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Figure 1. (A) Topographic map of Puerto Rico showing the storm track of Hurricane Maria. (B) Relative density of landslides mapped from
the rapid classification of satellite and aerial imagery and site visits following Hurricane Maria (updated from Bessette-Kirton et al., 2017).

1340 m (U.S. Geological Survey, 2017c; complex is unconformably overlain by a maximum rainfall values range from
Fig. 1A). Broad lowlands and coastal cover sequence of Oligocene–Pliocene 353 to 1431 mm (see [A] in the GSA Data
plains ring most of the island. Present- carbonates and associated siliciclastic Repository for a summary of rainfall
1
day tectonic uplift resulting from the deposits (Monroe, 1976; Ortega-Ariza data). Doppler estimates are not available
convergence of the North American et al., 2015). due to the destruction of radar during
and Caribbean plates is one of the main the storm (National Weather Service,
drivers of the rugged topography that is HURRICANE MARIA 2017b). Although rainfall estimates from
expressed across much of the island Hurricane Maria made landfall along Hurricane Maria vary, multiple data sets
(Taggart and Joyce, 1991; Brocard et al., the southeast coast of Puerto Rico as a indicate that at least 250 mm of rain fell
2015, 2016). The average annual rainfall Category 4 hurricane at 6:15 a.m. local across Puerto Rico’s mountainous terrain,
varies dramatically across micro-climate time (Atlantic Standard Time [AST]) on much of which had received 254–381 mm
zones, with the highest annual rainfall 20 September 2017 (Pasch et al., 2018) of rainfall from Hurricane Irma two weeks
usually reported around the Sierra de and moved across Puerto Rico with a prior to Maria (5–7 September 2017;
Luquillo (Fig. 1A) in the northeastern part west-northwest trajectory (Fig. 1A). Cangialosi et al., 2018).
of the island (Ravalo et al., 1986; Daly et Rainfall data from Hurricane Maria vary
al., 2003). High rainfall, temperature, and both in absolute magnitude and spatial LANDSLIDE DISTRIBUTION
humidity contribute to widespread sapro- distribution. Estimates of average island- AND CHARACTERISTICS
lite formation (Murphy et al., 2012). wide rainfall from the National Hurricane To rapidly assess the areas that were
Puerto Rico is part of an extinct volcanic Center (NHC; Pasch et al., 2018), the most severely impacted by landslides, we
island arc that lies along the North America– National Centers for Environmental used post-hurricane satellite (DigitalGlobe
Caribbean plate boundary and is underlain Prediction (NCEP; National Weather Inc.) and aerial imagery (Sanborn and
by a faulted basement assemblage of Upper Service, 2018), and the PERSIANN-Cloud Quantum Spatial; Vexcel Imaging, 2017)
Jurassic ocean crustal fragments and Classification System (CCS; Center for collected between 26 September and
Cretaceous to Eocene volcaniclastic and Hydrometeorology and Remote Sensing, 8 October 2017 to map landslide density.
intrusive units (Jolly et al., 1998). This arc 2018) range from 280 to 543 mm, while A few of the landslides that we mapped

1 GSA Data Repository item 2019079, (A) summaries of published rainfall and soil moisture data from Hurricane Maria and (B) database of past hurricanes and
tropical storms in Puerto Rico with landslide occurrences described when applicable, is available online at www.geosociety.org/datarepository/2019.

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