Quiz (Chapter 5 and 6) Flashcards
(53 cards)
magma
molten rock that usually contains some crystals and varying amounts of dissolved gas
lava
erupted magma
viscosity
mobility
The more viscous = greater resistance to flow
influenced by: temperature, composition, and dissolved gases
Temperature
As lava cools it congeals and the viscosity increases
Composition
chemical composition of the magma
Mafic
Basaltic magma that contains about 50 percent silica
intermediate
Andesitic magma contains about 60 percent silica and form rocks such as andesite and diorite
Felsic
Rhyolitic magma contain more than 70 percent silica and produce rocks such as granite and rhyolite
The more silica in the magma….
the greater the viscosity
Dissolved gases
mainly dissolved water which increases the fluidity
gases also give magma their explosive characteristic
Quiescent Eruptions
On the ocean floor high temperature basaltic magmas reach Earth’s surface, where they produce highly fluid lavas.
In continental settings, the density of the crustal rock is less than that of the ascending material causing the magma to pond at the crust-mantle boundary
Explosive Eruptions
all magmas contain some water vapor and other gasses that are kept in solution by the immense pressure of the over lying rock. As the magma rises, a reduction in pressure occurs and the dissolved gases begin to separate from the melt forming tiny bubbles
ex: opening a soda can
eruption columns
highly viscous magmas expel particles of fragmented lave and gases at nearly supersonic speeds that evolve into bouyant plumes
lava flows
the vast majority of lava on Earth (more than 90%) is basaltic (mafic) andesitic (intermediate) lava (less than 10%) rhyolitic (felsic) less than 1%
hot basaltic lavas
usually very fluid, flow in thin broad sheets or stream-like ribbons and move very fast
Aa and Panhoehoe flows
aa: rough jagged surfaces of rough jagged blocks with dangerously sharp edges and spiny projections
pahoehoe: smooth surfaces that sometimes resemble twisted braids of ropes, hotter and more fluid and can change into aa flows in lava tubes
lava tubes
cave-like tubes that were previously conduits for carrying lava from an active vent to the flow’s leading edge
pillow lava
occurs over and over as molten basalt is extruded like toothpaste from a tightly squeezed tube. stacked one atop the other
pyroclastic materials
pulverized rock and lava fragments from the vent also known as tephra
pumice
low density vesicular rock that forms during explosive eruptions of viscous magma having an andesitic to rhyolitic composition
Anatomy of a volcano
conduit:localized path of gas-rich magma that moves up through a fissure into circular chamber
vent: surface opening
volcanic cone: cone-shaped wall structure created by successive eruptions of lava and/or pyrocastic material
crater: located at the summit of most volcanic cones is a somewhat funnel-shaped depression
parasitic cones: flank eruption secondary vent
shield volcanoes
broad slightly dome-shaped
covers large areas
produced by mild eruptions of large volumes of basaltic lava
Most begin on the seafloor as seamounts; only a few grow large enough to form a volcanic island
Ex: Hawaiian Islands, the Canary Islands, the Galapagos, and Easter Island
Mauna Loa is the largest shield volcano on Earth
Cinder Cone volcanoes
built from ejected lava fragments that begin to harden in flight to produce the vesicular rock scoria
frequently occur in groups
Lava fields
Paricutin
Composite volcanoes
most are located near the Pacific Ocean (ring of fire) contain alternating layers of explosively erupted cinders and ash imbedded with lava flows.
ex: mt. st Helens and mt. Edna
