magma chamber any underground cavity holding magma.
magnitude the power, measured by numerical value, of an earthquake.
monogenetic designating a volcano that formed in a single eruption.
monticule a secondary volcanic cone of a volcano. mudflow see lahar.
nuee ardente French term for a fiery cloud or superheated mass of gas and clastic material, considered to be the most devastating weapon in a volcano's arsenal. The cloud fries flesh and carbonizes wood on contact and literally sterilizes the landscape. Often hot enough to melt iron and moving as fast as 100 miles per hour, it has been described as a napalm explosion and gas attack rolled into one.
obsidian volcanic glass.
pahoehoe Hawaiian term for smooth-textured lava with the appearance of congealed molasses.
paroxysm an eruption of extreme violence and magnitude.
Pele's hair strands of spun glass, created by blow- off from fountains or cascades of lava.
Pele's tears tear-shaped drops of glass formed with Pele's hair.
phreactic explosion an explosion of steam caused when water and hot volcanic rock meet.
pillow lava pillow-shaped blobs of lava, formed underwater.
pipe a vertical magma conduit.
pit crater a crater that forms not from venting or eruption but from sinking of the ground.
plastic that which can be molded, such as lava or magma.
plate tectonics the interplay of the 10 massive fragments or plates of Earth's broken crust, forcing continents to migrate and new crust to be formed, all related to volcanic activity.
plug the solidified lava that fills the throat of a volcano. Highly resistant to erosion, the plug may remain standing as a solitary pinnacle after the outer shell of the mountain or volcano has worn away.
plug dome a mound of hardened lava that fills and caps a vent.
pluton a large igneous mass formed deep in Earth's crust.
polygenetic forming through many eruptions.
pumice a light, porous stone frequently ejected by volcanoes and known for its ability to float on water.
pyroclastic flow an avalanche of hot gas and ash.
pyrotechnics the "fireworks" caused by a volcano.
repose the period of time between eruptions.
rhyolite a light-colored volcanic rock comprised of silica, potassium, and sodium.
rift system the ocean ridges where new crust is formed and Earth's tectonic plates are drawn apart.
Ring of Fire a ring of high earthquake and volcanic activity that extends around the Pacific Ocean.
scoria a type of bomb that is filled with air cavities yet is heavier than pumice.
seafloor spreading the expansion of the seafloor along ridges, and the creation of new crust with the separation of Earth's tectonic plates.
seamount a mountain or volcano under the sea.
seismograph a device that senses and records vibrations of the Earth.
shield volcano the largest type of volcano (such as those found in Hawaii) but the least explosive due to a low silica content.
skylight an opening in the roof of a lava tube.
solfatara a fumarole that emits sulfurous gases.
spatter cone a pile of basaltic material forming a cone over a fissure or vent.
stratovolcano a volcano that emits lava and ejects rock matter.
subduction zone the ridge where two tectonic plates meet and one overrides the other.
talus a slope comprised of broken rocks.
tephra collective term for all elastic material ejected in an eruption, from sand-sized particles to chunks of rock 200 feet wide.
tilt the slope of a volcano's flank as measured against itself in the past or against another reference point.
tiltmeter a vulcanist's tool for measuring the growth rate of a bulge in the side of a volcano.
tremor continuous seismic activity due to the flow of magma.
tsunami a massive ocean wave formed by an earthquake or a volcanic eruption, or sometimes when an entire flank of a volcano collapses into the sea. A tsunami can travel from one side of an ocean to another.
tuff rock formed from volcanic activity.
tumulus a hardening sheath of cooling lava that forms over a hotter, flowing river of lava below.
vent any opening through which hot gas or molten materials escape.
volcanic pipe a large shaft of solidified magma, topped by a crater; a rich source of diamonds and other gems.
volcanic winter a drop in worldwide temperature due to volcanic activity, especially that which obscures part of the sky and the Sun's rays with volcanic ash.
volcanologist a scientist who studies volcanoes and volcanic activity. Also known as a vulcanist.
vulcanist see volcanologist.
Vulcanus the Roman god of fire.
wind and storms
Aeolus the Greek god of wind.
anemometer three-cupped device that rotates with the wind to measure its velocity.
backing wind a wind that gradually shifts counterclockwise through the compass; the opposite of a veering wind.
Beaufort scale a scale in which wind speeds are assigned the code numbers 0 to 12, corresponding to "calm" to "hurricane."
blustery National Weather Service's descriptive term for winds from 15 to 25 miles per hour; interchangeable with breezy and brisk.
breeze classification light—4 to 7 mph; moderate—13 to 18 mph; fresh—19 to 24 mph; strong—25 to 31 mph; gale—39 to 46 mph; strong gale—47 to 54 mph; storm wind—55 to 63 mph; violent storm wind—64 to 72 mph; hurricane—73 and up (mph = miles per hour).
breezy National Weather Service's descriptive term for winds from 15 to 25 miles (24-40 km) per hour. Also known as blustery and brisk.
brisk National Weather Service's descriptive term for winds from 15 to 25 miles (24-40 km) per hour. Also referred to as blustery and breezy.
cat's paw any slight breeze that lightly ripples the sea's surface.
chinook any warm dry wind descending the leeward slope of a mountain; known as a foehn in Europe.
chubasco a violent squall on the west coast of tropical and subtropical North America.
condensation funnel a funnel cloud comprised of condensed water droplets.
cordonazo hurricane-borne wind blowing from the south on the west coast of Mexico.
Coriolis force force resulting from the Earth's rotation, which causes and deflection.
cyclone a massive rotating storm measuring hundreds or thousands of miles across, turning counterclockwise above the equator and clockwise below, generally less violent than a hurricane.
derecho a very large and powerful windstorm spawned by a line of thunderstorms. Derechos usually stretch for 250 miles (460 km) or more and are characterized by sustained winds from at least 58 miles per hour (92 km/hr) to an excess of 100 miles per hour (160 km/hr).
doldrums steamy equatorial regions with dead-calm winds and flat seas.