volcano

Photos: Volcanic eruption in Chile

The Puyehue volcano in the Andes Mountains in southern Chile is erupting. The Boston Globe has a set of 32 pictures showing the eruption and people dealing with the ash fall. The ash plume at the volcanic is six miles high and one mile wide.

See the photos here.

H/T to Syver More for bringing these to my attention.

Yellowstone Super Volcano Update

In a previous post I described the volcanic region of Yellowstone National Park and its history of volcanic eruptions. The Yellowstone super volcano is the youngest of a series of volcanoes that have erupted over the past 17 million years. During the last two million years, ash from each of three eruptions covered nearly half of the United States. Yellowstone is called a super volcano because its eruptions fall in the maximum range for explosiveness and volume of material ejected.

New research from the University of Utah shows that the volcanic plume of molten rock under Yellowstone, which would feed future eruptions, is bigger than previously thought.

A study in 2009, using seismic waves from earthquakes in the area estimated that the volcanic plume showed that “molten rock dips downward from Yellowstone at an angle of 60 degrees and extends 150 miles west-northwest to a point at least 410 miles under the Montana-Idaho border.”

The new study, using electrical conductivity measurements “shows the conductive part of the plume dipping more gently, at an angle of perhaps 40 degrees to the west, and extending perhaps 400 miles from east to west. The geoelectric image can ‘see’ only 200 miles deep.”

“The lesser tilt of the geoelectric plume image raises the possibility that the seismically imaged plume, shaped somewhat like a tilted tornado, may be enveloped by a broader, underground sheath of partly molten rock and liquids,” say the researchers. Although the research says nothing about when another eruption could occur, it implies that there is a potential for a very large, super eruption.

This research will be published in Geophysical Research Letters in a few weeks. Meanwhile, you can see more details and images in the press release here.

Humans and the Carbon Cycle

Some people must think that humans are not part of nature according to two comments to my post: Carbon Dioxide and the Greenhouse Effect . The comments alleged: “Human carbon emissions are not a part of the natural carbon cycle.” and “We are now releasing huge amounts of fossil carbon too rapidly for natural processes to adjust.” Both claim that human carbon dioxide emissions upset “the balance of nature.” This belief reflects a misunderstanding of what “balance” really is. Nature is never really “in balance” or static, it is always seeking equilibrium between forces that upset the status quo.

This misunderstanding is reflected in one of the comments: “The natural carbon cycle involves the production/consumption of carbon. Humans do exhale – but energy production involves humans using historic carbon from earlier carbon cycles that are not contemporary. It isn’t part of a ‘natural’ carbon cycle.”

Tell me, how can nature distinguish between a carbon dioxide molecule produced by someone burning wood in a fireplace versus carbon dioxide resulting from burning wood in a forest fire? How can nature distinguish between a molecule of carbon dioxide produced by burning coal to generate electricity versus coal burning in a seam due to natural spontaneous combustion? Yes, that does happen. So much for “historic carbon.”

There are actually two carbon cycles. The geologic carbon cycle stores carbon in limestone, dolomite, petroleum, and coal deposits. Carbon dioxide from the atmosphere is used up during the weathering of silicate rocks, a process that speeds up with increasing temperature or increasing carbon dioxide, thereby forming a negative feedback or thermostat. It takes millions of years, usually, for this carbon to cycle back into the biosphere. Volcanoes recycle carbonate rocks and emit 200 million metric tons of carbon dioxide per year according to the U.S. Geological Survey. There are also carbon dioxide gas seeps. Carbon dioxide is also produced from metamorphism of carbonate rocks.

The biologic carbon cycle is exchange of carbon dioxide between the atmosphere, biosphere, and ocean as shown in the graphic below. The biologic process involves photosynthesis, respiration, ocean absorption, and biological use of carbonates to form shells and other structures. Human emissions are part of these natural cycles.

 carbon-cycle-diagram

The relative amount of carbon in each “sink” is shown in the table below.

Carbon-sinks1

Notice that the amount of carbon stored as fossil fuel deposits is just one-tenth of that stored in the oceans, and the ocean store in continually in flux. The ocean is also the connection between the geologic carbon cycle and the biologic carbon cycle. As the amount of carbon dioxide in the atmosphere increases, ocean uptake also increases. The carbon dioxide is stored not only as dissolved gas, but also as carbonate ions which are sequestered by marine life and the production of limestone and dolomite deposits.

There is another complication. Some carbon is missing. When calculating the carbon flux, i.e., the emissions from known sources versus carbon sequestration by known sinks, there should be more carbon dioxide in the atmosphere than there is. So, either there is an unknown process taking up carbon dioxide or a known process is working faster than we thought (seeking equilibrium).

There is some observational evidence for that last process. We see that terrestrial plant life has increased its net primary productivity by growing more robustly and by making better use of nitrogen in the soil. (See here ) There are also new studies showing that small marine creatures, such as Thaliacea, are depositing more carbon into the geologic sink than previously realized.

Perhaps we still don’t know as much about the carbon cycle as we thought.

To put things in perspective, according to data from the Energy Information Administration, based on data derived from the IPCC, human carbon dioxide emissions represent about 3% of the total carbon dioxide flux, and 98.5% of that is reabsorbed in the biologic carbon cycle. (Source )

Slightly off subject but important: A new paper in Geophysical Research Abstracts (Vol. 13, EGU2011-4505-1, 2011) based on detailed spectrographic analysis of the atmosphere found that because the absorbance of water vapor overlaps the frequencies of long wave radiation that are absorbed by carbon dioxide and methane, the effective sensitivity of carbon dioxide and methane as greenhouse gases is only one-seven that claimed by the IPCC and used in climate models.

That makes our emissions from burning fossil fuels of even less concern.

The Yellowstone Super Volcano

Yellowstone National Park in northwest Wyoming is a picturesque land of geysers, hot springs, waterfalls, mountains, and lakes. But just in case you don’t have enough to worry about, it is also the largest supervolcano in North America and among the top three largest in the world. The term “supervolcano” refers to a measure of volume of material erupted and explosiveness. See comparison charts for volume here and the volcanic explosivity index here. You will see that the Yellowstone supervolcano is at the maximum end of both scales.

The U.S. Geological Survey (USGS) map below shows the general setting of the Yellowstone volcano and caldera. Calderas are created following an eruption when the volcano collapses in on itself.

Yellowstone-caldera-overview

According to the Yellowstone Volcano Observatory, run by the USGS and the University of Utah, during the past 2 million years the Yellowstone super volcano has had three of the world’s largest volcanic eruptions:

Eruption of the >2450 cu km Huckleberry Ridge Tuff about 2.1 million years ago created the more than 75-km-long Island Park caldera.

The second cycle concluded with the eruption of the Mesa Falls Tuff around 1.3 million years ago, forming the 16-km-wide Henrys Fork caldera at the western end of the first caldera.

Activity subsequently shifted to the present Yellowstone Plateau and culminated 640,000 years ago with the eruption of the >1000 cu km Lava Creek Tuff and the formation of the present 45 x 85 km caldera. Resurgent doming subsequently occurred at both the NE and SW sides of the caldera and voluminous (1000 cu km) intracaldera rhyolitic lava flows were erupted between 150,000 and 70,000 years ago.

Yellowstone is presently the site of one of the world’s largest hydrothermal systems including Earth’s largest concentration of geysers. As such, it could be one of the largest sources of geothermal-produced electricity, but that’s not likely to happen.

The USGS map below shows the coverage of ash deposits from the three major eruptions, compared to the 1980 eruption of Mount St. Helens. The map also shows the extent of the Bishop Tuff which erupted from the Long Valley volcano in California 760,000 years ago.

Yellowstone map 2

The Yellowstone super volcano is the youngest of a series of such volcanoes that have erupted over the past 17 million years. The older volcanoes trace a line running up the Snake River Plain. The graphic below shows the location and age of these volcanoes. Notice also the parabolic shape of earthquake epicenters (red dots).

Yellowstone map 3

The theory of this volcanic region is that there is a stationary “hot spot” in the mantle that periodically breaks the surface with an eruption. Eruptions occur in a linear pattern showing that the continental crust is moving over the hot spot at about 2.8 cm/yr at an azimuth of about 247 degrees according to Smith et al. “The Yellowstone hotspot has been the source of voluminous rhyolite tuffs and lavas with eruptions often having volumes of hundreds to thousands of cubic kilometers and representing some of the largest Quaternary eruptions on Earth.”

A similar hot spot occurs under Hawaii. In Hawaii, the magma is basaltic which is very fluid so eruptions are relatively tame: volcanic explosivity index (VEI) 0 to 1. In Yellowstone, however, the magma is rhyolitic, very thick and viscous. That makes for violent explosions (VEI 8, the maximum) which produces ash rather than lava flows.

Geophysical investigations show that the Yellowstone magma chamber is 6- to 16 km deep beneath the caldera. Under that, the feeder zone to the magma chamber extends 660 km into the mantle transition zone.

What is happening now?

The National Park Service assures us, “There is no evidence that a catastrophic eruption at Yellowstone National Park (YNP) is imminent. Current geologic activity at Yellowstone has remained relatively constant since earth scientists first started monitoring some 30 years ago. Though another caldera-forming eruption is theoretically possible, it is very unlikely to occur in the next thousand or even 10,000 years. Scientists have also found no indication of an imminent smaller eruption of lava.”

On the other hand, National Geographic news of January 19, 2011 reports:

Yellowstone National Park’s supervolcano just took a deep “breath,” causing miles of ground to rise dramatically, scientists report.

But beginning in 2004, scientists saw the ground above the caldera rise upward at rates as high as 2.8 inches (7 centimeters) a year.

The rate slowed between 2007 and 2010 to a centimeter a year or less. Still, since the start of the swelling, ground levels over the volcano have been raised by as much as 10 inches (25 centimeters) in places.

“It’s an extraordinary uplift, because it covers such a large area and the rates are so high,” said the University of Utah’s Bob Smith, a longtime expert in Yellowstone’s volcanism.

Scientists think a swelling magma reservoir four to six miles (seven to ten kilometers) below the surface is driving the uplift. Fortunately, the surge doesn’t seem to herald an imminent catastrophe, Smith said.

(Related story with 3D model of magma chamber: “Under Yellowstone, Magma Pocket 20 Percent Larger Than Thought.”)

“At the beginning we were concerned it could be leading up to an eruption,” said Smith, who co-authored a paper on the surge published in the December 3, 2010, edition of Geophysical Research Letters.

“But once we saw [the magma] was at a depth of ten kilometers, we weren’t so concerned. If it had been at depths of two or three kilometers [one or two miles], we’d have been a lot more concerned.”

Here is a graphic from Smith, showing topographic swelling caused by magma pressure at Yellowstone; rather impressive:

Yellowstone map 4

Apparently, all is (relatively) quiet on the western front, but who knows when the pimple will pop.

Reference:

Smith, R.B., et al., 2009, Geodynamics of the Yellowstone hotspot and mantle plume: Seismic and GPS imaging, kinematics, and mantle flow, Journal of Volcanology and Geothermal Research 188 (2009) 26–56. http://www.uusatrg.utah.edu/PAPERS/smith_jvgr2009complete.pdf

See update:

https://wryheat.wordpress.com/2011/04/13/yellowstone-super-volcano-update/ 

Geologic Setting of Icelandic Volcanoes

The ash spewing from the Eyjafjallajokull volcano in Iceland is disrupting air traffic throughout Europe. Volcanic ash is essentially sharp-edged glass with particles ranging from sand-sized to microscopic. These particles can wreak havoc with jet engines and your lungs. The last time this volcano erupted, the eruption lasted more than a year, from December 1821 until January 1823.

Iceland sits astride the Mid-Atlantic Ridge, a boundary between two tectonic plates, where new crust is being formed by volcanic eruptions as the plates diverge, i.e., they are moving away from each other. Movement on this structure over the last 180 million years or so has separated Europe from North America, and Africa from South America. The island of Iceland is engaged in a geologic race between the spreading motion which is ripping the island apart, and the volcanoes which are building the island up.

Other islands of the Atlantic Ocean created by the volcanism of the Mid-Atlantic Ridge are The Azores, Bermuda, Madeira, The Canary Islands, Ascension, St. Helena, and Tristan da Cunha. But, you probably haven’t heard about any volcanoes erupting in Bermuda because that island group lacks one other geologic phenomenon: the “hot spot.” Iceland also sits above a mantle plume or “hot spot” where magma from deep in the mantle forces its way to the surface. The Hawaiian Islands were formed, and are being formed, by such a hot spot. In Hawaii, the westward movement of the Pacific plate passes over this hot spot and eruptions produce new islands. Iceland, however, is not moving in such a manner.

map_plate_tectonics_world

The general geology of Iceland is shown on the map below from the Nordic Volcanology Institute.

Iceland-geo_map

The pink area on the map represents the rifts along the Mid-Atlantic Ridge where the crust is separating and the volcanoes are most active. Of Iceland’s 100 most active volcanoes, 25 have erupted in recent history, and 35 volcanoes have erupted in the last 10,000 years. Eleven volcanoes have erupted between 1900 and 1998. Most of the eruptions were from fissures or shield volcanoes and involve the effusion of basaltic lava.

The 1783 to 1784 eruption at Laki fissure and the adjoining Grímsvötn volcano was the largest single historic eruption of basaltic lava (12 cubic km). Benjamin Franklin, who at the time was serving as ambassador to France remarked on this eruption. The ash cloud caused the “year without summer.” That eruption of basalt lava and clouds of poisonous hydrofluoric acid/sulfur-dioxide compounds killed over 50% of Iceland’s livestock population, leading to famine which killed approximately 25% of the population. It remains to be seen if the current eruption will be as long lasting. So far, the ash cloud from the current eruption has risen to 30,000 feet which affects airline travel, but it has stayed below the stratosphere, so the climate effects are not likely to be as drastic as those in 1783.

The Boston Globe has a series of photographs of the volcano and flooding it caused. Boston Globe photos: http://tinyurl.com/y6vslk4

Tucson Mountains Chaos

“Tucson Mountain Chaos is a formal geologic name, describing one of the more confusing, complex, and controversial areas in southern Arizona.” So says the newsletter of the Arizona Geological Society.

If you drive over Gates Pass and look closely at the road cuts, you will see a jumble of various-colored rocks. Within the beds of volcanic ash are big chunks of other volcanics, limestones, granites, and schists. The mountain range appears to be composed of a mega-breccia.

The origin of the Tucson Mountains is still subject to geologic debate. The following is what I think is the most probable chain of events. Like many stories in the very complex structural geology of the Western U.S., even the probable may seem fantastic.

[NOTE:  New evidence obtained since this article was written shows that the caldera did not form over the Catalina Mountains as postulated below. See:

https://wryheat.wordpress.com/2016/08/30/tucson-mountains-geology-an-update/

for updated information.]

 

Our story begins during the Laramide Orogeny, when the Rocky Mountains were being built about 70 million years ago. The North American continent was speeding westward at 2 inches a year and it was crashing into oceanic crust under the Pacific Ocean. The heavier oceanic crustal rocks dove under (were subducted beneath) the lighter continental crust. This caused compression, mountain building, and volcanism.

As subduction of the ocean crust continued, it reached a depth that was hot enough to melt it. Great blobs of magma rose like balloons through the continental crust. Some of these blobs became the copper deposits we have in Arizona, others reached the surface and became volcanoes.

One such volcano was formed where the Catalina Mountains are now, east of Tucson. It was a large volcano that erupted in violent explosions which eventually caused collapse of the volcanic edifice to form a caldera about 10 miles across.

Portions of the wall rocks fell into the caldera. This probably accounts for the chaotic mixture of rocks in the Tucson Mountains. But that’s just half of the story.

If the volcano was east of where Tucson is now, how did the rocks wind up to the west of the city?

The North American continent was still moving westward. Sometime between 40- and 20 million years ago it overrode a spreading center called the East Pacific Rise. This area was similar to the spreading center of the Mid-Atlantic ridge that gradually separated Africa from South American, and Europe from North America. Today, this western spreading center runs up the Gulf of California and separates Baja from mainland Mexico. It is also the driver of the San Andreas fault in California.

The compression that built the Rocky Mountains was turned into extension. The western part of the American continent began to be torn apart.

By about 30 million years ago, crustal stretching and heating from below, arched-up the area beneath the “Tucson Mountains” volcano. It may have looked something like Figure A.

tm-01

About 25 million years ago, stretching caused low-angle faulting to detach much of the volcanic edifice from underlying rocks. The volcano and its caldera began to slide to the west. (Figure B).

tm-021-300x110

By the way, detachment faults crop out along the western base of the Catalina Mountains, amid all that nice expensive foothills property.  Sometime between 12- and 6 million years ago, the on-going crustal stretching reached a limit and things started to break. High-angle faults formed. This produced the Basin and Range topography we have now. (Figure C.)

tm-03

As the valleys dropped, erosion filled them with debris from the mountains. The glacial epochs added water. (Figure D)

tm-04

 

The Tucson Mountains represent just one example of the consequences of crustal stretching. Picacho Peak has a similar history. Near Green Valley, the old Twin Buttes mine, the Mission mine, and the Eisenhower pit are a few pieces of what once was one deposit that got sliced up and fanned out like a deck of cards.

Many geologists disagree that the Tucson Mountain volcano formed over the Catalina Mountains, rather, they think the volcano is where the rocks now sit. The main evidence they cite is that the chemistry of the volcanics in the Tucson Mountains is incompatible with the proposed generating pluton in the Catalina Mountains. They also cite structural inconsistencies. Notice in the last cross-section the Tucson Mountain volcanics dip to the east (left) as would be consistent with the story above. However, other rocks in the Tucson Mountains dip to the west and the volcanics of Tumamoc Hill are horizontal. That may negate the detachment theory. If this latter hypothesis is correct, then the volcanics of the Tucson Mountains represent the west half of a caldera. The rest of it is buried in the Tucson Valley to the east.

In either case, it remains the Tucson Mountain Chaos.

References:

Lipman, Peter, 1993, Geologic map of the Tucson Mountains Caldera, southern Arizona, U.S.G.S. IMAP 2205.

Scarborough, Robert, The Geologic Origin of the Sonoran Desert, Arizona-Sonora Desert Museum, http://www.desertmuseum.org/books/nhsd_geologic_origin.php

The graphics used in this article came from this paper.