Chapter 12 Flashcards
volcanic geosystem
the rocks, magma, and processes needed to describe the entire sequence of events from melting to eruption
three types of lava
basaltic
andesitic
rhyolitic
basaltic lavas
most common magma type
product of mantle melting
erupt when hot, fluid magmas fill up a volcano’s plumbing system and overflow
pahoehoe
forms when a highly fluid lava spreads in sheets
andesitic lava
lower temperatures than basalts
higher silica content - flow slower
rhyolitic lava
lowest melting point
richest in silica
tuffs
rocks created from smaller fragments such as ash
breccias
rocks created from larger fragments
types of central-vent volcanoes
shield domes cinder cones stratovolcanoes craters calderas diatremes
shield volcano
example
occurs when basaltic lava flows create a shield-shaped volcano 2+ kilometers high and tens of kilometers in circumference
example - Mauna Loa
volcanic dome
occurs when andesitic and rhyolitic flows (very viscous) are essentially squeezed out of the volcano with very little lateral spreading
cinder cones
these are created when volcanic vents discharge pyroclasts that build up to create a cone
vent can become filled with volcanic debris that falls down the slope
what is an angle of repose?
the maximum angle at which fragments in a cinder cone will remain stable rather than sliding down the slope
stratovolcano
occur when alternating lava flow of lava and pyroclasts build a concave-shaped composite volcano
crater
a bowl shaped pit found at the summit of most volcanoes
calderas
when a lot of magma leaves the magma chamber, the chamber can’t support the roof so the roof collapses
can form a lake
yellowstone
diatreme
when breccia fills the vent and channel below it after an explosion
fissure eruptions
volcanic eruptions that come through vertical cracks in the Earth’s surface
flood basalts
when successive flows of highly basaltic lava piles up
ash-flow deposits
sheets of hard volcanic tuffs that come from pyroclast eruptinos
at what type of plate boundaries are most volcanoes found?
convergent (80%)
where do most fissure eruptions occur?
along mid-ocean ridges
what forms when oceanic crust subducts below continental crust?
subduction zone volcanoes form volcanic mountain belts on land such as the Andes
what forms when overriding lithosphere is oceanic?
subduction zone volcanoes form volcanic island arcs such as the Aleutian Islands
intraplate volcanism
volcanoes far from plate boundaries
hot spots
intense, localized volcanism far from a plate boundary
how are hot spots formed?
hot, solid material rises through narrow jets from deep within the mantle
mantle plumes
narrow jets of hot solid material that rise from deep within the mantle
volcanic hazards
lahars
flank collapse
caldera collapse
eruption clouds
what are lahars and how do they occur?
torrential flow of wet volcanic debris
occur when pyroclastic flows meet a river or snow bank or when a lava flow meets glacial ice
flank collapse
the collapse of the side of a volcano
occur four times per century
if they occur underwater it can cause a tsunami
eruption clouds
ash clouds than can damage airplanes
how can eruptions be predicted
instruments monitor signals from earthquakes, swelling of the volcano, and gas emissions
