Volcanic Landforms
Processes and Hazards
Volcanic Landforms
1.
2.
3.
4.
Intrusive Igneous Forms
Extrusive – Basalt Landforms
Extrusive – Composite volcanoes
Extrusive – Rhyolite landforms
1. Intrusive Igneous Forms
Magma solidified at great depth (so mineral
sizes are large)
Plutons (individual magma chambers)
Batholiths (merged magma chambers)
Pluton seen because of glacial erosion, Chile
Brandberg, Western Namibia
Intrusive igneous rocks are often more
resistant to erosion, so they are
topographic highs
Plutons (individual magma chambers)
Large
Batholiths (merged magma chambers)
Laccolith
(bubble up strata)
Small Dikes – vertical magma cutting through
Sill – horizontal magma inserted between
Dike, Spanish Peaks, Colorado
more resistant than surrounding sediment,
so stand out
Dike, Picture Gorge
Volcanic Neck.
Dike
Over time, the less resistant rock
(i.e., pyroclasts and less
consolidated lava flows) comprising
the flank of the volcano is eroded
away leaving the resistant neck
exposed in relief.
Shiprock (Tse bi Dahi, Rock With Wings), New Mexico is the classic example of a
volcanic neck (base of composite volcano, so deep that is intrusive rock)
Classroom Resource
Tse bi Dahi
“Rock With Wings”
Shiprock
Volcanic Neck
2. Extrusive – Basalt Landforms
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Basalt Flow
Flood Basalts
Cinder Cone
Shield Volcano
Shield & Cinder Cone – from basalt
eruptions
Later: Composite volcano
Basalt flows will travel great distances and slope angles will
reflect low viscosity.
Classroom Resources
Recent Hawaii Eruptions (NPS)
A year of pahoehoe
Spatter Cone
Classroom Resources
Etna Tourist Office
No Lives Lost
Different Textures, Same Basalt
Rock
Pahoehoe
a’a
Lava Tubes – so fluid that inside
keeps moving & creates caves
Classroom Resource
Lava tube breakout
Lava Tube, Hawaii
near Flagstaff, AZ
Mt St. Helens, OR
Buries old
topography
Flood Basalt, Southern Utah
Flood Basalt
Flood Basalt, Oregon
Cinder Cones
SP Crater, AZ
Cinder drops out (like hour glass)
Cinder Cone Developing
Largest drop out first
Classroom Resource
Cinder Cone Bombs
Largest Clasts:
Volcanic Bombs
Crater: depression at top formed by
force of eruption
Owens Valley, Calif
Very common in Arizona:
especially S.F. Volcanic Field
Sunset Crater, AZ
Shield
Volcanoes
Isabela Island,
Galapagos
Hawaii built
from Shield
Volcanoes
Weight of new lava has depressed
the crust around Hawai’i
Moat
~ 5000 m
Below
Sea
Level
Mauna Loa: note gentle
profile from fluid basalt flows
Mauna Kea
Often have Summit Caldera –
from collapse as lava flows away
3. Extrusive – Composite Volcanoes
Mt Ararat, Armenia
Composite Volcano, Oregon
Sit above Subduction Zones
Fuji
Egmont
Extraordinarily Dangerous
from Nova
from Nova
from Nova
Future Disaster: Popocatepetl,
next to Mexico City & Puebla
Composite
Volcano
Online Animations
Volcanic Hazards
http://serc.carleton.edu/NAGTWorkshops/vis
ualization/collections/volcano.html
Classroom Resources
Nuee Ardente (also called glowing
avalanche, pyroclastic flow)
Set to music (www.mvo.ms)
Soufriere, Montserrat
Nuee Ardente (Glowing Avalanche or
pyroclastic flow)
Mt. Vesuvius
Pompeii, Italy
Volcanic
Ash
Debris Avalanche
Mt St. Helens Before Eruption
Classroom Resource
Lahaar, Mt St. Helens
Fly Over
Mt Mazama (could be Rainier)
Caldera – from collapse after lava has
“evacuated” from magma chamber
Crater Lake
Mt Hood (my bet to go next)
Mount Pinatubo
Classroom Resources
Colorado
has no
active
volcanoes!
4. Extrusive – Rhyolite Landforms
Small Eruptions: Rhyolite Domes, Mt Elden
Rhyolite so
viscous
has trouble
flowing, so
piles up in
dome
shape
Many Rhyolite Domes near
Mono Lake, Calif
Mammoth Lakes, still active
evidence: carbon dioxide
Classroom Resources
After major eruption of composite volcano,
will often start to rebuild with rhyolite
domes
Arizona has many rhyolite caldera
super eruptions (17-27 myr ago)
Superstition Mtns
Chiricahua Mtns
Toba – almost did us in