Featured Research

from universities, journals, and other organizations

Technique Measures Heat Transport In The Earth's Crust

Date:
April 7, 2009
Source:
Washington University in St. Louis
Summary:
Putting a new spin on an old technique, a research professor of earth and planetary sciences has revolutionized scientists' understanding of heat transport in the Earth's crust, the outermost solid shell of our planet.

Anne Hofmeister, WUSTL research professor of earth and planetary sciences in Arts & Sciences, places a rock sample for laser-flash analysis. A technique she has refined provides much more accurate data on heat transport through rocks than conventional methods. Her advance brings scientists closer to a better understanding of the Earth's interior.
Credit: David Kilper/WUSTL Photo Services

Putting a new spin on an old technique, Anne M. Hofmeister, Ph.D., research professor of earth and planetary sciences in Arts & Sciences at Washington University in St. Louis, has revolutionized scientists' understanding of heat transport in the Earth's crust, the outermost solid shell of our planet.

Temperature is an important driver of many geological processes, including the generation of magmas (molten rocks) in the deepest parts of the Earth's crust, about 30 to 40 kilometers below the surface. Yet, until recently, temperatures deep inside the Earth's crust were uncertain, mainly because of difficulties associated with measuring thermal conductivity, or how much heat is flowing through the rocks that compose the crust.

In conventional methods of measuring thermal conductivity, measurement errors arise as the temperature of a rock nears its melting point. At such high temperatures, heat is not just transported from atom to atom by vibrations, but also by radiation (light). Since conventional methods cannot separate heat flow carried by vibrations from that associated with radiation, most measurements of how efficiently rocks transport heat at high temperatures have been overestimated. Because of this experimental uncertainty, scientists have assumed rock conductivity to be constant throughout the crust in order to make advances in models describing Earth's geological behavior.

Laser-flash analysis

Using an industrial laser that is typically used for steel welding, Hofmeister was able to circumvent the problems that plagued the older methods. Her facility at WUSTL is the first in the world to employ such a laser for geoscience research.

Her technique, laser-flash analysis, provides much more accurate data on heat transport through rocks than conventional methods. In laser-flash analysis, a rock sample is held at a given temperature and then subjected to a laser pulse of heat, allowing Hofmeister to measure the time it takes for the heat to go from one end of the sample to the other. This measurement of thermal diffusivity, or how fast heat flows through matter, is another way to describe the thermal conductivity of a rock.

Since measuring heat transport in the crust itself is impossible, Hofmeister used the laser to measure heat transport in individual rock samples at various temperatures and then averaged across samples to represent the dynamics of the crust. In collaboration with researchers from the University of Missouri - Columbia, Peter I. Nabelek, Ph.D., professor of geological sciences, and Alan G. Whittington, Ph.D., assistant professor of geological sciences, Hofmeister applied her findings to explain geological phenomena observed in the environment.

The results, published in Nature on March 19, 2009, suggest that rock conductivity is not constant as was previously assumed, but instead varies strongly with temperature. Hofmeister explains, "Our analysis shows that rocks are more efficient at conducting heat at low temperatures than was previously thought and less efficient at high temperatures. The process of moving heat around really depends on the temperature of the rocks."

Hofmeister and her collaborators found that the conductivity of rocks in the lower crust, where the external temperature is very high, is much lower — by as much as 50 percent — than was predicted by conventional methods. These results also suggest that the lower crust may be much hotter than scientists previously recognized. Since rocks become better insulators and poorer conductors at high temperatures, the lower crust acts like a blanket over the heat-generating mantle, the layer underlying the crust.

Magma machine

The observation that the lower crust is a good thermal insulator has broad implications for scientists' understanding of fundamental geological processes such as magma production.

Hofmeister explains, "The new methods change our understanding of how heat is transported in geological environments. This pertains to where you find magmas, where you cook metamorphic rock, and where lavas form on ocean ridges."

She and her colleagues used the new temperature-dependent data to inform computer models that predict the consequences of burying and heating up rocks during mountain belt formation, as occurs in the present-day Himalayas. While prior models relied upon extraordinary processes such as high levels of radioactivity to explain melting of the crust in the Himalayas, Hofmeister and her collaborators' work suggests that the thermal properties of the rocks themselves might be sufficient to generate magmas.

In particular, they find that the strain heating, or friction, caused by mountain belt formation can trigger crustal melting. Because the lower crust is such a good thermal insulator, strain heating is much faster, more efficient, and more self-perpetuating than previously recognized.

"The melt is more insulating than the rock," explains Hofmeister, "Once you get rocks melting, the thermal diffusivity goes down, which makes it harder to cool the rocks. They stay hot longer and there's the potential for more melting."

According to Hofmeister, the Himalaya situation described in the study is probably not unique. Because heat transport is such an important driver, many models of Earth's geological behavior will need to be revisited in light of Hofmeister and her collaborators' findings.

These advances bring Hofmeister much closer to accomplishing what she describes as her life-long career objective. "The goal for most of my career has been to determine the temperature inside the earth. It's the time dependence, how long it takes heat to flow through rocks, that is going to tell us how hot the interior is," she says.

According to Hofmeister, understanding the temperature of the Earth's interior is the first step towards understanding the thermal evolution of the earth.


Story Source:

The above story is based on materials provided by Washington University in St. Louis. Note: Materials may be edited for content and length.


Cite This Page:

Washington University in St. Louis. "Technique Measures Heat Transport In The Earth's Crust." ScienceDaily. ScienceDaily, 7 April 2009. <www.sciencedaily.com/releases/2009/03/090330165810.htm>.
Washington University in St. Louis. (2009, April 7). Technique Measures Heat Transport In The Earth's Crust. ScienceDaily. Retrieved September 18, 2014 from www.sciencedaily.com/releases/2009/03/090330165810.htm
Washington University in St. Louis. "Technique Measures Heat Transport In The Earth's Crust." ScienceDaily. www.sciencedaily.com/releases/2009/03/090330165810.htm (accessed September 18, 2014).

Share This



More Earth & Climate News

Thursday, September 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Scientists Examine Colossal Squid

Raw: Scientists Examine Colossal Squid

AP (Sep. 16, 2014) — Squid experts in New Zealand thawed and examined an unusual catch on Tuesday: a colossal squid. It was captured in Antarctica's remote Ross Sea in December last year and has been frozen for eight months. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Man Floats for 31 Hours in Gulf Waters

Man Floats for 31 Hours in Gulf Waters

AP (Sep. 16, 2014) — A Texas man is lucky to be alive after he and three others floated for more than a day in the Gulf of Mexico when their boat sank during a fishing trip. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Researchers Explore Shipwrecks Off Calif. Coast

Researchers Explore Shipwrecks Off Calif. Coast

AP (Sep. 16, 2014) — Federal researchers are exploring more than a dozen underwater sites where they believe ships sank in the treacherous waters west of San Francisco in the decades following the Gold Rush. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Isolated N. Korea Asks For International Help With Volcano

Isolated N. Korea Asks For International Help With Volcano

Newsy (Sep. 16, 2014) — Mount Paektu volcano in North Korea is showing signs of life and there's not much known about it. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins