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Guest Thinkers —

GSA 2009 Wrap Up – Part 1

Some notes from the GSA 2009 meeting, including the size of Toba, the latest on the history of South Sister, the explosive life of central Oregon scoria cones and the kimberlites of New York.

I finally remembered to bring my GSA notes with me to the office, so I can finally post a wrap up of what I saw/heard at the big 2009 meeting in Portland. I’ll have a specific post on Kasatochi – too much to say here. However, a great time was had by all!


The crater of Collier Cone in Oregon. The scoria cone likely experienced years of explosive strombolian eruptions when it formed.

Some interesting volcano-related notes:

  • Clive Oppenheimer pointed out that the Toba eruption 74,000 years ago covered >1% of the Earth’s surface with >10 cm (~4 in) ash. To put that in perspective, the Earth is ~196,940,400 square miles / 504,167,000 km2, so Toba blanketed almost 200,000 square miles / 500,000 km2 with more than 10 cm ash – and 10 cm is enough to cause significant havoc to plants, breathing and water.
  • I was personally excited to hear that South Sister in Oregon has erupted a lot of rhyolite/rhyodacite over its history – including Rock Mesa and Devil’s Hills. Judy Feirstein from the USGS said that these silicic magmas are common throughout the activity of the volcano, which peaked from 20,000-40,000 years ago.
  • Also on the South Sister front, it appears that any uplift that was happening on the volcano has ended. The west slope of the volcano was noticed to be very slightly bulging back in 2001 – adding up to a grand total of ~4.6 x 107 m3 – or roughly 3-5 cm uplift. However, most geophysical models for the uplift suggest that there is no mass flux towards the surface, so the likelihood of any eruption from this event is very low.
  • If you’ve ever been up on Mackenzie Pass in the Central Oregon Cascades, you’ve seen a lot of the young (Collier, Yapoah and 4-in-1 in specific) experienced explosive eruptions – specifically strombolian eruptions. They determined this by looking at the tephra deposits near the vents and compared them to the record at Paricutin in Mexico. These Oregon scoria cones likely experienced years of explosive eruptions if the deposits are any indication.
  • Finally, did you know that kimberlites litter the eastern U.S.? There are kimberlites in middle New York, western Pennsylvania, North Carolina and more. Likely they are caused by reactivation of structural features related to the various orogenies that east coast has experienced, but I had no idea.
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