Volcanism at YellowstonePresentation by Tara K.

Blalock

Presentation Objectives:

• Become familiar with the geography of Yellowstone

• Explore Yellowstone hotspot theory• Introduce 3 phases of Yellowstone volcanism• Dissect geology of Yellowstone volcanic

deposit• Interpret Yellowstone hydrothermal processes• Predict future volcanic activity at Yellowstone

Approximately 1760 mi from

here!

Geography of Yellowstone

Image taken from Google Earth

Geography of Yellowstone

Image taken from Google Earth

Approximate path of Yellowstone volcanism

Geography of Yellowstone

Image from Smith et. al.

- 100 eruptions over 16.5 million years

- 7 historic calderas

Geography of Yellowstone

Image taken from Google Earth

Geography of Yellowstone

Image from Wicks, et. al.

Mallard Lake “resurgent dome”

Sour Creek “resurgent dome”

The Yellowstone Hotspot

Outer Core

Mantle

Lithospheric MantleContinental Crust

Traditional Hotspot Theory:A mantle “plume” originating at the core-mantle boundaryfacilitates upward melting and volcanism at the surface

The Yellowstone HotspotNewer Yellowstone Hotspot Theory: - Radioactive decay and decompression melting within the asthenospheric mantle at only 125 miles depth provides the hotspot origin - Sheering at the lithospheric boundary causes a 300-mile magma pool - Basalt melt “blobs” from the mantle melt granitic crustal rock

25 mi

50 mi

75 mi

100 miU U U U Upper Aesthenosphere

LithosphereLower Crust

Upper Crust

3 Eruption Phases

Using seismic tomography on the Snake River Plain, 3 eruption phases have been determined for the Yellowstone hotspot:2.“Pre-Yellowstone” phase: basaltic pooling at the mantle-lithosphere boundary3.“Yellowstone” phase: rhyolitic explosive eruptions and flows4.“Snake River Plain” phase: basaltic flows

Phase 1: “Pre-Yellowstone” Phase

25 mi

50 mi

75 mi

100 miU U U U

Rising basaltic magma from 125 miles within the asthenospheric mantle pools at the base of the lithosphere, and produces a topographic “bulge” on the surface approximately 300 miles in width

300 miles

Upper Asthenosphere

Lithosphere

Lower Crust

Upper Crust

Phase 2: “Yellowstone” Phase

Upper Crust

Lower Crust

Lithosphere

- The “supervolcano” phase…basaltic magma rises and melts the lower crust, producing a silica-rich magma chamber. - Rising magma bulges the surface, which causes faulting and earthquakes in a ring around the chamber. - Faults that reach the magma chamber cause rapid decompression within, which allows volatiles to expand at supersonic speeds and rhyolitic lava to erupt.- A catastrophically explosive eruption forms a massive caldera.

The current Yellowstone caldera is 28 miles by 45 miles.

Phase 2: “Yellowstone” Phase

- Post-caldera eruptions - rhyolite flows - eventually fill the caldera.- Yellowstone’s last post-caldera rhyolite eruption was 70,000 years ago. Rhyolite tuff: a single cooling

unit formed during caldera-forming eruptionsRhyolite flow: post-

caldera

Phase 3: “Snake River Plain” Phase

- Without the hotspot, the silica-rich magma within the chamber cools more quickly than the silica-poor basaltic magma, allowing the basalt to erupt.- It levels the landscape and helps the elevation to subside.

Volcanic Deposit

Tuff Cliff: Image from USGS Bulletin 1347

Tuff Deposit: Image from USGS Bulletin 1347

Dark = primarily magnetite and pyroxine

Light = large pieces mostly crystalized pumice; smaller are pumice, feldspar and quartz

Volcanic Deposit

Image from USGS Bulletin 1347

Rhyolite flow

Volcanic Deposit

Image from Fool-On-The-Hill

Image from USGS Bulletin 1347

Image from USGS Bulletin 1347

Black = obsidian

Light = feldspar and quartz

Volcanic Deposit

Image from Ellenm1

Image from Piedmont Fossil

Basalt flows!

Columnar jointing

Hydrothermal Processes

Image from Kris Taeleman

Image from AR Nature Gal

Image from ZaNiaCImage from Serene Silence

Thumb Paint Pots

Clepsydra Geyser

Angel Terrace

Thermal Pool,Lower Geyser Basin

Hydrothermal Processes

Image from USGS Bulletin 1347

Future Volcanism at YellowstoneA breathing landscape?

Image from Wicks, et. al.

Future Volcanism at Yellowstone

Image from USGS, 2009

Increased seismicity?

Future Volcanism at YellowstoneChanges in hydrothermal activity?

Image from Kris Taeleman

Old Faithful

Conclusions

•Evidence shows it is likely that Yellowstone will erupt again, although the magnitude of the eruption is uncertain

•Close monitoring of uplift and subsidence, seismic and hydrothermal data will likely indicate future volcanic activity

Image from Human Nature