Inventory of landslides triggered by hurricane Matthew in Guantánamo, Cuba


 An inventory of landslides triggered by Hurricane Matthew (4–5 October 2016) through the eastern region of Cuba was carried out using Sentinel 2A satellite images. The inventory was compared with the slope map generated from the digital elevation model at 25 m per pixel and with the geological map at 1: 100 000 scale. The precipitation data from the 1-hour rain gauge records of four stations of the Cuban Institute of Meteorology (INSMET) and 24-hour rain gauge records of six stations of National Institute of Hydraulic Resources (INRH) were processed and analysed during this event. In total, 237 landslides were classified into rockslides, debrisflows and topples. A wide distribution of landslides was found within the selected slope classes, depending of the landslide type. Most of the landslides were generated in green schist of volcanic and vulcanoclastic rocks and rocks of the ophiolitic complex made up of ancient remains of oceanic crust. Findings increase understanding of landslide occurrence in this area in order to update landslide hazard map and to reduce landslide risk.


Introduction
Landslide inventory databases are becoming available to more countries and several are now also available through the internet. A comprehensive landslide inventory is a must in order to be able to quantify both landslide hazard and risk . A signi cant part of the methodologies for landslide risk assessment include as a fundamental input, detailed information on the previous occurrence of landslides in the study area (Dai et al. 2001;Ayalew and Yamagishi 2005). There have been research on landslide inventory worldwide (Brown et al. 1992), as well as nation or regional ones (Guzzetti et al. 1994;Marcelino et al. 2009).
The island of Cuba is the largest of the Caribbean region with 109 884 km 2 (ONEI 2020). Its eastern area is the most prone to the occurrence of landslides, due to the abundance of mountainous areas with steep slopes (Castellanos and Van Westen 2007). In Cuba, most of landslides are associated to meteorological events such as hurricanes, tropical storms or prolonged periods of rain . The eastern region of Cuba is frequently exposed to those meteorological phenomena due to the geographical location of the archipelago in a very active hurricane zone, according to the Chronology Report of Tropical Cyclones in Guantánamo for period 1851-2019, produced by the Guantánamo Meteorological Center. The landslide hazard, vulnerability and risk assessment carried out in Guantánamo province as part of the national effort to improve disaster management, also concluded that rainfall is the most important triggering factor for these events in the area (Savón et al. 2016).
The landslide inventory currently available for the eastern zone was carried out by photointerpretation of aerial photos from 1956 at 1:62 000 scale and 1974 at 1:37 000 scale Castellanos 2000). After these inventories, there was not an update with the occurrence of more recent signi cant meteorological events.
The year 2016 was a very active from the meteorological point of view for the easternmost region of Cuba due to the occurrence of events that caused heavy rainfall. In the study area there were 19 events recorded by stations of the Institute of Meteorology and the Institute of Hydraulic Resources. For a 24-hour accumulated rainfall regime, two months recorded the most heavy rain events: April with ve events and accumulated rainfall of 863.3 mm; and October with 12 events of heavy rainfall and accumulated 2448.6 mm. Among these events, Hurricane Matthew stands out for its regional impact, which caused signi cant damage in different Caribbean islands and in the United States of America with winds corresponding to a category 3-5 hurricane on the Sa r-Simpson scale, intense rains, and coastal ooding (Ballester and Rubiera 2016;Steward 2017).
In the present work, after characterizing the rainfall of Hurricane Matthew, we presents the inventory of landslides triggered by this event as it passes through the eastern part of Cuba. The rainfall was analyzed by using rain gauge data collected by the Institute of Meteorology (INSMET) and the National Institute of Hydraulic Resources (INRH).

Study area
The area of in uence of Hurricane Matthew was the eastern corner of the island of Cuba (Figure 1). Low mountains (less 600 m) predominate in this area with some frequently heights less than 1200 m, coastal plains and small intra-mountains valleys surrounded by steep slopes are the most common at areas.
This region is complex from the lithological and structural point of view. It is composed of the rocky complexes of the Cretaceous basement, with rocks of the metamorphic complex, mainly sericite and albite schists and andesite-basaltic lavas. The layers are nely strati ed and rocks of the ophiolitic complex have a high degree of fracturing. There are also rocks of the Paleogene volcanic island arc with predominance of tuffs. To a lesser degree, there are rocks of the Neogene-Quaternary coverage composed mainly by the alternation of sandstones, lutite, calcareous lutite and biodetritic limestones (Iturralde-Vinent 1998). The marine terraces composed of bioclastic and biogenic limestone, calcareous sandstone generated by a combination of recent movements of the earth's crust with the cycles of sea levels due to glaciations stand out in the coastal area (Castellanos 2000).
The mountain ranges in the area represent one of the most extensive and well-preserved mountainous ecosystems in the Antilles. Four distinct terrestrial ecoregions from the 193 recognised in the world are present: Cuban moist forest, Cuban dry forest, Cuban pine forest, and Cuban cactus scrub (Olson et al. 2001). Such diversity in a small extension rank the area among the top biodiversity hotspots in the Caribbean. The soils are highly diversi ed with 13 types and 18 subtypes, most of them with low crop potential mainly used for forestry.
Accordingly, there is a high concentration of fauna in this area, which is relevant for the Caribbean by its either abundance, diversity or endemism. The region is considered the oldest center of evolution of the ora of Cuba, representing one of the oristic regions with the highest endemism of the Greater Antilles, with 928 endemic species, almost 30% of those reported for Cuba, of which 366 are exclusive to the region (Borhidi 1996). There are also 22 plant formations of the 26 de ned for Cuba (Puchkov et al. 1989). It is the location of the last remnants of rainforests in Cuba, considered an important productive natural ecosystem (Lastres 1988). In summary, both ora and fauna in the study area are ecologically signi cant for the country and the Caribbean region.  The highest accumulated precipitation due to Hurricane Matthew was recorded at stations 78369, 78319 and 78334 (located in Figure 1B). The day 4 was the one with the highest precipitation in the entire area affected by the meteorological event as shown in Table 1.
The rainfall associated with the hurricane and its feeding bands were intense, speci cally on the days of Hurricane Matthew. It behaved as shown in Table 1, with considered raining on the day 4 in the station 78369 and on the day 5 in stations 78319 and 78334.   Figure 3 shows rainfall events recorded one month before and one month after hurricane Matthews arrival. It possible to see the increasing of rainfall event with Matthews, highlighting station 78319 with 11 and 19 intensive rainfalls and the station 78334 with 12 and 16 intensive rainfalls. It is also possible to note how precipitation remains higher than before, after Hurricane Matthews crossing the Guantánamo province.

Methods
An inventory of landslides was carried out for the period from August 2016 to January 2017. The main source of information for this inventory were Sentinel 2A satellite images from MSI instrument operated by the European Space Agency (ESA). Moderate resolution (10 m per pixel) true color and false color near-infrared images were generated from level 1C products. Images dates, identi er, size and cloud percentage are shown in Table 2. The limits of the area of interest were de ned taking into account the frame of topographic sheets at 1:10 000 scale. High-resolution post event satellite images provided by free internet providers Google and Microsoft where used as additional source of information. The study area was divided into 183 squares of 5 x 5 km and a visual interpretation was made using the Normalized Difference Vegetation Index (NDVI), identifying the landslides. Each cell was examined and compared with the exposure of soils, rocks and the existing vegetation in it, classifying the cells taking into account the amount of landslides by squares.
After visual interpretation, eld visits were made in the study area for the purpose of checking and direct identi cation of some landslides, as well as to con rm potential areas of occurrence of these events. Several eldwork routes were traced through the towns affected by the hurricane.
In order to understand the behavior of the rain as a triggering factor, the precipitation data from 1-hour rain gauge stations operated by INSMET and 24-hour rain gauge stations operated by INRH for October 2016 was compiled and analyzed.
Once the landslide inventory was completed, these were spatially compared with the slope map generated from the digital elevation model at 25 m per pixel. Similarly, the inventory was compared with the geological map at 1:100 000 scale (IGP 2016).

Results And Discussion
The landslide inventory carried out in the study area found 237 events that could be associated to Hurricane Matthew taking into account the freshness of the material movement and the loss of the soil layer. Landslide were classi ed into three main types: rockslides, debris ows and topples. Figure 3A shows a 5 x 5 km 2 grid with landslide numbers by cell. As can be seen, there were areas with high occurrence of landslides that reached up to 34 counts. The vast majority were shallow landslides as shown in Figure 3B.
Regarding the relationship between the occurrence of landslides and rainfall, we found that according to the spatial location and the radius of in uence of the rain gauges, most of the landslides were concentrated in the areas with the precipitation recorded by of station 78334 (see table 1 and gure 3). This nding con rms the relationship of the occurrence of landslides with events of intense rainfall found by other authors (Lumb 1975;Garland and Oliver 1993;Kay and Chen 1995;Finlay et al. 1997;Crosta 1998Crosta , 2003Guzzetti 1998;Crozier 1999;Dai et al. 2001;Aleotti 2004;Dikshit et al. 2019;Sarkar and Dorji 2019). Station 78334 also registered intensive rains, but it is located in an area of an intra-mountain valley, which is why not many landslides occurred in that area.
Slope angle is very important as part of the conditioning factors generating landslides as mentioned by Aristazabal and Gómez (2007) and Aristizábal and Yokota (2006). Figure 5, shows the relationship of the slope classes and elevation of the landslides in the study area. It is notable that rockslides have a wide distribution in the nine established slope angles classes, diminishing towards the 35-40° and >45°c lasses. Only four rockslides were found in areas with more than 45° slope angle. With respect to elevations, rockslides have their greatest distribution within the range of 100-600 m with 132 events.
In the case of topples, their distribution was limited to slopes of classes 10-15 and 15-20 with heights between 30-45 meters above sea level. These occurred in the marine terrace system as mentioned by Castellanos (2000). For the debris ows they present their distribution within the slope classes <10°, 10-15° and 30-35°. However, in terms of elevation they are framed within 170-450 m.
Most of the rockslide-type landslides are generated in materials represented by green schists of volcanic and vulcanoclastic rocks and rocks of the ophiolitic complex constituted by ancient remains of oceanic crust and within its composition we nd harzburguites, lherzolites and serpentinized dunites of the Cretaceous Lower-Upper and Middle Jurassic as shown in Table 2. These are the oldest rocks in the study area and present different degrees of weathering and high deformation.
Debris ows only occurred in rocks from the Middle Jurassic ophiolitic complex and in magmatic rocks and to a lesser degree in rocks composed of green schists of volcanic and vulcanoclastic rocks of Cretaceous age; Topples only developed in the Maya formation composed of organodetritic and organogenic limestones from the Upper Pliocene-Upper Pleistocene.

Conclusions
Hurricane Mathew affected Guantánamo province in Eastern Cuba triggering 237 landslides as interpreted by satellite images. The majority of the landslides found were rockslides with a small amount of debris ows and topples. The areas with higher rainfall coincides with highest landslides occurrence, except for intra mountain valleys, which is in accordance with the nature of the event.