The location and geophysical context of Montserrat make it highly prone to a large range of hazards, including volcanic hazards, hurricanes, tsunamis, tropical storms, landslides, flooding and droughts mainly. Although a dependency of the UK, Montserrat is classified as a Small Island Developing State (SIDS) as it has limited resources and is very vulnerable to environmental hazards. A series of climatic and geological events have been a constraint for the development of the Island and its efforts for economic independence and autonomy (Clay et al., 1999; Mitchell, 2006; Possekel, 1999; Smith Warner International, 2003; Wilson, 2010).
The table summarizes the main hazards and disasters that have been recorded in Montserrat in the last centuries.
Page | 89 Type of hazard Date Extend of damages and casualties
Hurricane 1667
Flood 24/12/1672 Marginal damage
Earthquake 1672 Marginal damage
Hurricane 1737 Severe damage due to associated flooding
Hurricane 1740 Harvest destroyed
Hurricane 1744 Harvest destroyed
Hurricane 1766 Many deaths and injuries, hundreds of housing damage and half of Plymouth destroyed Flood 1767 Some deaths, bridges and street damage and
some houses flooded
Hurricane 1772 Harvest and houses destroyed Hurricane 1792 Minor damage to the harvest Hurricane 16/09/1816 Harvest completely destroyed
Earthquake 08/02/1843 6 deaths with complete devastation of all infrastructures
Hurricane 07/08/1899 100 deaths, 1.000 people injured, 9.000 people homeless, severe devastation all over the island
Earthquake 16/03/1985 6.6 on Richter scale, damage to houses
Hurricane 17/09/1989
Table 4.1: Timeline of the main hazards and disasters recorded in Montserrat from 1667 to 2017 (adapted from Possekel, 1999)
4.1.1.1. Montserrat, exposed to several volcanic hazards
After more than 300 years of dormancy, the Soufrière Hills volcano first erupted on the 18th July 1995. Series of eruptions the occurred between 1995 and 2010. In 2017, the volcano was still considered active but there has been no magmatic extrusion since 2010 (Stinton et al., 2016). The Soufrière Hills volcano is a typical strato-volcano of subduction zone, erupting highly viscous crystal-rich andesitic magma. This high viscosity magma has the capacity to erupt both passively as a lava dome and also to generate overpressures significant enough to generate explosions. Typically, as the magma reaches the surface, it creates a dome.
Pyroclastic density currents are generated either when this dome collapses or during explosive eruption. Such flows are composed of fragments of magma, including ash and pumice. They move at high speed, between 100 and 700km/h, following valleys typically. In Montserrat, they have been recorded at temperatures ranging from 130 to 650ºC (Calder et al., 1999).
Several pyroclastic flows were recorded in Montserrat between 1995 and 2010. In 1999, some flows were recorded to have travelled up to 6kms (Calder et al., 1999). On the 26 December 1997, a pyroclastic flow produced by the collapse of the dome and of the south-western flank of the volcano, devastated 10km², with its accompanying surge, (Calder et al., 1999). This was limited to the southern part of the Island (Figure 4.3), now identified as zone V and potentially C of the Hazard Level System (MVO, DMCA, & GoM, 2011) (Figure 4.2).
Figure 4.3: Map of Montserrat showing: submarine and subaerial (based on NASA satellite photography) pyroclastic flow distribution and debris avalanche Deposit 1 (Karstens et al., 2013)
Page | 91 These also produced ash falls between 1995 and 2010. They were produced mainly during the phases of dome building and collapse, and during the explosions themselves. They are also generated by pyroclastic flows (Horwell & Baxter, 2006). Ash is made of fine particles of volcanic rock, less than 4millimetres in diameter and is produced during phreatic eruptions, pyroclastic flows and explosions. Respirable ashes are particles of less than 10 microns in diameter (SAC, 2013). Some studies showed their toxicity for human health, with a significant risk of developing chronic and acute diseases for the most exposed populations, in particular children and outdoor workers (Horwell & Baxter, 2006). The map below (Figure 4.4) shows the thickness of ash deposited on different parts of the island during the eruption cumulated between 1995 and 1999 (Searl, Nicholl, & Baxter, 2002). In the western part of the country, up to 15cms of ash were deposited (Searl et al., 2002;
Wilson, 2010). The prevailing winds generally force ash to fall to the west and north-west of the volcano.
Figure 4.4: Map of Montserrat showing the thickness of ash deposited over the island between 1995 and 1999 (Searl et al., 2002)
In addition to pyroclastic flows and ash falls, lahars constitute a major hazard in Montserrat. The Indonesian term “lahar” describes flows composed of a mixture of loose
volcanic debris and water (Barclay, Alexander, & Susnik, 2007). They can therefore occur for months to years after an eruption as long as volcanic debris remains when heavy rainfalls occur. They encompass a range of sediment-laden flow, highly concentrated flows and dilute stream flows. They can be very hazardous and can destabilize or destroy infrastructures, or even bury them. In Montserrat, they are solely the consequence of rainfalls on loose volcanic material deposited in the Belham catchment and ash over the island. The main lahars occur in the Belham River Valley, in the western part of the volcano and continue to pose a significant hazard even if the volcanic activity has remained quiet since 2010 (Figure 4.5). By burying the Belham River Valley, the lahars make the crossing more complicated between the safe zone in the north of the valley and the south, for a long time a “Daytime Entry Zone” only. It can be hazardous for those who regularly need to cross it, including farmers, workers, the residents of Garibaldi Hill in the south of Zone B and tourists (Barclay et al, 2007).
Figure 4.5: Location of the rain gauges in the Belham Valley in Montserrat (Barclay et al., 2007)
Page | 93 4.1.1.2. Climatic hazards
Like the other Leeward Islands, Montserrat is exposed to the Trade Winds, which flow mainly from the east to south-east, creating a predominant wind direction. Intense storms may generate storm surge and then severe flooding of coastal areas. The north-western part of Montserrat is the most vulnerable to those winds. Yellow Hole, to the north-east of Montserrat, Isles Bay to the west and to a lesser extent Little Bay and Carr’s Bay, to the north-west, are particularly vulnerable to storm surges (Smith Warner International, 2003). In addition to these events, hurricanes often affect the island sometimes with very serious damage. In the recorded history, 41 hurricanes have been noted, with eighteen “great storms” that caused major damage and deaths. In 1899, the whole island was devastated, with about a hundred people killed, 1000 people injured and 9000 people homeless. The last major hurricane, Hugo, occurred in 1989.
It was one of the strongest hurricanes that occurred in the Caribbean during the 20th century.
90% of houses were destroyed, eleven people killed, 40 injured and more than 3,000 were left homeless. Later, several hurricanes, like Luis and Marilyn in August and September 1995, occurred while the volcano was erupting. They did not cause major damage however, except for the destruction of the tents erected for the evacuated Montserratians (Possekel, 1999).
Other climatic hazards besides hurricanes are less well documented but regularly affect the island, inducing minor damage but creating regular costs. Some of them, like hurricanes, flooding and drought, are directly linked to extreme weather events and therefore susceptible to increase with climate change (Caribbean Development Bank, 2012; Food and Agriculture Organization of the United Nations, 2016). A change in rainfall seasonality is expected as a consequence of climate change (Caribbean Development Bank, 2012). Heavy rainfalls can lead to various risks of disaster, including flooding and landslides. Inland flooding occurs mainly in the flat areas, especially the coastal reclamations or natural ponds, in times of heavy rain. They may be enhanced by natural or artificial drains such as natural embankments or roads (Smith Warner International, 2003). The risk remains limited, however, due to the mountainous topography of the Island. Landslides correspond to gravitational movements of rocks or soil down slopes. They are either natural, mostly generated by heavy rain, or as a consequence of deforestation or construction of roads in particular. Even though Montserrat is very prone to landslides due to its physical characteristics, no major damage due to landslides was recorded (Smith Warner International, 2003). However, the increasing number of
constructions on steep slopes due to the limited availability of land reinforces the risk of damage due to landslides. Parts of the population also express a concern for the vulnerability of the inhabitants living on such slopes, especially when they are immigrants, and therefore do not necessarily have the adequate knowledge and awareness of the risk of landslide.
Extreme weather events can also be responsible for the generation of droughts in the Caribbean, and hence dramatically affect agriculture. Climate change is a major concern for the whole Caribbean region. The IPCC in its Fourth Assessment Report projects that there is a 90% chance that temperatures will increase up to 2 to 2.5ºC in the Caribbean region and a decrease of annual precipitation of 5 to 15%, particularly marked during the dry season from June to August (Food and Agriculture Organization of the United Nations, 2016). Recent major droughts have been recorded in the Caribbean, especially in years with El Nino events, in 1957, 1968, 1976-77, 1986-1987, 1991, 1994, 1997-1998, and 2009-2010 (Food and Agriculture Organization of the United Nations, 2016). In 2015, Montserrat also reported having suffered from an important drought. Although the availability of drinkable water is not seen as a concern for Montserrat, droughts may strongly affect agriculture either in Montserrat itself or in the neighbouring Islands that are in charge of providing food to Montserrat.
4.1.1.3. Geological hazards
The location of the Caribbean region on a subduction zone also leads to risk of geological hazards. The whole Caribbean region recorded frequent earthquakes during the last century, with events during the 1890s, 1930s and 1960s. Most events were minor and did not cause any damage. However, in 1843 in Montserrat, six deaths and much damage was recorded and in 1985, some houses were damaged by a 6.6 earthquake. Most of the recorded earthquakes have been assimilated to failed eruptions (Smith Warner International, 2003; Wilson, 2010).
Even if there were no major tsunamis recorded in Montserrat, it has been assessed that the risk is also present (GoM, 2011b). Tsunamis are generally due to tectonic displacements, landslides or underwater explosions. Montserrat experienced two minor tsunamis, in 1867 and in 1997. The latter was due to the collapse of a flank of a volcano, during the so called “Boxing Day collapse”, but did not cause major damage. However, the risk remains limited as only few infrastructures and dwellings are located on coastal areas. After the relocation of the population into the north of the Island, only Little Bay is assessed as exposed to the risk of tsunami (GoM,
Page | 95 2011b).