Download Volcanoes

Results of plate
tectonics:
1.volcanism
2.diastrophism
3.earthquakes
Volcanism
Volcanism

movement of molten rock from earth’s
interior through a conduit or opening
to, or near, the surface
Types of volcanism:
A. Extrusive
1. Volcanoes
 a) shield
 b) composite
 c) cinder cone
2. Lava Flows
 flood basalts
B. Intrusive
A. Extrusive Volcanism

Magma reaches the surface (lava) and
cools above the surface.
1. Volcanoes: hills or mountains of
volcanic material that was released
under pressure from a vent
– >500 active (4/5 “ Ring of Fire”)
- subduction, rift valleys, mid-oceanic ridges,
hot spots
Types of Volcanoes:
a) Shield Volcanoes
– broad, gently sloping surfaces
 examples: Hawaii, Azores, Mt. Hekla in Iceland
– tallest mountains on earth are shield
volcanoes from the ocean floor
– effusive eruption
 nonviolent eruption due to type of magma
– low viscosity; 2200 degrees F, little gas in magma
– Iron, magnesium, low in silica: from asthenosphere
 Primarily basalt
b) Composite Volcanoes
– steep-sided
– alternating layers of pyroclastics and lava
 pyroclastics: rock pieces ejected:
– Tephra: pulverized rock
– Scoria: cindery vesicular rock
– ash falls and lava flows
– subduction zones
 examples: Mt. St. Helens, Mt. Rainier, Mt. Fuji,
Mt. Hood
– explosive eruption due to type of magma
 higher viscosity, 1600 F; contains gases
 from melting of lithosphere: more silica
Types of volcanism:
A. Extrusive
1. Volcanoes
 a) shield
 b) composite
 c) cinder cone
2. Lava Flows
 flood basalts
B. Intrusive

Composite = stratovolcano
Insert map of volcanoes

CALDERA: landform associated with some
composite volcanoes
– large bowl-shaped depression left after a
composite volcano blows; mountain collapses
inward
– Example: Crater Lake

c) Cinder Cones
– steep, cone-shaped hills of pyroclastics
– moderately explosive
– most abundant and smallest (<1500 ft.
high)
– central crater
– form rapidly, erode rapidly
 example: central Arizona; Paricutin, Mexico;
Idaho Snake River Plain
Types of volcanism:
A. Extrusive
1. Volcanoes
 a) shield
 b) composite
 c) cinder cone
2. Lava Flows
 flood basalts
B. Intrusive
2. Lava Flows
Effusive (nonviolent) eruptions
 spreading boundaries and hot spots
 lava spreads out over surface; coming out of
fissure (rift)

– example: Lake Superior shore
 1.2 billion yrs BP

can accumulate layer upon layer : FLOOD
BASALT
– examples: Columbia Plateau (Washington), Deccan
Plateau (India)
B. Intrusive Volcanism

Magma solidifies beneath surface; intrudes
into cracks in crust
– intrusions can later be exposed at surface;
more resistant than surrounding rock
Intrusive landforms

Neck: narrow steep-sided peak , formed
in central vent of an extinct volcano
– E.g., Ship Rock, Devil’s Tower
Dike: thin layer of igneous rock ;
vertical; cuts across other rock layers
 Sill: thin layer of igneous rock between
rock layers
 Plutons: large igneous bodies at depth

– batholiths
– laccolith: dome-shaped