"Long before it's in the papers"
January 27, 2015


Study suggests method to predict eruptions

Feb. 16, 2014
Courtesy of University of California - Davis
and World Science staff

There may be a way to pre­dict vol­can­ic erup­tions with some re­li­a­bil­ity af­ter all: de­tect­ing wheth­er the mol­ten rock un­der a vol­ca­no is in a liq­uid enough state to erupt, sci­en­tists say.

That could nar­row down by at least 90 per­cent the time win­dows dur­ing which eruption is known to be pos­si­ble, they ex­plain. Seis­mic im­ag­ing or oth­er re­mote im­ag­ing meth­ods could be used to check the mol­ten rock’s state, said Kari Coop­er, a ge­ol­o­gist at the Uni­vers­ity of Cal­i­for­nia, Da­vis, who co-authored the stu­dy, pub­lished on­line Feb. 16 in the jour­nal Na­ture.

Rocks ejected from Mt. Hood show that the mag­ma un­der the vol­ca­no has been liq­uid enough to erupt for less than 10 per­cent of the last 20,000 years, sci­en­tists say. If gen­er­al­ly true, this could have im­pli­ca­tions for un­derstanding when a vol­ca­no is most ready to erupt. (Cred­it: Er­ic Kle­met­ti, Den­i­son U.)

For eruption to oc­cur, the mag­ma, or mol­ten rock un­der the vol­ca­no must be “mo­bile” enough to erupt. “The ques­tion is, what per­centage of time is the mag­ma in an eruptible state?” said Coop­er. “Peo­ple think about there be­ing this big res­er­voir of liq­uid mag­ma un­der a vol­ca­no, but we don’t think it’s in that state all the time.”

The mo­bil­ity of the mag­ma de­pends on the amount of crys­tall­iz­a­tion: when it is more than about 50 per­cent crys­talline, it be­comes immo­bile, she said. Crys­tall­iz­a­tion, in turn, de­pends on the tem­per­a­ture of the rock.

Un­til now, vol­ca­nol­o­g­ists haven’t known how com­mon it is for mag­ma to be crys­talline vs. eruptible, Coop­er said. The new work shows that at least for Mount Hood, Ore., the mag­ma is mo­bile less than 10 per­cent, and per­haps as lit­tle as one per­cent of the time.

Coop­er and Or­e­gon State Uni­vers­ity ge­ol­o­gist Ad­am Kent stud­ied rocks ejected from pre­vi­ous erup­tions at Mount Hood. By an­a­lyz­ing both ra­di­o­ac­t­ive iso­topes, or var­i­ant forms of el­e­ments, and the dis­tri­bu­tion of trace el­e­ments, they re­con­struct­ed the his­to­ry of the rocks and the con­di­tions they were un­der be­fore blast­ing out.

A pre­lim­i­nar­y sur­vey of da­ta from si­m­i­lar vol­ca­noes around the world sug­gests they fol­low a si­m­i­lar pat­tern—erupt­ible mag­ma is only there a small frac­tion of the time, said the re­search­ers, who plan fur­ther stud­ies.

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There may be a way to predict volcanic eruptions with some reliability after all: detecting whether the molten rock under a volcano is in a liquid enough state to erupt, scientists say. That could narrow down by at least 90 percent the time windows during which eruption is known to be possible, they explain. Seismic imaging or other remote imaging methods could be used to check the molten rock’s state, said Kari Cooper, a geologist at the University of California, Davis, who co-authored the study, published online Feb. 16 in the journal Nature. For eruption to occur, the magma, or molten rock under the volcano must be “mobile” enough to erupt. “The question is, what percentage of time is the magma in an eruptible state?” said Cooper. “People think about there being this big reservoir of liquid magma under a volcano, but we don’t think it’s in that state all the time.” The mobility of the magma depends on the amount of crystallization: when it is more than about 50 percent crystalline, it becomes immobile, she said. Crystallization, in turn, depends on the temperature of the rock. Until now, volcanologists haven’t known how common it is for magma to be crystalline vs. eruptible, Cooper said. The new work shows that at least for Mount Hood, Ore., the magma is mobile less than 10 percent, and perhaps as little as one percent of the time. Cooper and Oregon State University geologist Adam Kent studied rocks ejected from previous eruptions at Mount Hood. By analyzing both radioactive isotopes, or variant forms of elements, and the distribution of trace elements, they reconstructed the history of the rocks and the conditions they were under before blasting out. A preliminary survey of data from similar volcanoes around the world shows that they likely follow a similar pattern to Mount Hood, with eruptible magma only there a small fraction of the time, said the researchers, who plan further studies.