Research opens fresh view on volcanic plumbing systems

July 10, 2017, University of Oregon
The iconic El Capitan at Yosemite National Park in California contains a long-running record of magma injections that never breached the surface, instead freezing into the Earth's crust. Credit: Greg M. Stock, National Park Service

Volcanic eruptions such as Mount St. Helens' in 1980 show the explosiveness of magma moving through the Earth's crust. Now geologists are excited about what uplifted granite bodies such as Yosemite's El Capitan say about magma that freezes before it can erupt on the surface.

These granite structures, called magmatic intrusions, form incrementally over time by small pulses of magma that cool and crystalize 5 to 20 kilometers—3 to 12 miles—underground. Many are uplifted and exposed by erosion. They also contain the history of magma injections that occurred tens to hundreds of millions of years ago, says Leif Karlstrom of the University of Oregon.

In a paper placed online July 10 by the journal Nature Geoscience, a three-member research team led by Karlstrom unveiled a new framework for understanding what the pattern of volcanoes seen at the surface implies about the structure of subsurface magma plumbing systems. Some 50 to 90 percent of magma, Karlstrom said, doesn't get through the crust.

"Granitic landscapes in the Yosemite Valley in California and in the North Cascades are iconic, huge cliffs with exposed rock," he said. "If you look closer, the structure of that landscape shows all kinds of intrusive bodies that record different pulses of magma coming into the crust. Our findings hopefully allow you to stare up at El Capitan and make sense of it in some new way."

In the National Science Foundation-funded research, Karlstrom, Scott R. Paterson of the University of Southern California and A. Mark Jellinek of the University of British Columbia examined more than a decade of measurements of size distributions of igneous rock intrusions in the North American Cordillera.

Magma rising in active volcanic regions in places such as the Cascades, Hawaii and Iceland, Karlstrom said, often occurs as narrow, sheet-like intrusions commonly called dikes and sills. This occurs as a cracking process in brittle crustal rocks. Over long timescales, however, the process changes.

These changes are part of a transition into a "reverse energy cascade," in which rising magma injections become trapped and lose energy, the researchers say.

Magma mixes and merges with surrounding rocks as it cools and crystalizes. Heat lost from repeated injections of magma continues to heat crustal rocks, building and the expanding granitic intrusive complexes formed by frozen magma in a viscous, rather than brittle, manner. The resulting structures are seen today where the formations are exposed.

"That act of dumping heat into the crust over time changes the nature of the mechanical response to injections of magma," Karlstrom said. "The earth's crust is a filter for rising melts. You have magma that is generated deep in the earth, and somehow it gets to the surface carrying heat and volatiles, such as carbon dioxide. How that happens is through the crustal magma transport system."

Studying the processes behind injections over long timescales, he said, helps build better understanding of volcanoes, their impacts on global climate and where large volcanoes are likely to occur.

"This paper hits on one of the primary current research problems in volcanology," Karlstrom said. "We are able to make a strong statement about the connection of deep intrusive magmatism to the surface expression of volcanism. We think that what we found provides a framework for understanding other kinds of problems related to magmatism on Earth and other planets."

Explore further: Magma reservoirs key to volcanic eruptions

More information: Leif Karlstrom et al, A reverse energy cascade for crustal magma transport, Nature Geoscience (2017). DOI: 10.1038/ngeo2982

Related Stories

Volcanic crystals give a new view of magma

June 15, 2017

Volcanologists are gaining a new understanding of what's going on inside the magma reservoir that lies below an active volcano and they're finding a colder, more solid place than previously thought, according to new research ...

Popcorn-rocks solve the mystery of the magma chambers

November 2, 2016

Since the 18th century, geologists have struggled to explain how big magma chambers form in the Earth's crust. In particular, it has been difficult to explain where the surrounding rock goes when the magma intrudes. Now a ...

Modeling magma to find copper

January 12, 2017

Copper is an essential element of our society with main uses in the field of electricity and electronics. About 70% of the copper comes from deposits formed several million years ago during events of magma degassing within ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

EPA adviser is promoting harmful ideas, scientists say

March 22, 2019

The Trump administration's reliance on industry-funded environmental specialists is again coming under fire, this time by researchers who say that Louis Anthony "Tony" Cox Jr., who leads a key Environmental Protection Agency ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Caliban
3 / 5 (2) Jul 10, 2017
Interesting --at least to me-- that these researchers(in terms of this article) completely ignore the role of active plate tectonics and the resulting faulting, folding, and deformation of the crust as having any effect upon upon the timing, location, or scale of magmatic intrusion.
Nik_2213
not rated yet Jul 10, 2017
I suppose the question is why such magma pulses halted where they did, rather than intrude as dykes & sills, or break surface. Yes, there's much intricate geochemistry at play within and between existing rock masses and incoming, but what makes a particular pulse 'stick or twist' ??

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.