View of ash falling to the ground from the back yard of a house on the Island of Montserrat. The ash began falling in the early afternoon, minutes after nearby Soufriere Hills volcano generated a pyroclastic flow and explosion from an erupting lava dome. Ashfall can cause partial or complete darkness by blocking sunlight. Depending on several factors, including the size and duration of an eruption, strength and direction of the wind, and distance from the volcano, an area may experience dark conditions for as little as a few minutes or as long as 1-3 days.

Because falling ash may cause power facilities to shut down or interrupt power transmission, there may not be electrical power for lights in homes, businesses, and along roads. As part of an emergency kit, flashlights (stored with extra bulbs and batteries), candles, and gas-powered laterns may be the only means of being able to see in total darkness.