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Landslides Triggered by Hurricane Maria:

Assessment of an Extreme Event in Puerto Rico

Erin K. Bessette-Kirton, U.S. Geological Survey, Denver Federal Center, Box 25046, MS 966, Denver, Colorado 80225, USA;
Corina Cerovski-Darriau, U.S. Geological Survey, 345 Middlefield Road, MS 910, Menlo Park, California 94025, USA;
William H. Schulz, Jeffrey A. Coe, Jason W. Kean, Jonathan W. Godt, Matthew A. Thomas, U.S. Geological Survey, Denver
Federal Center, Box 25046, MS 966, Denver, Colorado 80225, USA; and K. Stephen Hughes, Dept. of Geology, University of Puerto
Rico, Call Box 9000, Mayagüez, Puerto Rico 00681, USA

ABSTRACT triggered widespread landslides through- triggering storms (TCs and non-TC
Hurricane Maria hit the island of Puerto out mountainous areas. Landslides dam- systems) affect Puerto Rico annually
Rico on 20 September 2017 and triggered aged and destroyed structures and roads (Pando et al., 2005). The frequency of such
more than 40,000 landslides in at least (Puerto Rico Highway and Transportation events constitutes a hazard to ~1 million
three-fourths of Puerto Rico’s 78 munici- Authority, 2017, personal commun.; U.S. U.S. citizens that reside in the predomi-
palities. The number of landslides that Geological Survey, 2017a), in some cases nantly rural interior of the island, much of
occurred during this event was two orders isolating communities for days and weeks which is characterized by rugged moun-
of magnitude greater than those reported (e.g., Radebach, 2017; Schmidt and tainous terrain (Martinuzzi et al., 2007).
from previous hurricanes. Landslide Hernández, 2017). Slope failures caused at Puerto Rico’s vulnerability to extreme
source areas were commonly limited to least three fatalities (Hennessy-Fiske, 2017; rainfall events is sobering given projec-
surficial soils but also extended into under- Irizarry Álvarez, 2017), although Kishore tions of increasingly frequent extreme
lying saprolite and bedrock. Slope failures et al. (2018) believe that the death toll from TCs in the Atlantic Ocean Basin (Knutson
occurred before, during, and after flood- Hurricane Maria was underestimated by et al., 2010).
ing, and many transitioned into long run- more than 4000 deaths, some of which As a step toward reducing landslide risk
out debris flows. Steep slopes in hilly and could have been related to landslides. during extreme, island-wide precipitation
mountainous regions were particularly Landslides were also partly responsible events, we evaluated the extent and charac-
impacted by landslides due to antecedent for damage to the communications and teristics of Maria-induced landslides
soil moisture levels that were 11%–13% electrical power transmission infrastruc- throughout Puerto Rico. Herein, we present
higher than average and rainfall totals of at ture that left much of the island without an assessment of island-wide landslide
least 250 mm within a 48 h period. High power for more than six months. density, which we compare, in conjunction
landslide densities were especially wide- Landslides occur frequently in the with rainfall data, to TCs that have affected
spread across some geologic formations mountainous regions of Puerto Rico Puerto Rico since 1960. Additionally, we
(e.g., granodiorite of the Utuado batholith); (e.g., Monroe, 1964, 1979; DeGraff et al., discuss the conditions specific to land-
however, bedrock geology alone did not 1989; Larsen and Simon, 1993; Larsen and sliding in Puerto Rico and examine the
determine the location and distribution of Torres-Sánchez, 1998; Pando et al., 2005; impact of environmental variables (e.g.,
landslides caused by Hurricane Maria. Lepore et al., 2012). Most noteworthy was rainfall, soil moisture, and geology) on
While rainfall data collected during the 7 October 1985 Mameyes disaster, observed variations in island-wide land-
Hurricane Maria were inconsistent, which killed at least 129 people and is rec- sliding. An improved understanding of
satellite-based soil moisture data were ognized as the deadliest landslide in North causative factors specific to landslides in
correlated with the distribution of land- American history (Campbell et al., 1985; Puerto Rico is important for revised sus-
slides. In the future, the use of soil mois- Jibson, 1992). Hurricanes and tropical ceptibility analyses and risk management
ture data could enable assessments of cyclone systems (henceforth referred to in anticipation of future storms capable of
regional landslide susceptibility prior to collectively as TCs) routinely affect Puerto producing widespread landsliding.
hurricanes or extreme precipitation events. Rico (Hernández Ayala and Matyas, 2016)
and are capable of producing landslide- SETTING
INTRODUCTION triggering rainfall (e.g., Campbell et al., Puerto Rico (18° 15′ N, 66° 30′ W) is
Hurricane Maria struck Puerto Rico on 1985; Jibson, 1989; Larsen and Torres- the easternmost of the Greater Antilles
20 September 2017 as the strongest hur- Sánchez, 1992). Landslides have been and covers an area of 8750 km (Fig. 1A).
2
ricane to make landfall on the island since associated with at least 17 major disaster Two-thirds of the island is mountainous,
1928 (National Weather Service, 2017a). declarations in Puerto Rico since 1960 with the east-west–trending Cordillera
Maria produced heavy rainfall and flood- (Federal Emergency Management Agency, Central range spanning most of the island
ing across most of Puerto Rico and 2018), and, on average, 1.7 major landslide- and reaching a maximum elevation of

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