The Soufriere Hills Volcanic Eruption

On Monday, July 28, 2008, at approximately 11:45 pm, the Soufriere Hills Volcano in the West Indies on the island of Montserrat erupted, resulting in a large ash plume that could be followed for miles on satellite imagery. This particular volcano is very active and often emits ash into the atmosphere on a regular basis. The last major eruption on the island was back in mid-July 2003 causing portions of its volcanic dome to collapse and creating huge pyroclastic flows (fast-moving clouds of hot ash and rock) that spread 2 kilometers out over the ocean.

In this latest event, the Soufriere Hills Volcano emitted ash several thousand feet into the atmosphere overnight. The animated satellite image below clearly shows the eruption. For your reference, the island of Montserrat is labeled with the four-letter identifier: TRPG. This is the identifier for Gerald's Airport located on the island. As you watch the satellite loop, you will see ash spreading west, southeast, and northwest from the island.

As the ash rises from the volcano, it begins to encounter various wind currents at different levels in the atmosphere. The 1200Z upper air sounding from San Juan, Puerto Rico is depicted. On the right side of the sounding plot, you can see where the winds are originating throughout the depth of the atmosphere. In the lowest levels of the atmosphere, winds are out of the east. In the mid-levels of the atmosphere, winds are out of the southeast. In the upper levels of the atmosphere, winds are out of the northwest. These differing wind directions make up what forecasters coin directional wind shear. So, as the volcanic ash encountered each of these atmospheric levels, it responded by being blown in the direction the wind was traveling.

Following the volcanic ash from the island of Montserrat northwestward toward the U.S. Virgin Islands and Puerto Rico, you can see this mid-level ash interacting with mid-level moisture causing brief shower formation (in the form of colder cloud tops depicted at 1015Z between St. Maarten (TNCM) and St. Thomas (TIST) before succumbing to the surrounding drier air.

Volcanic ash can be extremely dangerous, not only to your respiratory health, but also to aircraft. Ash that gets ingested into airplane engines can cause serious damage to the engine itself. The National Weather Service in San Juan, in conjunction with the Volcanic Ash Advisory Center in Washington DC, and area airports within Puerto Rico and the U.S. Virgin Islands, have fostered partnerships to ensure that the people we serve stay safe. At the moment this volcanic ash was detected, area airports were alerted to its presence so that customers such as airlines can take the appropriate actions to protect life and property.