Adam C. Simon Ph.D., University of Maryland, 2003 Research Associate Department of Geology

1. Adam C. Simon Ph.D., University of Maryland, 2003 Research Associate Department of Geology University of Maryland College Park, MD 20742 p: 301 405 0235 f: 301 314 9661 e-mail: asimon@geol.umd.edu

2. Volcanoes affect our lives in many ways. Today we talk about their construction. Volcanism Eruption of Mt. Etna in Sicily sends a plume of ash visible from space.

3. Planetary Volcanism As we have seen, volcanic activity, or volcanism, is an important factor in shaping other worlds in our solar system. Olympus Mons, Mars Io, moon of Jupiter

4. PERIDOTITE Igneous Rock Classification increasing viscosity increasing melting temperature

5. When magma reaches the Earth’s surface, we call it lava. Aside from lava, volcanoes may eject a variety of common products: -- volcanic gases -- pyroclastic debris Volcanic Products

6. Much more gas can be dissolved in a liquid at high pressure than at low pressure. Liquids that are rich in gaseous components will tend to degas (lose their gas component) as they decompress. Here on Earth, decompression occurs as magma travels from deep sources to shallow regions (like the surface). Volcanic Gases

7. Gas leaving decompressing magma may not be successfully escape. Gas trapped in rapidly-cooling lava forms vesicles, or void spaces in the rock. Extreme examples of vesicular rocks are pumice and scoria: these frothy rocks are lightweight, since most of their volume is air, not rock. Gas-Related Textures vesicular basalt pumice

8. All of the solids ejected from a volcano is collectively called pyroclasts or pyroclastic debris. Pyroclastics The smallest pyroclastic material is ash. Realize that volcanic ash is silicate (glass), unlike ash from burning wood. Pebble-size bits of quenched lava and ash are called lapilli.

9. “Fire fountaining” (as shown here from the 1969 eruption of Mauna Ulu, Hawaii) produces abundant pyroclastic material, including tiny glass beads (Pele’s tears). Pyroclastics

10. Larger chunks of lava, from grape size up to practically car size, are called bombs. Note that on impact these do not explode in flaming carnage, as seen in certain extremely-unrealistic Hollywood productions. Pyroclastics

11. Pyroclastic materials can form their own rocks, with hybrid volcanic and sedimentary components. A tuff is a rock formed from pyroclastic debris. Welded tuffs are hard rocks, which form when pyroclastic material is still very hot when it accumulates on the surface. Molten components cause pyroclasts to ‘weld’ together. Poorly-welded tuffs form from airfall material far from the volcanic source. They carry little thermal energy, since they cool during long travel in the atmosphere. Volcanic/Sedimentary Rocks

12. Lava Flows Smoothly-oozing, low viscosity basalt flows commonly form ropy structures, called pahoehoe (a Hawaiian word).

13. Lava Flows Basalt lava that has lost much of its gas will be more viscous. This lava will form rough, blocky flows called aa.

14. The type of volcano that forms depends on: viscosity of lava, proportion of lava/ash, lava flux. -- flood basalt -- shield volcano -- cinder cone -- composite volcano (stratovolcano) -- lava dome Volcano Types increasing viscosity increasing violence

15. At various points in Earth history massive basaltic eruptions have taken place, producing what are sometimes called flood basalts, or large igneous provinces. These eruptions have left lasting marks of the Earth’s surface and may have had significant effects on global climate. Large Igneous Provinces Why these massive eruptions occur is poorly understood, but they are fundamentally like hot spot Columbia River Ontong-Java plateau Deccan Traps activity on Hawaii, except that much greater volumes are involved and eruptions last for much shorter time periods.

16. Columbia River Flood Basalts This is the largest large igneous province in North America.

17. Deccan Traps, India Flood Basalts 512,000 cubic km of lava (Mt. St. Helens erupted ~1 km3). The eruption about 65 Myr ago is strangely coincident with a global extinction event (i.e., dinosaurs).

18. Shield Volcano Mauna Kea on Hawaii is 10.2 km above the seafloor: the highest mountain on Earth (Everest is only 9.2 km high!). -- low silica, basaltic lava: low viscosity, flows readily -- gentle slope -- non-explosive (in general)

19. -- low to moderate silica lava -- steep slopes, generally symmetrical -- dominantly pyroclastic material Cinder Cones Fernandina, Galapagos, 1991 Cerro Negro, Nicaragua, 1968

20. -- moderate to high silica lava: high viscosity -- steep slopes, generally symmetrical -- layered lava flows and pyroclastic material -- explosive! Composite Volcanoes(stratovolcanoes) Fujiyama, Japan Mayon, Philippines

21. Volcanic Landscapes This satellite image shows how volcanoes can dominate the landscape in some areas. The large ones are stratovolcanoes. Kluchevskoi volcano, Kamchatka, Russia

22. Wilson Butte, CA Domes Panum Crater, CA Lava domes are usually small features, constructed of lava flows of high viscosity. Many volcanoes return to life after hiatuses and form resurgent domes. Novarupta, Alaska

23. Phreatic Eruptions A phreatic eruption is one that is triggered or aided by groundwater or surface water. When this water infiltrates the hot volcanic system, it converts to steam, thus expanding, leading to explosive circumstances. The 1883 eruption of Krakatoa in Indonesia was a famous phreatic eruption. How to make a volcano more destructive than it is on its own? Just add water!

24. Plinian Eruptions In 79 AD Pliny the Younger carefully noted the destructive eruption of Vesuvius in Italy (which, among other things, destroyed Pompeii and Herculaneum, and killed Pliny the Elder). Violent, ash-rich eruptions have since become known as plinian eruptions.

25. Comparison of Scales

26. Diatremes Features such as Ship Rock (NM) and Devil’s Tower (WY) are diatremes: the eroded remains of extinct volcanoes.

27. Extinct Volcanoes In spite of their volcano-esque shapes, they actually are part of the volcanic conduit that was underground when the volcano was active.

28. Airfall Distribution 6850 yr ago, Mt. Mazama, OR, erupted, sending a recognizable layer of ash throughout the northwest. We now know this volcano as Crater Lake.

29. Big Pyroclastic Eruptions of North America This illustration shows the Bishop Tuff, which was deposited 760,000 yr ago, the most widespread ash layer of the last hundred million years in North America.

30. The Bishop Tuff This eruption scatter ash hundreds of kilometers away, and the area close to the eruption was treated to a thick blanket of hot ash!

31. Ash Layers Distant deposition of volcanic material is important to dating sedimentary rocks, as we will see next class. ash layers 10-100,000 yr old lake sediments at Mono Lake, CA, showing several distinct, regionally-recognized ash layers.

32. There are three particularly good choices for which area will have the next big volcanic eruption in the continental US. Waiting for the Big One Area one is the Pacific Northwest, from northern CA into BC. Continued oblique subduction sustains lava supply at depth. Let’s not forget what happened in 1980.

33. The second choice is Long Valley, CA. This was the source of the Bishop Tuff and has seen cinder cone construction as recent as ~250 years ago. The Next ‘Big One’? caldera north

34. Long Valley in Cross-Section This interpretation was produced by examining surface geology, deep drill holes, and seismic data.

35. The Next ‘Big One’? Choice three is Yellowstone, WY. This caldera has blasted out gigantic pyroclastic eruptions in the last couple million years. (honorable mention: Valles caldera, NM) We will talk about the implications of volcanic eruptions for society later in class.

36. Credits Some images in this presentation come from: Plummer, McGeary and Carlson, Physical Geology, 8th ed.; NMNH, Global Volcanism Project; Geological Society of America (Geology); USGS; Hamblin and Christiansen, Earth’s Dynamic Systems, 8/e; D Swanson, USGS; EOS; Univ. of North Dakota’s Volcano World