Earth Science (EARTH-1141) - Volcanoes Vocab

Chapter 6: Volcanoes and Other Igneous Activity

effusive eruptions

a quiescent (inactive) eruption that produces mainly outpourings of fluid lava

viscosity

measure of fluids resistance to flow

eruption columns

buoyant plumes of hot, ash-laden gases that can extend thousands of meters into the atmosphere

aa flow

a type of ava flow that has a jagged, blocky surface, slow moving chunky pieces

pahoehoe

lava flow with smooth-to-ropey surface

lava tubes

a tunnel in hardened lava that acts as a horizontal conduit for lava flowing from a volcanic vent

pillow lava

lava that solidifies underwater and develops the structure that resembles a piles of pillows when __outer skin solidifies quickly due to water__

volatiles

gaseous components of magma dissolved in magma; readily vaporize at surface pressures

pyroclastic materials

volcanic rock ejected during an eruption including ash, bombs, and blocks that range in size from dust to to pieces that weigh several tons

scoria

hardened lava that has retained the vesicles produced by escaping gases

pumice

light colored glassy vesicular rock commonly having a granitic composition

fissure

crack in rock along which there is a distinct separation which volcanic activity frequently begins with

conduit

pipelike opening through which magma moves towards Earth’s surface that terminates at a **vent**

vent

the surface opening of a **conduit**

volcanic cone

cone shaped structure built by successive eruptions of lava or **pyroclastic materials**

crater

the depression at the summit of a volcano

caldera

large **depression** typically caused by collapse or ejection of the summit area of a volcano

parasitic cone

volcanic cone that forms on the flank of larger volcanoes

fumarole

vent in a volcanic area from which ONLY fumes or gases escape

shield volcano

broad, gently sloping volcano built from fluid basaltic lavas, that usually begin as **seamounts**

seamount

isolated volcanic peak on the deep sea ocean floor

cinder cone

rather small volcano built primarily of pyroclastics ejected from a single vent

composite volcano

large, nearly symmetrical volcano composed of both lava flows and pyroclastic material; aka stratovolcano

pyroclastic flow

highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground

lahar

mudflow on the slope of a volcano that results when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels; may occur even when volcanoes are *not* erupting

fissure eruption

eruption in which lava is extruded from narrow fractures or cracks in the crust

basalt plateau

broad and extensive accumulation of lava from a succession of flows emanating from fissure eruptions

flood basalts

flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thickness of hundreds of meters

volcanic neck

isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano

host rock

preexisting crustal rocks intruded by magma; may be displaced or assimilated by magmas

intrusions

structure that results from the emplacement and crystallization of magma beneath the surface of the Earth

tabular

describing a feature such as an igneous **pluton** that has two dimensions that are much longer than the third

massive

refers to an igneous **pluton** that is not tabular in shape.

discordant

plutons that cut across existing rock structures

concordant

term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock