La Soufrière Integrated Volcanic Hazard Zones

Present La Soufrière Alert Level:ORANGEThere is a highly elevated level of seismic and/or fumarolic activity or other unusual activity. An eruption may begin with less than twenty-four hours’ notice.

The Integrated Volcanic Hazard Zones for the La Soufrière Volcano was developed for designing an emergency plan for effective management of the Soufrière Volcano. Zones were assigned based on the projected effect of an explosive eruption, with some consideration of a long-term and large-scale explosive eruption.

Content:
Hazard Zone 1 – Red Level
Hazard Zone 2 – Orange Level
Hazard Zone 3 – Yellow Level
Hazard Zone 4 – Green Level

Hazard Zone 1 – Red Level

Volcanic Hazard Map for the La Soufrière Volcano, St. Vincent (UWI SRC/NEMO)
Volcanic Hazard Map for the La Soufrière Volcano, St. Vincent (UWI SRC/NEMO)

What does this mean?

This includes all areas expected to experience maximum damage in the short term and is the zone where all hazardous events have their greatest influence. It is defined by the zone of expected total destruction from pyroclastic flows, surges, and mudflows and by the zone of maximum expected damage from all projectiles. This zone is likely to experience more than 30 centimeters of ash. During the course of an eruption, this zone would be unsuitable for human habitation.

Hazard Zone 2 – Orange Level

What does this mean?

This includes all areas of moderate pyroclastic flow and surge hazard, areas within the 5-kilometer projectile zone, and areas likely to experience between 10 and 30 centimeters of ashfall. These areas will be affected similarly as Zone 1 during large scale eruptions.

Hazard Zone 3 – Yellow Level

What does this mean?

This zone will be free from the effects of flows and surges but will be affected by 5 to 10 cm thick ash falls, minor earthquakes, and lightning strikes. This zone will experience significantly less physical damage than Zones 1 and 2.

The 10 cm ash isopach for the 1902 eruption is taken as the cut-off point between this zone and integrated hazard Zone 2. The area of Zone 3 will experience less physical damage than Zones 1 and 2. Damage to flora will probably be restricted to the foliage with root systems left intact. Despite a relatively minor impact on the physical infrastructure, hazardous events may still cause major problems for the human population. The area will be included within the zone of total devastation during eruptions expected in the long term.

Hazard Zone 4 – Green Level

Volcanic Hazard Map for the La Soufrière Volcano, St. Vincent (UWI SRC/NEMO)
Volcanic Hazard Map for the La Soufrière Volcano, St. Vincent (UWI SRC/NEMO)

What does this mean?

This zone includes areas likely to be relatively safe from hazardous events, except for minor ashfall of less than 5cm. Crop damage and water supply disruption due to ashfall will be the main effect, but other physical damage will be minimal.

The map only shows the hazard zone on land. However, lahars and pyroclastic falls, flows and surges will also impact areas offshore to varying degrees, and as such, the hazard zones must be envisaged as extending some distance offshore.

However, in areas close to the boundary with zone 3 the physical signs of volcanic activity may cause some anxiety to the local population.

Zone 4 will be relatively safe from hazardous events. In areas located south of this zone, infrequent heavy ashfall may occur due to exceptionally strong local winds. In these areas, the eruption’s impact will be felt only in terms of the additional burden placed on resources by people evacuated from higher risk zones further north.

In a long-term eruption, these areas will be more strongly affected by ashfall. They may remain largely unaffected during the first few months of activity but will become increasingly impacted with time, due to the
accumulation of ashfall.

The U.W.I. Seismic Research Centre is the official source of information for earthquakes and volcanoes in the English-speaking Eastern Caribbean. The SRC is the scientific monitoring agency that supports various local disaster management agencies of the Eastern Caribbean. This includes the monitoring of the La Soufrière Volcano.

The Seismic Research Centre (SRC) updates the National Emergency Management Organization (NEMO) of St. Vincent and the Grenadines which is then responsible for adjusting the alert level of La Soufrière based on the SRC’s information. NEMO is then responsible for coordinating evacuations across the hazard zones based on the alert level and volcanic hazard.

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