Transcript Ch 10 Volcanism Class Notes_Part_3_2014

LIFE CYCLE OF VOLCANOES
ACTIVE VOLCANO
• Erupting now
• Has erupted in the recent past
• Shows signs of erupting in the near
future
DORMANT VOLCANO
• Volcano that has not erupted recently
• But has in recorded history
• It is expected to erupt again
EXTINCT VOLCANO
• Has not erupted in recorded history
• Is not expected to erupt again
VOLCANISM UNDERGROUND
(SUBTERRANEAN)
IGNEOUS INTRUSIONS
• Flows of magma that cool and harden
before they reach the surface
• Intrusive rocks have a large grain or
crystal size
• The deeper the intrusion, the larger the
crystal
VOLCANIC NECK
• Intrusive structure composed of
cooled magma trapped in the vent or
throat of a volcano
DEVIL’S TOWER, WY
STEAMBOAT SPRINGS, CO
SHIP ROCK, NM
DIKE
• A tabular, mostly vertical intrusion
• Vertical structures are called “DISCORDANT” in
geology
• Depth of intrusion determines the grain size
• Dikes are often more resistant to erosion than
surrounding rock; leave a dam-like structure on
surface
• There are ancient dikes in Wisconsin
SHIP ROCK, NM Dike
DIKE IN ALASKA
SILL
• Relatively horizontal structure that is parallel
to rock layers
• Parallel w/ layers is called “CONCORDANT”
in geology
• Magma squeezes between layers and
solidifies into a sill
• Grain size is dependent on depth it is formed
PURCELL SILL, MONTANA
Limestone
Sill
Diorite
Limestone
LACCOLITH
• Close relative of the sill; concordant pluton
• Slight dome or mushroom shape- middle
thicker than sides
• Often leaves a bulge at the surface
• Can form smaller dome mountains
LACCOLITH BEFORE & AFTER EROSION
Laccolith
Sills
PLUTON (MAGMA CHAMBER)
• Igneous body that has cooled and crystallized
beneath the surface
• Plutons typically have irregular shapes
• Can cause doming at the surface
STOCK
• Small, discordant pluton
• Outcrop area of less than 100 km2
BATHOLITH
• Large discordant pluton
• Outcrop area is greater than 100 km2
• Most are granitic or felsic in
composition
VOLCANISM UNDERGROUND
(SUBTERRANEAN VOLCANISM
STRUCTURES YOU SHOULD
KNOW
STRUCTURES YOU SHOULD
KNOW
ANOTHER GRAPHIC OF
INTRUSIONS