Redoubt from Ninilchik, AK. Image courtesy of Calvin Hall.
It has been a few days since we've talked about Redoubt. Well, it might be because the volcano has settled down for the past week, to the point that AVO put the volcano back to Orange/Watch status last week and hasn't had to go back to Red/Warning since. This is not to say the Redoubt is quiet, on the contrary, there is still elevated seismicity, an almost-constant steam/ash plume up to 15,000 feet / 5,000 meters and most importantly, the new dome (below) is still growing near the summit. The system has been actively degassing carbon dioxide and sulfur dioxide at much as 10,000 tons/day and the USGS is quoted as saying that
"...these volcanic gas emission rates are among the largest ever measured in Alaska, though such high values are consistent with an openly degassing volcanic system that is actively extruding lava."
The area of active dome growth on Mt. Redoubt. Image courtesy of AVO/USGS by Heather Bleick. Taken on April 5th, 2009.
Right now, the big concern with residents around the volcano will be how Redoubt might impact the upcoming tourist season in the Cook Inlet area. New explosions and eruptions might disrupt air travel to the area enough to affect the salmon fishing season in Alaska negatively. And, of course, we have the ongoing saga of the Drift River Oil Terminal. The shutdown of the terminal has derailed oil production in the Inlet and there is even talk of a permanent shutdown of the terminal. These two major economic resources for Alaska - tourism and oil - will be the stories to follow as Redoubt continues to rumble.
10,000 tons/day EACH of carbon dioxide and sulfur dioxide? Or combined? It's my understanding that the typical proportion of CO2 to SO2 is like 3 to 1. Have I got that wrong, or is there just a wide range of variation among volcanoes, or even at a single volcano over time?
I am no expert on volcanic gas emissions (however, I'm sure some of my readers are), but the exact wording in the USGS release about the activity was "Emissions of both CO2 and sulfur dioxide (SO2) have been very elevated, sometimes reaching levels in excess of 10,000 tonnes/d.", so it seems that it is tonnes of each. Volcanic gases emissions can be quite variable between volcanoes and between eruptions - it really will depend on the compositional nature of the magma and how/when the volatiles get released by the system.
Where does the CO2 in volcanoes come from? Itâs not SUVâs. Itâs not people exhaling. Itâs not from soda. The SO2 could be a byproduct of sulfur in the magma. Where does the oxygen for both CO2 & SO2 come from? What compares with 10,000 tons of CO2 per day? X number of cars? Thank you in advance.
The most common volatile in magma is water, so there is a lot of oxygen there, but even beyond that, most minerals (and liquid magma for that matter) have quite a bit of oxygen in their structures in the crystal or in the network of silica polymers that make up the magma itself. So, plenty of oxygen to go around. As for the carbon, there are plenty of sources of carbon within the crust that magma pass through, or even in primordial carbon from the mantle (along with fluids released from the subducting slab in arc settings), so it isn't really much of a surprise to find so much CO2 (and SO2 for that matter) in magmas.
As for the output, the U.S. releases 8,000,000 tonnes of CO2 per day from the burning of gasoline alone, so 10,000 tonnes from a single volcano (0.1%) isn't really that big compared to the human output. It just seems like a lot because a volcano is a point source.
The volcanic CO2 comes from the breakdown of carbonates that have been carried deep into the earth. The equilibrium of the Urey reactions favors silicates at high temperatures, and carbonates at low temperatures. The CO2 in the carbonates is essentially atmospheric CO2 which was sequestered by the weathering of silicate rocks on the earths surface. This has been to slow process which has kept the earths temperature with reasonable limits for billions of years. Weathering, which dramatically increases in efficiency draws down atmospheric CO2 until the temperature lowers enough to slow down the weathering. After millions of years the resulting carbonates are subducted into the mantle and heated, releasing the CO2. Silicate rich magmas then provide new rock for the process to repeat.
Thanks for that explanation, Big Tom!
Thank you both for the education.
They have installed a new camera at Redoubt that zooms in on the dome. Easily the best view of the dome so far, it is worth a look.