22–25 Sept. GSA 2019 Annual Meeting & Exposition VOL. 29, NO. 6 | JUNE 2019 Landslides Triggered by Hurricane Maria: Assessment of an Extreme Event in Puerto Rico FUS_125 Creative Ad Concepts_MECH_OL.pdf 1 5/1/19 8:54 AM JUNE 2019 | VOLUME 29, NUMBER 6 SCIENCE 4 Landslides Triggered by Hurricane Maria: Assessment of an Extreme Event in Puerto Rico GSA TODAY (ISSN 1052-5173 USPS 0456-530) prints news Erin Bessette-Kirton et al. and information for more than 22,000 GSA member readers and subscribing libraries, with 11 monthly issues (March- Cover: Landslides triggered by Hurricane Maria in Sept. 2017 in the April is a combined issue). GSA TODAY is published by The municipality of Utuado, Puerto Rico. Photo taken by Erin Bessette- Geological Society of America® Inc. (GSA) with offices at 3300 Penrose Place, Boulder, Colorado, USA, and a mail- Kirton during helicopter reconnaissance on 29 Oct. 2017. See related ing address of P.O. Box 9140, Boulder, CO 80301-9140, USA. article, p. 4–10. 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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 km2 (Fig. 1A). 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 GSA Today, v. 29, https://doi.org/10.1130/GSATG383A.1. Copyright 2019, The Geological Society of America. CC-BY-NC. 4 GSA Today | June 2019 A B Figure 1.