Yellowstone Supervolcano and Oxygen Isotopes
Tuesday, 6. November 2007, 19:43:33
My latest post was about hotspot volcanoes (Hawaii) and isotopes (helium), so let us move on from there. In 2005, erupted into public awareness in the made-for-TV movie Supervolcano, and suddenly the media were full of scaring stories about this hotspot supervolcano. Probably it will last another 1 million to 2 million years before a new supervolcano is born to the Northeast of the Yellowstone caldera. Nevertheless it presents a significant potential hazard to humankind. It is no surprise, then, that scientists are eager to uncover clues about Yellowstone’s past that could aid in predicting the volcano’s future behaviour. Last week Geotimes brought an article titled Yellowstone and Heise: Supervolcanoes That Lighten Up. If you have not heard of Heise, it is the supervolcano that erupted a few hundred thousand years before the event that produced the Yellowstone Caldera. It is located about 50 miles Southwest of Yellowstone.
Three massive explosive eruptions occurred at Yellowstone over the past 2.1 million years with a recurrence interval of about 600,000 to 800,000 years. Oxygen isotope signatures of individual crystals within volcanic rocks can help fingerprint the different magma sources. Oxygen atoms possess eight protons in their nucleus, but they may have eight, nine or 10 neutrons, yielding three possible oxygen isotopes: oxygen-16, oxygen-17 and oxygen-18. (See also my post on Climate Change and Scientific Language for more on oxygen isotopes) Magma formed from melting of the mantle or continental crust contains more oxygen-18 than shallow magma formed from melting of hydrothermally altered crust.
A few words on hydrothermal circulation (“hydro” meaning water and “thermal” meaning heat). Hydrothermal systems form when snow and rain water accumulate in pools and penetrate through fractures in the caldera, enabling the surface waters to circulate and become heated by hot, underlying magma. Snow and rain water contain “light” oxygen isotopes and when in contact with “normal,” accumulated volcanic rocks within the depressed caldera, oxygen from the water mixes with oxygen from the rocks. This results in oxygen-18-lowered rock and oxygen-18-enriched water. Hydrothermal waters can only travel up to a few kilometres below the surface, at which point any empty spaces in the rock are sealed off due to pressure. Thus, the light oxygen isotope fingerprint enables geologists to identify a near-surface environment as the source for these light magmas.
Being a hotspot volcano geologists originally thought that Yellowstone magmas were solely derived from continental crust and mantle material with heavier oxygen isotope signatures. Many volcanic fields of the Snake River Plain, including the Yellowstone Plateau, however contain magmas conspicuously low in the heavy oxygen-18 isotopes, giving the magmas so-called “light” signatures.
The authors suspect a cannibalisation process, where large swaths of hydrothermally altered volcanic material were remelted to produce “light” magmas. The sheer volume of the light magmas, some greater than 1,800 cubic kilometres, made them however ask themselves if it possible to generate such large volumes of oxygen-18-depleted magma by shallow remelting?
A positive note is that both Heise and Yellowstone produced three normal caldera-forming magmas and a series of light “cannibalised” post-caldera magmas. The final stage of volcanism in each volcanic field is marked by light magma eruptions.
Said with more scientific terms: “The occurrence of low ∂18O magmas at Heise and Yellowstone hallmarks a mature stage of individual volcanic cycles in each caldera complex. Sudden shifts in ∂18O of silicic magmas erupted from the same nested caldera complexes argue against any inheritance of the low ∂18O signature from mantle or crustal sources.”
If Heise is any indication, this could mean that the Yellowstone drama has entered its final act, but the volcano could exit with a climactic “big bang.” It is not known if the fourth caldera-forming eruption of Yellowstone will be analogous to the fourth and final caldera-forming light magma of Heise. Alternatively — and more likely — the Yellowstone supervolcano is geologically dead?
* http://www.geotimes.org/nov07/article.html?id=feature_yellowstone.html
* http://geology.geoscienceworld.org/cgi/content/abstract/35/11/1019
* http://gsa.confex.com/gsa/2007AM/finalprogram/abstract_132139.htm
* http://volcanoes.usgs.gov/yvo/
* http://volcanoes.usgs.gov/yvo/2006/uplift.html
* http://www.60secondscience.com/archive/earth-science/supervolcanic-time-bomb-aka-ye.php
See also my post on Yellowstone Super-volcano - http://my.opera.com/nielsol/blog/show.dml/164981
Three massive explosive eruptions occurred at Yellowstone over the past 2.1 million years with a recurrence interval of about 600,000 to 800,000 years. Oxygen isotope signatures of individual crystals within volcanic rocks can help fingerprint the different magma sources. Oxygen atoms possess eight protons in their nucleus, but they may have eight, nine or 10 neutrons, yielding three possible oxygen isotopes: oxygen-16, oxygen-17 and oxygen-18. (See also my post on Climate Change and Scientific Language for more on oxygen isotopes) Magma formed from melting of the mantle or continental crust contains more oxygen-18 than shallow magma formed from melting of hydrothermally altered crust.A few words on hydrothermal circulation (“hydro” meaning water and “thermal” meaning heat). Hydrothermal systems form when snow and rain water accumulate in pools and penetrate through fractures in the caldera, enabling the surface waters to circulate and become heated by hot, underlying magma. Snow and rain water contain “light” oxygen isotopes and when in contact with “normal,” accumulated volcanic rocks within the depressed caldera, oxygen from the water mixes with oxygen from the rocks. This results in oxygen-18-lowered rock and oxygen-18-enriched water. Hydrothermal waters can only travel up to a few kilometres below the surface, at which point any empty spaces in the rock are sealed off due to pressure. Thus, the light oxygen isotope fingerprint enables geologists to identify a near-surface environment as the source for these light magmas.
Being a hotspot volcano geologists originally thought that Yellowstone magmas were solely derived from continental crust and mantle material with heavier oxygen isotope signatures. Many volcanic fields of the Snake River Plain, including the Yellowstone Plateau, however contain magmas conspicuously low in the heavy oxygen-18 isotopes, giving the magmas so-called “light” signatures.
The authors suspect a cannibalisation process, where large swaths of hydrothermally altered volcanic material were remelted to produce “light” magmas. The sheer volume of the light magmas, some greater than 1,800 cubic kilometres, made them however ask themselves if it possible to generate such large volumes of oxygen-18-depleted magma by shallow remelting?
A positive note is that both Heise and Yellowstone produced three normal caldera-forming magmas and a series of light “cannibalised” post-caldera magmas. The final stage of volcanism in each volcanic field is marked by light magma eruptions.
Said with more scientific terms: “The occurrence of low ∂18O magmas at Heise and Yellowstone hallmarks a mature stage of individual volcanic cycles in each caldera complex. Sudden shifts in ∂18O of silicic magmas erupted from the same nested caldera complexes argue against any inheritance of the low ∂18O signature from mantle or crustal sources.”
If Heise is any indication, this could mean that the Yellowstone drama has entered its final act, but the volcano could exit with a climactic “big bang.” It is not known if the fourth caldera-forming eruption of Yellowstone will be analogous to the fourth and final caldera-forming light magma of Heise. Alternatively — and more likely — the Yellowstone supervolcano is geologically dead?
* http://www.geotimes.org/nov07/article.html?id=feature_yellowstone.html
* http://geology.geoscienceworld.org/cgi/content/abstract/35/11/1019
* http://gsa.confex.com/gsa/2007AM/finalprogram/abstract_132139.htm
* http://volcanoes.usgs.gov/yvo/
* http://volcanoes.usgs.gov/yvo/2006/uplift.html
* http://www.60secondscience.com/archive/earth-science/supervolcanic-time-bomb-aka-ye.php
See also my post on Yellowstone Super-volcano - http://my.opera.com/nielsol/blog/show.dml/164981
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