Midterm Exam Grade Spread

1. Midterm Exam Grade Spread Please see me

2. Monday, 28 January, 2013 Presentations Sakurajima, Japan Monica Li Elise Ozarowski Reventador, Ecuador Sonja Sepkowitz Nick Manning Navidad, Chile Madeline Kurtz Fritha Wright Surtsey, Iceland Naimat Merzaiee Chen Li Mt. Erebus, Antarctica Beth Fleming Christine Francis Karthala, Grand Comoro Island Anthony Shimamoto Galeras, Colombia Sam Fresher Phillip Swindells Merapi, Indonesia Brendan McNeill Ellie Oakford Stromboli, Italy Kaitlin Curran Emily Nelson Changbaishan, China-Korea border Wei Ma Tashi Palmo

3. Tuesday, 29 January, 2013 Presentations Piton de la Fournaise, Réunion Island Papa Loum Joey Barnes Erta Ale, Ethiopia Alicia Fawcett Patrick Martin Taal, Philippines Kate Dong Shama Ramos Popocatepetl, Mexico Billy Polk Alex Rutan Mt. Kilimanjaro, Tanzania Tyler Will Nils Martin Nyiragongo, Dem. Republic of Congo Leah Breen Catherine Kapples Fuego, Guatemala Lils Liang Rosie Melendez Karymsky, Kamchatka, Russia Drew Choos Teddy Echeverria Tofua, Tonga Mikaela Johnson Emily Malinowski Cleveland, Aleutian Islands Bip Collery Laura Tierney

4. HOT NEWS! While WE were taking our exam last week, Sicily's Mt. Etna was undergoing another eruption!

5. EXPLOSIVE ERUPTIONS and Pyroclastic Flows Part II

6. As you'll see in the Pinatubo video, RADIOCARBON DATING of organic matter buried by volcanic deposits is often the best way to determine age estimates for past eruptions. (Radiocarbon Dating, or 14C dating, works only on organic matter, and is useful on materials generally up to around 40,000 years of age - hardly applicable to rocks but very useful for any organic matter that may be associated with a geologic unit, like a volcanic ash (at right).

7. THE MAIN REASONgeologists would want to know about when a volcano had erupted is because that can often be the best indication of when it might erupt again. Here's an hypothetical example: 14C dating indicates that Mount Whunkatunka has erupted: 285 years ago (corroborated by historical records) 550 years ago 800 years ago 1050 years ago 1175 years ago 1350 years ago and 1600 years ago You have a chance to buy some beautiful lakeside property at the foot of the mountain, for a bargain price. Do you think this would be a wise investment on your part? Why or why not? And how do you find OUT the eruptive history of this volcano?? How do you know it's a volcano in the first place??

8. Ceboruco, Mexico Sutter Buttes, California 1875 1.5 My ago Seward Peninsula, Alaska – landslides in limestone High Sierra Nevada – non-volcanic (apparent dome is a glacier)

9. Here are the kickers: (1) We only know the precise eruptive histories of a relatively small handful of volcanoes! (2) Figuring this out can take years of work. The need is particularly great in those areas where populations are great but economies are weak. (3) FACT: Over 40% of the world's human population lives within striking distance of volcanoes - on the Pacific Ring of Fire in particular, but also including the Mediterranean and Africa.

10. Even the big volcanoes are minor compared to THE great eruptions of the past several million years.

11. These MAJOR CALDERA eruptions fortunately are rare events! (~ once every 100,000 years worldwide) Some notable ones would include: Toba 70,000 years ago Yellowstone 600,000 years ago Long Valley, CA* 780,000 years ago Ngorongoro Caldera, Tanzania (?) ~1,000,000 years ago Valles Caldera, NM 1,100,000 years ago Yellowstone 1,200,000 years ago Valles Caldera, NM 1,400,000 years ago Yellowstone 2,200,000 years ago * In 1980-82, hundreds of earthquakes per day recorded movement of magma deep beneath Long Valley, but activity since then has been relatively quiet most of the time. Note that the calderas produced in these enormous explosive events are commonly TENS OF KM across! The ashes that are produced also become important stratigraphic markers in the geology. See http://www.extremescience.com/zoom/index.php/volcanoes/24-caldera-volcano

12. VEI = Volcano Explosivity Index Yellowstone Caldera 2.5 million years ago (~ 6000 km3)

16. Mono Lake Mono Craters Mammoth Mountain Ski Resort Long Valley Caldera, eastern Sierra Nevada, California

17. How do these come about? Here's one scenario, worked out for the Long Valley Caldera, applicable to Yellowstone and probably the others as well. We'll start with a relatively calm landscape (ignoring the possibility of previous eruptions to help simplify matters!).

18. Mafic magma, commonly from a mantle plume, begins to rise beneath the area, melting the higher-silica rocks ahead of it to produce a secondary magma of felsic composition.

19. As this plume rises, because the mafic magma is much hotter, it melts an increasing amount of the higher-silica rocks ahead of it. (Remember that the higher the silica content, the lower the melting temperature.) The overlying crustal rocks also probably have significant water in them, which also will lower their melting temperatures.

20. A large plume of felsic magma is generated ahead of the rising mafic plume, which slows as it is starting to crystallize itself from the lower temperatures. (It's been losing a tremendous amount of heat in melting all of the surrounding rocks, and also has a much higher crystallization temperature.)

21. Stress created by the rising magma creates both earthquakes and fractures in the Earth's surface, from which volcanic gasses start to escape. Air samples taken from soils in Long Valley ca. 1996, in an area where all the trees had died, showed CO2 levels of approximately 90%. Normal air is <0.03% carbon dioxide.

23. Not uncommonly, the magmas never make it to the surface, but instead crystallize underground in a layered pluton. Gases may continue escaping for thousands of years, and hot spring activity is also common if water is available.

24. The more extreme result is a catastrophic eruption that opens a hole in the Earth up to 5000 km2 in size, in an eruption that begins small, by "unzipping" as multiple vents erupt simultaneously. The overall area may then remain an area of tectonic, thermal and renewed volcanic activity for centuries or even millennia.

25. Mammoth Mountain ski area

27. At left, a specimen of Bishop Tuff erupted from Long Valley Caldera some 760,000 years ago. In places, this unit is over 60 m (200 feet) thick.

28. The Yellowstone Caldera is also something worth considering. The park itself is about the size of the state of Rhode Island. By some estimates, this caldera may have yielded the largest explosive eruption in Earth history in many millions of years.

29. The mountains in the distance are the far rim of the Yellowstone Caldera. The opposite rim is almost an equal distance BEHIND this point of view. Yellowstone Lake lies in the foreground.

30. The Yellowstone Hot Spot MAY be the same as that which was responsible for the Columbia flood basalts.

32. Yellowstone experienced over 1000 earthquakes early in 2010, but ... fortunately, nothing happened!

33. The "breathing caldera" analogy ....

35. The Pearlette Ash (as it's called) from Yellowstone is still quite thick in central Kansas! (Kansas Geological Survey photos)

36. Tomorrow: SUPERVOLCANO!