Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: chris on 23/12/2009 00:32:33
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Scientists claim that there is a "supervolcano" beneath Yellowstone. What is the evidence for this, why did it form and what are the likely consequences?
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The evidence for a 'supervolcano' at Yellowstone is the three previous Volcano Explosive Index 8 (VEI 8) eruptions, and their resulting calderas, that have occurred there.
There appears to be a long-lived 'hotspot' beneath Yellowstone, as there is at Hawaii, and just as with Hawaii, you can trace the movement of the tectonic plate over the stationary hotspot from the trail of previous eruptions.
There will almost certainly be further eruptions at Yellowstone, but they are more likely to be local < VEI8 events. However, another VEI8 eruption is certainly possible, given Yellowstone's previous history. A VEI8 eruption from anywhere on Earth would have global consequences.
Have a look at the USGS Yellowstone Volcano Observatory (YVO) website at:
http://volcanoes.usgs.gov/yvo/ (http://volcanoes.usgs.gov/yvo/)
The FAQ there at:
http://volcanoes.usgs.gov/yvo/about/faq/index.php (http://volcanoes.usgs.gov/yvo/about/faq/index.php)
will answer most questions. I thoroughly recommend watching the three vid interviews with Jake Lowenstern, the Scientist-in-charge at the YVO, that are linked to on the home page.
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Bass is the one to address this. Yellowstone geology is his hobby and he presents lectures on the volcano, its origins and its future.
After Christmas I am sure he will bore us all to death with the COMPLETE answers!
Meanwhile, the calderas and the present volcanic activity are the evidence for it's existence, as Lee stated. The progression of the plume and resulting hot-spot that forms the present caldera can be followed all the way back to the Modoc Plateau of Northern California and southern Oregon.
It then gets "overprinted" by the Cascade Volcanic Range along the coast of Californian and Oregon. I have some data that is still proprietary that follows the calderas into this mountain range.
Until Bass returns - http://en.wikipedia.org/wiki/Yellowstone_Caldera
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Heh! - I didn't realise that the hotspot trail could be traced that far away i.e. to the Cascades.
I look forward to hearing what Bass has to say - I'm just an armchair geology enthusiast.
Re the scale of the consequences of these very large eruptions: the Lake Toba eruption of ~74000 years ago, which erupted 2800 km3 of magma, has been estimated to have killed 60% of human life on Earth.
Even larger eruptions have occurred in the distant past. The Deccan Traps eruption, which was contemporary with the Cretaceous–Tertiary extinction event erupted approx 1000000 km3 of magma and the Siberian Traps eruption, which was coincident with the Permian extinction where an estimated 90% of all life on Earth was killed, erupted up to 4000000 km3 of magma.
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Heh! - I didn't realise that the hotspot trail could be traced that far away i.e. to the Cascades.
In fact, not many geoscientists (other than JimBob) have realized this either. The widely accepted inception for Yellowstone in the North American continent is McDermitt Caldera (16 million years old or mid-Miocene)in northern Nevada and southern Oregon.
Even larger eruptions have occurred in the distant past. The Deccan Traps eruption, which was contemporary with the Cretaceous–Tertiary extinction event erupted approx 1000000 km3 of magma and the Siberian Traps eruption, which was coincident with the Permian extinction where an estimated 90% of all life on Earth was killed, erupted up to 4000000 km3 of magma.
A distinction needs to be made between large, explosive, silicic caldera eruptions and volcanic provinces such as the Deccan and Siberian Traps (and other flood basalts). While the Traps can be technically termed "supervolcanos" because of the volume of lava erupted, they were not explosive. Much like Hawaii, these were basalt provinces, their mafic lavas flowing easily to cover the landscape.
The La Garita Caldera (Colorado), which erupted in the early Miocene (around 28 m.y.) was truly enourmous, ejecting over 5,000 km3 of material in an explosive eruption. Large silicic calderas have been recognized throughout the world and throughout geologic time.
How did Yellowstone form? As LeeE and JimBob pointed out, a hotspot exists beneath Yellowstone. Hotspots are areas of long-lived volcanism (millions of years) that originate in the mantle. The evidence is not yet clear as to whether hotspots are caused by deep mantle plumes or are more shallow mantle features. In Yellowstone, hot mantle material rises beneath the continental crust, creating a "bulge" or topographic high and begins to melt the silica-rich continental material. The melted continental material is high viscosity, so it rises slowly through the crust. These silicic magmas (we'll call them rhyolites for the sake of convenience) eventually rise to within a few kilometers of surface. Along the way, due to crystallization, the introduction of groundwater and other factors, volatile compounds begin to build in the magma. The accumulation of volatiles (water, CO2, SO2, etc) in these large, slow-moving magmas probably takes hundreds of thousands of years. At this point, the magma is somewhat similar to can of soda pop (or beer, if you prefer)- full of dissolved volatile compounds (CO2 in the soda or beer) waiting to be shaken up and released. Once the pressure is released (like popping the top on warm beer can), these volatiles flash into gas, further increasing pressure in the system and causing the explosive eruptions, creating immense ash clouds as the rhyolite is erupted along with the expanding gas as tiny particles. This process continues until most of the volatiles are used up- these large eruptions are thought to only last a few days to a week.
The hotspot creates a track, since it is located in the mantle, as the North American tectonic plate slides over the mantle to the southwest. Once the crust passes over the hotspot, it begins to cool, shrink and crack, allowing mantle basalts to erupt and cover the old calderas (Snake River Plain).
What will happen next in the Yellowstone system?
Eventually there will be another massive eruption, likely somewhere northeast of present of caldera. Timing? Probably within the next 50,000 years. The good news is that there are no signs of imminent eruption- I still sleep well even though the Park is only a few hours drive. It is more likely that we will see earthquakes, landslides, steam explosions and possibly even small volcanic eruptions in the next few hundred years.
My research leads me to believe that the next (4th) caldera cycle has already started- which is something I hope to see published in the not too distant future.
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My research leads me to believe that the next (4th) caldera cycle has already started- which is something I hope to see published in the not too distant future.
That's very interesting indeed Bass, and I believe that statement represents quite a large reduction in the degree of uncertainty about Yellowstone, does it not? Please keep us up to date re progress (that's the progress of your paper, not Yellowstone [;)]).
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Here's a recent (2008) article that addresses JimBob's assertion that the Yellowstone hotspot traveled through northern California.
http://www.geol.ucsb.edu/faculty/busby/Manuscript_pdfs/Garrison_et_al_2008.pdf
The authors conclude that the mid-Miocene Lovejoy Basalt probably erupted as a consequence of a fast southwest-moving mantle plume that split from the Yellowstone hotspot- and does not support the Yellowstone hotspot being located under northern California before the eruption of McDermitt Caldera.
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Hmm... A fast moving mantle plume is a new concept to me. I thought that mantle plumes were more or less stationary, and it's the plates that move.
Considering how deep mantle plumes are believed to go, wouldn't it require a disproportionate amount of change throughout the depth of the mantle for the plume to move?
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Maybe "plume head" would be a better term. The Yellowstone plume head is also thought to have caused the Steens Basalts, Columbia River basalts, and lava flows along the northern Nevada rift.
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That's interesting, but if the mobile plume head remains attached to the stationary plume I'd expect it to oscillate around more or less randomly. That is, unless there's not yet been enough time for several oscillations to have occurred and we've only just seen one 'swing'.
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The initial plume head must have been enormous, given the amount of eruptive material in the mid-Miocene (~15 m.y. ago). Mantle material (tholeitic basalts) likely erupted along lines of existing crustal weakness. Similar to the northeast trending track of the Yellowstone hotspot (from McDermitt across the Snake River Plain), there is another time-progressive track of volcanism from McDermitt to the northwest, ending at Newberry Caldera near Bend Oregon. One hypothesis is that crustal extension (from the initial plumehead) caused a local melting anomaly at the mantle-crust boundary, and that this anomaly migrated northwestward in sync with westward crustal extension.
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Aha, so rapidly mobile in the sense of moving along existing weaknesses, or along weaknesses created as a result of the initial eruption?
Heh - when I was spending a lot of time developing aircraft for the FlightGear open-source flight simulator, and when I wasn't actually flight testing them, I'd often go on an aerial tour of the Cascade range volcanoes and was especially impressed with the Newberry caldera (The FlightGear 'terrain' covers the entire world, between 60N and 56S, being derived from the SRTM 3 Arc-sec data, which generally give a good impression of large geological features. Crater Lake was pretty good too, and I was even able to find Barringer Crater, albeit a bit glitchy, and which is not volcanic, of course).
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I can attest to the presence of basalt in this area. My back garden is a gigantic pile of basalt cobbles (no, not cobblers) with next to no dirt in it at all [;D]
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Geezer probably lives amongst the Columbia River Basalts (CRB), a flood basalt province, or trap, that erupted at about the same time as the earliest Yellowstone eruption at McDermitt Caldera (~16 million years ago). CRB's are undoubtedly associated with the arrival of the Yellowstone plume head.
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CRB shown in green
source: http://geology.isu.edu/Digital_Geology_Idaho/Module10/mod10.htm
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Yes. In the North-East corner of the CRB. Here's a pic of some of the basalt and a view of the terrain from the top of Mount Geezer [;D] Pics were taken today. (Where's all the snow then?)
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Mt. Geisha?
House in photo certainly doesn't look Japanese. [::)]
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Tea ceremony conducted every day on big boulder at top of mountain. Mrs Geezer occupies white building. Mr Geezer home is translucent paper structure on left of picture. Very Japanese.
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With a massive caldera it holds the title for the ultimate volcano, it will happen, but when? that's the question