A presentation on the volcanic history and future of Yellowstone, designed for an introductory college course on volcanology.

1. Volcanism at
Yellowstone
Presentation by Tara K.
Blalock

2. 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

3. Geography of
Yellowstone
A ppr
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760 m
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Image taken from Google

4. Geography of
Yellowstone
Approximate path of
Yellowstone volcanism
Image taken from Google

5. Geography of
Yellowstone
- 100 eruptions over
16.5 million years
- 7 historic calderas
Image from Smith et. al.

6. Geography of
Yellowstone
Image taken from Google

7. Geography of
Yellowstone
Sour Creek
“resurgent dome”
Mallard Lake
“resurgent dome”
Image from Wicks, et. al.

8. The Yellowstone Hotspot
Traditional Hotspot Theory:
A mantle “plume” originating at the core-mantle boundary
facilitates upward melting and volcanism at the surface
Continental Crust
Lithospheric Mantle
Mantle
Outer Core

9. The Yellowstone Hotspot
Newer 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
Upper Crust
Lower Crust
25 mi
Lithosphere
50 mi
75 mi
100 mi
Upper Aesthenosphere
U U U U

10. 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 boundary
3.“Yellowstone” phase: rhyolitic explosive
eruptions and flows
4.“Snake River Plain” phase: basaltic flows

11. Phase 1: “Pre-Yellowstone”
Phase
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 Crust
Lower Crust
25 mi
Lithosphere
50 mi
75 mi
100 mi
Upper Asthenosphere
U U U U

12. Phase 2: “Yellowstone” Phase
- 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.
Upper Crust
Lower Crust
Lithosphere

13. 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 eruptions
Rhyolite flow: post-caldera

14. 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.

15. Volcanic Deposit
Dark = primarily magnetite and pyroxine
Light = large pieces mostly crystalized
pumice; smaller are pumice, feldspar
and quartz
Tuff Cliff: Image from USGS Bulletin 1347
Tuff Deposit: Image from USGS Bulletin 1347

16. Volcanic Deposit
Rhyolite flow
Image from USGS Bulletin 1347

17. Volcanic Deposit
Image from Fool-On-The-Hill
Image from USGS Bulletin 1347
Black = obsidian
Light = feldspar and
quartz
Image from USGS Bulletin 1347

18. Volcanic Deposit
Basalt flows!
Columnar jointing
Image from Ellenm1
Image from Piedmont Fossil

19. Hydrothermal Processes
Angel Terrace
Thermal Pool,
Lower Geyser
Basin
Image from Kris Taeleman
Image from AR Nature Gal
Clepsydra Geyser
Thumb Paint Pots
Image from ZaNiaC
Image from Serene Silence

20. Hydrothermal Processes
Image from USGS Bulletin 1347

21. Future Volcanism at
Yellowstone
A breathing landscape?
Image from Wicks, et. al.

22. Future Volcanism at
Yellowstone seismicity?
Increased
Image from USGS, 2009

23. Future Volcanism at
Yellowstone
Changes in hydrothermal activity?
Old Faithful
Image from Kris Taeleman

24. 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

25. Image from Human Nature