dacite Dacite is a type of volcanic rock that is light-colored and rich in silica (63 to 68 percent).

debris avalanche A debris avalanche is a sudden rock/soil/debris slide and flows with great speed from a volcano.

debris flow A debris flow (also called a mudflow or lahar) is a moving mixture of rock, water, and other debris.

decibel Decibels (abbreviated dB) are the unit of measuring the loudness (or intensity) of sounds. 0 dB is the faintest audible sound. The decibel scale is logarithmic. Blue whale calls are up to 188 dB; this is the loudest animal sound, and is painful to the human ear. Volcano eruptions are one of the loudest sounds on Earth and are over 272 dB.

degree A degree is a measure of temperature or angle.

diatreme A diatreme is a volcanic vent or pipe that is formed by gas-charged magma.

dike A dike is a sheet-like intrusion of magma (molten rock) that froces its way through a layer of fractured rock. The magma flows through cracks in the rock and later cools and solidifies into a sheet of igneous rock.

dome A lava dome is a dome-shaped mound that is formed around a vent by viscous lava.

dormant volcano A dormant volcano is a volcano that is not active now, but may erupt in the future.

dust Volcanic dust is a solidified lava that is tiny particles. It is ejected from volcanos during an eruption.