The Ghost Capital of the Caribbean: How the Soufrière Hills volcano buried an entire city in minutes

In 1997, Soufrière Hills erupted and entombed the city of Plymouth on the island of Montserrat. The capital, which was once a bustling centre for commerce, was covered in many feet of ash and debris within a few hours, leading to a permanent evacuation.

The Montserrat Volcano Observatory states that over 80 per cent of Plymouth's infrastructure was destroyed due to the eruptions. Even though Plymouth is now an uninhabitable Exclusion Zone, it is legally still the island's capital today. The city has been compared to a ‘Modern Pompeii’ and serves as a reminder of the destructive effects of geology; it has also provided scientists with valuable information about how volcanoes affect and displace modern civilisation over time.

How the Soufrière Hills volcano wiped Plymouth off the map

The destruction of Plymouth was primarily caused by pyroclastic density currents (PDCs)- gravity-driven clouds of hot gas and rock. Research published by the U.S. Geological Survey (USGS) and the Montserrat Volcano Observatory (MVO) indicates these flows reached temperatures exceeding 400 degree Celcius (752 degrees Fahrenheit) and travelled at speeds over 100 miles per hour. The PDC flows behaved like fast-moving liquids, and due to the fluidised nature of these high-velocity currents, they were able to completely cover buildings from their base to their second floor with a densely packed matrix of fine ash and tephra.

In so doing, this rapid burial preserved Plymouth in a frozen state, thus providing archaeologists with the opportunity to study ash and volcanic mud from everyday items of 20th-century life.

These artefacts represent a unique, but fragile, means by which archaeologists will gain knowledge about life in the Caribbean during the 20th century.

How the MVO monitors structural decay in a restricted zone

Plymouth, the de jure (legal) capital of Montserrat, has been destroyed, including all of the infrastructure in the city.

However, the Government of Montserrat notes that although the Government has moved its administrative functions to the north of the island in Brades, Plymouth's legal status as the official seat of the Government is still preserved in the constitution and other records. The southern half of Montserrat is designated as the Zone V Exclusion Area and cannot be accessed without a police escort due to the continuing threat from the volcano.

This ongoing and complete legal and physical isolation of the city allows the Montserrat Volcano Observatory (MVO) to use GPS and seismic sensors to study the accelerated structural failure and corrosive loading from the weight and chemical acidity of the volcanic tephra.

How Volcanic tephra reshaped Montserrat's topography

According to research from the Journal of the Geological Society, the large amount of volcanic material deposited into Plymouth permanently reconfigured the Island’s topography and expanded its coastline.

The ash layers, which reach over 12 meters (39 feet) thick in some areas, have changed the drainage basins and coastline of the Island. In addition, the high porosity of the volcanic tephra acts as a thermal insulator; therefore, combined with the lack of light, it creates a slow decay rate for all organic materials and household artefacts that may be buried beneath it.Based on data from NASA Earth Observatory, these environmental changes have produced specialised pioneer plant species in the exclusion zone and provide a unique model of biological succession in a post-eruption tropical environment.