. Another concern is a small-to moderate-sized landslides that could occur during periods of no volcanic activity. Landslides could be triggered on Acatenango and Fuego volcanoes by torrential rainstorms and earthquakes, and as they move down slope such landslides can transform into lahars that can inundate downstream areas beyond the edifice. Fuego demonstrates a more likely scenario in which torrential rains trigger debris flows by mobilizing fresh pyroclastic debris in the steep barrancas of the edifice. The rain-induced lahars that occurred after the modest eruptions of 1999 at Fuego show the destructive power of even small events. These debris flows destroyed newly constructed highway bridges in at least two places east of the volcano.

This report describes the kinds of hazardous events that occur at volcanoes in general and the kinds of hazardous geologic events that have occurred at Acatenango and Fuego in the past. The report also shows, in the accompanying volcano-hazards-zonation maps, which areas are likely to be at risk when hazardous events occur again.


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02/12/02, Lyn Topinka