5: volcanoes and volcanic hazards Flashcards
the two factors that determine the nature of a volcanic eruption
magmas viscosity and gas content
volcanoes erupt
lava, gases, and solid pyroclastic material
roughly viscosity basaltic lava can flow ____ distances
great
when lava erupts underwater and the outer surface is instantly chilled while the inside continues to flow, it creates
pillow lavas
gases most commonly emitted by volcanoes
water vapor and carbon dioxide
gases that rapidly expanded upon reaching the earth’s surface that generate a mass of lava fragments
pyroclastic materials
bubbles of gas in lava preserved as voids in rocks called
vesicles
spots on volcanoes where only gas is expelled
fumaroles
most shield volcanoes begin as
seamounts
successive flows of low viscosity basaltic lava and lack of pyroclastic debris
shield volcano eruption
consists of pyroclastic material and lava flows
composite volcano
classic symmetrical cone shape
composite volcanoes
erupts silica rich magmas of andesite or rhyolite
composite volcano
volcano eruptions greatest threat to humans
pyroclastic flow
a mix of hot gas and pyroclastic materials that race downhill at great speeds and incinerate anything and everything in it’s path
pyroclastic flow
the welded deposit of pyroclastic materials
welded tuff
steep sided structures composed mainly of pyroclastic debris and a basaltic composition
cinder cone volcano
cinder cones easily succumb to
weathering and erosion
volcano that forms from multiple erosions over millions of years
composite volcano
mudflows that form on volcanoes that are rapidly moving ash and debris that suspend in water and follow stream valleys
lahars
volcanoes that erupt at sea level can cause
tsunamis
forms when the lava above a magma chamber can’t be supported and collapses causing a broad depression
caldera
on what volcano does a caldera form slowly as lava drains from magma chambers beneath the volcano?
shield volcano
on what volcano does a caldera collapse often follow an explosive eruption?
composite volcano
volcanos form at both
convergent and divergent boundaries
convergent boundaries that involve the subduction of oceanic crust are the most common site for
explosive volcanos
what are large cracks in the crust called?
fissures
thick masses of high viscosity silica rich lava that accumulates in the summit crater or caldera of a composite volcano
lava domes
a column of mantle rock that is warmer and more buoyant than the surrounding mantle
mantle plume
