Map showing Landslide Susceptibility in the Comerío Municipality, Puerto Rico

By Matthew C. Larsen and John E. Parks

In cooperation with the
MUNICIPIO COMERÍO, PUERTO RICO

Open-File Report 98-566

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ABSTRACT

In Puerto Rico, the combination of mountainous terrain and frequent intense rainstorms results in a landscape where landslide features are commonplace. The risk of landslides occurring during intense or prolonged rainfall is high in steeply-sloping interior municipalities such as Comerío, where 77 percent of the 74-square-kilometer municipality has slopes of 21 percent (12°) or more. A set of simplified matrices representing geographic conditions was developed from earlier studies in three other regions of the central mountains of Puerto Rico and provides a basis for the estimation of the spatial controls on the frequency of rainfall-triggered landslides. Four geographic characteristics were used to categorize hillslope types: elevation, slope, aspect, and land use. The frequency of landslides is higher in the wetter regions of the island, or generally at elevations greater than 300 meters. In general, hillslopes with a slope angle of 12 percent (7°) or less have a relatively low landslide frequency. A slope angle in excess of 21 percent (12°) is a threshold above which the frequency of landslides is relatively high. In Puerto Rico, slope aspect is also relevant because hillslopes that generally face the prevailing winds, which deliver much of the rainfall to the island, have the highest frequency of landslides. Conversely, hillslopes facing away from the prevailing winds have the lowest frequency of landslides in the study areas. Hillslopes in the remaining quadrants generally have an intermediate landslide frequency. The greatest variation in the frequency of landslides exists among land use categories. A map showing landslide susceptibility in the Comerío municipality was developed by dividing the municipality into generalized regions of low, moderate, and high landslide susceptibility. These susceptibility zones were amended by including additional areas defined by the locations of ancient landslide deposits taken from geologic maps and recent and historic debris-flow tracks and runout zones.

TABLE OF CONTENTS

Abstract
Introduction
Methods

Results

Conclusion

Acknowledgments

References

The citation for this report, in USGS format, is as follows:

Larsen M.C. Map Showing Landslides Susceptibility in the Comerío Municipality, Puerto Rico, 1 plate.

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