La Soufrière’s Volcanic Ash – What You Need To Know

The La Soufrière Volcano erupting at approximately 2:45 PM Friday 9th April 2021 sending a large column of volcanic ash into the atmosphere (UWI SRC)

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.

What is Volcanic Ash?

Volcanic ash is not the product of combustion, like the soft fluffy material created by burning wood, leaves, or paper, but rather consists of fragments of rocks, minerals, and volcanic glass ranging in size from sand to clay-like (from 2 mm (1/12 in) to less than 0.004 mm (1/256th in) in diameter). Ash is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water. Ash is spread over broad areas by the wind.

Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere. The gasses’ force shatters the magma and propels it into the atmosphere, where it solidifies into fragments of volcanic rock and glass.

Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions (eruptions that arise from interactions between water and magma), causing the water to explosively flash to steam leading to the shattering of magma. Once in the air, ash is transported by wind up to thousands of kilometers away.

Why is the volcanic ash moving to the east?

NOAA's HYSPLIT Model showing a potential scenario for ash dispersal in the atmosphere. (NOAA)
NOAA’s HYSPLIT Model showing a potential scenario for ash dispersal in the atmosphere. (NOAA)

Since the start of the La Soufrière Volcano’s explosive eruption, volcanic ash has been dispersing in different directions in the atmosphere. Given in the Lesser Antilles, winds move from the east to west, why is the ash being blown to the east?

Depending on the ash column’s height, winds at different heights of the atmosphere can carry layers of ash in different directions. To determine where the ash may travel, scientists look at numerical weather prediction models to determine wind speeds and directions at different heights.

Diagram explaining why Barbados is getting ash, even though St. Vincent is to our west!

Posted by Barbados Meteorological Services on Saturday, April 10, 2021

At low levels of the atmosphere in the Caribbean, generally meaning below 4,000 to 6,000 feet, winds move from east to west, known as our trade winds. Volcanic ash at this level of the atmosphere will generally take a westward path before landing on the ground or the surface of the ocean. It should also be noted that winds at this level are relatively weaker than other levels of the atmosphere in typical conditions, with winds usually between 0 to 30 knots, generally remaining below 15 knots. This relatively slower wind speed means that ash at low levels of the atmosphere travels smaller distances.

Volcanic Ash Advisory issued at 1:43 AM Saturday 10th April 2021 from the Washington DC Volcanic Ash Advisory Center for the La Soufrière Volcano
Volcanic Ash Advisory issued at 1:43 AM Saturday 10th April 2021 from the Washington DC Volcanic Ash Advisory Center for the La Soufrière Volcano

At the mid- and upper-levels of the atmosphere in the Lesser Antilles, winds are typically from the west (including northwesterly and southwesterly winds). This means that the ash at higher levels of the atmosphere will generally travel eastward, towards the southeast and northeast, depending on prevailing weather features. It is also important to note that winds at these levels are much stronger, ranging between 0-60 knots, at times higher. These faster wind speeds allow ash to be dispersed at much greater distances high in the atmosphere.

Can La Soufrière’s ashfall impact T&T or Grenada?

For ash to travel southward, winds will have to originate from the north. This is a highly unusual circumstance only seen when powerful low-pressure systems such as tropical cyclones move across the region, influencing wind speeds and directions across the Windward Islands.

Through the next 14 days, models indicate mostly easterly winds below the 500 millibar level and mostly westerly winds above the 500 millibar level. Hence the islands most at risk for ashfall remain, St. Vincent, St. Lucia, Barbados, and Martinique.

If winds at the mid to upper levels of the atmosphere shift toward the south-southwest, ashfall will be possible across Grenada’s dependencies including Carriacou and Petit Martinique, as well as several small, largely uninhabited islands. Similarly, as ash drifts further and further southeast over time, it is possible eastern areas of Tobago experience some ashfall by next week (April 12th-19th). For Trinidad, it still remains highly unlikely ash may travel as far south as the island.

Respiratory Protection From La Soufrière’s Volcanic Ash

The Caribbean Public Health Agency has provided tips on how to protect respiratory system from volcanic ashfall.

What to do if volcanic ash is falling?

Tips from the Barbados Meteorological Service on what to do and not do during volcanic ashfall.
Tips from the Barbados Meteorological Service on what to do and not do during volcanic ashfall.

The National Emergency Management Organization (NEMO) of St. Vincent and the Grenadines are advising Vincentians who experienced heavy ashfall today: “Now that the La Soufriere volcano has begun erupting explosively, ash falls will soon overwhelm us. Be sure to get rid of or clean up the ash soon after it falls. If rain falls, the ash could harden and pose a danger.”

For those that may experience volcanic ash falling on your vehicles or glass surfaces, do not use wipers to remove the ash as the abrasive ash will scratch glass. Instead, use water and clean off gently.

For more on the hazards on volcanic ashfall, visit the International Volcanic Health Hazard Network.

Volcanic Ash Advisory issued at 1:43 AM Saturday 10th April 2021 from the Washington DC Volcanic Ash Advisory Center for the La Soufrière Volcano
Volcanic Ash Advisory issued at 1:43 AM Saturday 10th April 2021 from the Washington DC Volcanic Ash Advisory Center for the La Soufrière Volcano

The Marine & Aviation Hazard

The explosive eruption of the La Soufrière Volcano has emitted significant volumes of ash into the atmosphere that is affecting mainly St. Vincent and Barbados.

On the ground, volcanic ash can cause discomfort in persons suffering from respiratory ailments, impact water resources, affect the power grid and cause damage to homes and vehicles. An ashfall that leaves a thick layer of ash may cause roofs to collapse, clog gutters, and interfere with air conditioning units.  For both people and animals, it can cause eye, nose, and lung irritation, as well as breathing problems. Animals in an area coated by volcanic ash may have difficulty finding food, as the plants in the region may be covered in ash. These impacts are likely across St. Vincent.

In the air, ash particles can abrade forward-facing surfaces, including windscreens, fuselage surfaces, and compressor fan blades. For the aviation industry, regular “Volcanic Ash Advisories” and “Significant Meteorological Information” are being issued by the Washington DC Volcanic Ash Advisory Center and the Trinidad and Tobago Meteorological Service, respectively. Caribbean Airlines has canceled flights originating and landing in Barbados, as well as St. Vincent.

On the ocean, volcanic ash can clog air intake filters in a matter of minutes, crippling airflow to vital machinery. It can be corrosive to metal or other exposed shipboard equipment. Certain types of volcanic ash do not disperse easily in water; instead, clumping on the surface of water bodies in pumice rafts. These rafts can clog salt-water intake strainers very quickly, which can result in overheating of shipboard machinery dependent on seawater service cooling.
Ashfalls can reduce visibility to less than 1/2 mi (800 m), which is a hazard to navigation. This, combined with the above three other main impacts, make sailing in the vicinity of volcanic ash very dangerous for mariners.

Ashfall Advisory in effect for marine areas surrounding St. Vincent and Barbados, well north and east of Trinidad and Tobago. (National Hurricane Center - Tropical Analysis and Forecast Branch)
Ashfall Advisory in effect for marine areas surrounding St. Vincent and Barbados, well north and east of Trinidad and Tobago. (National Hurricane Center – Tropical Analysis and Forecast Branch)

For mariners, an “Ashfall Advisory” is in effect for the marine waters surrounding St. Vincent and extending as far east as east of Barbados from the National Hurricane Center Tropical Analysis and Forecast Branch. Mariners are encouraged to contact the National Hurricane Center at 305-229-4424 if they encounter volcanic ash or floating volcanic debris.

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