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 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) 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 Resources Recent 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 Zones Fuji Egmont

Extraordinarily Dangerous from Nova

Future Disaster: Popocatepetl, next to Mexico City & Puebla

Composite Volcano

Online Animations Volcanic Hazards ualization/collections/volcano.html

Classroom Resources Nuee Ardente (also called glowing avalanche, pyroclastic flow) Set to music ( Soufriere, Montserrat

Nuee Ardente (Glowing Avalanche or pyroclastic flow)

Pompeii, Italy Mt. Vesuvius

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

Arizona has San Francisco Peaks & Mt Baldy

Classroom Resource San Francisco Peaks (made by Simpkin, ASU)

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

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