Morne Watt is a stratovolcano

Stratovolcano

A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 in the south of the island of Dominica

Dominica

Dominica , officially the Commonwealth of Dominica, is an island nation in the Lesser Antilles region of the Caribbean Sea, south-southeast of Guadeloupe and northwest of Martinique. Its size is and the highest point in the country is Morne Diablotins, which has an elevation of . The Commonwealth...

. It rises to a height of 1,224 m (4,016 ft) and is the third highest peak in Dominica (after Morne Diablotins

Morne Diablotins

Morne Diablotins is the highest mountain in Dominica, an island-nation in the Caribbean Lesser Antilles. It is the second highest mountain in the Lesser Antilles, after La Grande Soufrière in Guadeloupe...

 and Morne Trois Pitons). A major eruption from Morne Watt producing pyroclastic flows took place about 1300 years ago. A moderately large phreatic eruption

Phreatic eruption

A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...

 took place at the Valley of Desolation thermal area NE of Morne Watt in 1880, when volcanic ash

Volcanic ash

Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...

 fell over a 4-km-wide sector at the coast, 10 km (6 mi) from the vent. A smaller phreatic eruption, and the most recent eruption, occurred in July 1997, when ashfall was confined to the Valley of Desolation area. It had a VEI of 1

Volcanic Explosivity Index

The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....

.
These eruptions mark the only known historical eruptions on the island of Dominica.