Volcanic Landforms

Processes and Hazards

Volcanic Landforms

1. Intrusive Igneous Forms

2. Extrusive – Basalt Landforms

3. Extrusive – Composite volcanoes

4. Extrusive – Rhyolite landforms

1. Intrusive Igneous FormsMagma 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 NamibiaIntrusive igneous rocks are often more

resistant to erosion, so they are topographic highs

Plutons (individual magma chambers)

Batholiths (merged magma chambers)

Laccolith (bubble up strata)

Dikes – vertical magma cutting through

Sill – horizontal magma inserted between

Large

Small

Dike, Spanish Peaks, Colorado

more resistant than surrounding sediment,

so stand out

Dike, Picture Gorge

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)

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.

Volcanic Neck.

Dike

Classroom Resource

Tse bi Dahi

Rock With Wings

Shiprock

Volcanic

Neck

Viscosity Organization

Extrusive – Basalt Landforms

Extrusive – Composite volcanoes

Extrusive – Rhyolite landforms

More Viscous = More Explosive

Classroom Resource

2. Extrusive – Basalt Landforms

• 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 ResourcesRecent Hawaii Eruptions (NPS)

A year of pahoehoe Spatter Cone

Low viscosity releases trapped gases easily, so not explosive.

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

Cinder Cones

SP Crater, AZ

Cinder drops out (like hour glass)

Cinder Cone Developing

Largest drop out first

Largest Clasts: Volcanic Bombs

Classroom Resource

Cinder Cone 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

Sit above Subduction ZonesFuji 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/visualization/collections/volcano.html

Classroom ResourcesNuee Ardente (also called glowing

avalanche, pyroclastic flow)

Set to music (www.mvo.ms)

Soufriere, Montserrat

Nuee Ardente (Glowing Avalanche or pyroclastic flow)

Pompeii, Italy

Mt. Vesuvius

Volcanic Ash

Debris Avalanche

Mt St. Helens Before Eruption

Classroom ResourceLahaar, 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

Arizona has San

Francisco Peaks & Mt Baldy

Classroom Resource

San Francisco Peaks (made by Simpkin, ASU)

4. Extrusive – Rhyolite LandformsSmall 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 ResourcesAfter 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

Imagery seen in this presentation is courtesy of Ron Dorn and other ASU colleagues, students and colleagues in other academic departments, individual illustrations in scholarly journals such as Science and Nature, scholarly societies such as the Association of American Geographers, city, state governments, other countries government websites and U.S. government agencies such as NASA, USGS, NRCS, Library of Congress, U.S. Fish and Wildlife Service USAID and NOAA.c