the character flow of lava flows reflects its viscosity: incandescent stream, builds into a fast moving rubble cover mound or oozes out like a sticky scalding paste. Basaltic/rhyolitic
What is Basaltic lava flows?
Basaltic (mafic) lava has very low viscoity because it contain very little silica and is very hot
What is a lava tube?
An insulated, tunnel-like conduit within a flow, through which lava moves
What is a pahoehoe?
Flows with warm, pasty surfaces wrinkle into smooth, glassy, rope like ridges
What is an a'a'?
If the surface layer of the lava freezes underneath, it becomes a jumble of sharp, angular fragments, creating a rubbly flow. It is foot slashing
What is columnar jointing?
During the final stages of cooling, lava flows contract and may fracture into roughly hexagonal comumns.
What is andesitic lava flow?
because of its higher silica content and thus its greater viscosity, andestic lava cannot flow as easily as basaltic lava. it first forms a large mound above the vent. moves up the surface to form a jumble of rubble.
What is Rhyolitic lava?
is the most viscous of all lavas because it is the most silicic and the coolest. It tends to accumulate either bove the vent in a dome-like maass, called a lava dome, or bulbous less than 2km long. Where they do form they have broken and blocky surfaces.
What is volcaniclastic deposits
A layer composed of fragments of igneous material (tephra, ash, bombs) erupted from volcanos
What is pyroclastic debris?
which forms from lava that flies into the air and freezes. Also includes the debris formed when an eruption blasts apart preexisting vocanic rock that surrounds the volcanos vent, and the drbris that accumulate after tumbling down the vocano in landslides or being transported in water rich slurries
What does volcanic gas consist of?
most magma contains dissolved gases, including water, carbon dioxide, sulfur dioxide, and hydrogen sulfer
What is a magna chamber?
a space below ground filled with magma
What is a fissure?
conduit to the crust that is cracked.
What is a caldera?
After major eruptions, the center of the volcano may colapse into the large, drained magma chamber below. a big circular depression up to 1000's of meters across and up to several hunder meters deep.typically has steep was and a flat bottom. most notable is crater lakes in oregon
What is the difference between calderas and craters?
they differ in terms of size, shape and mode of formation
What are the names of the difference in the shapes of above ground volcanoes?
shield, cinder and composit volcanos
What is a shield volcano?
resembles a soldiers shield lying on the ground. they are generally low viscosity baslatic lava flows
What are cinder cones?
consist of cone shaped piles of tephra. Symmetrical and have deep craters at their summit
What are composite volcanos?
large and cone shapped (steaper near the summit), and consist of alernating layer of lava, tephra and debris. Mt. Fuji.
What are effusive eruptions?
produce mainly lava flows. low viscosity basaltic lavas which can stream ten of hundreds of km. lava may pool in lakes or spray up in fountains.
What are explosive eruptions?
produce clouds and avalancehes of pyroclastic debris. the pressure becomes so great that it blasts the lava. in ome cases it leaves behind a caldera. The resulting plume of debris resembles the musroom cloud above a nuclear explosion.
Where do most above ground volcanos lie?
along convergent plate boundaries (subduction zones)