20 Scientific American, October 2020ALAMYADVANCES
G E O L O G YMagma
Far Afield
One third of volcanoes may have
molten reservoirs kilometers awayMagma—the molten rock that nourishes
volcanoes—can lurk in underground pock-
ets surprisingly far from where it emerges,
new research shows. This means the
instruments placed on a volcano’s flanks
might fail to pick up signs of moving mag-
ma that can signal an impending eruption.
University of Oregon volcanologist Allan
Lerner and his colleagues focused on 56
volcanoes in subduction zones (geologically
active areas where one tectonic plate is div-
ing under another) on five continents for a
new paper, published in July in Geophysical
Research Letters. Compiling volcano data
from other studies, the team estimated the
center of each volcano’s magma reservoir
and compared it with the estimated center
of the volcano’s aboveground portion. The
reservoirs had been found through process-
es such as measuring the earth’s surface
moving up or down and tracing how the
planet’s crust conducts electricity.
The researchers calculated that rough-
ly one third of volcanoes were more than
four kilometers away from their magma
reservoirs. Five volcanoes, including
two in Japan, two in Indonesia and one
in Mexico, had offsets of more than
10 kilometers. “It was a surprise,” Lerner
says, because a long-standing tenet of
volcan ology is that magma reservoirs arelocated directly underneath volcanoes.
Offset magma reservoirs have been
reported before, but the researchers say
their investigation is the first to focus on
an ensemble of volcanoes. Thanks to their
large sample size, Lerner and his collabo-
rators were also able to demonstrate cor-
relations. They showed that smaller volca-
noes tended to be farther from their mag-
ma reservoirs than larger volcanoes. This
makes sense, the team suggests, because
geologic structures such as fault lines
essentially create an underground obstacle
course for magma. The large quantities
of magma that feed big volcanoes carry
enough heat to blow straight through such
natural boundaries, but the smaller reser-
voirs associated with smaller volcanoes
must forge convoluted paths to the sur-
face. “In small volcanoes, the magma that
ascends is kind of at the mercy of preexist-
ing crustal structures,” Lerner says.
These results have implications for how
volcanoes are monitored. Researchers
usually aim to place ground-based instru-
ments on or near a volcano, says Diana
Roman, a volcanologist at the Carnegie
Institution for Science, who was not
involved in the research. But this new study
indicates that such a strategy might not be
best. “This tells us we should be looking
farther afield, especially for volcanoes with
relatively small edifices,” Roman says.
Studying more volcanoes, including
those not in subduction zones, would be
valuable to see if these same trends persist,
Lerner says: “A very clear next direction
would be to expand this study to look at
volcanoes in other tectonic settings.”
— Katherine KorneiSouth Sister volcano in Oregon
has an offset magma reservoir.20 Scientific American, October 2020ALAMYADVANCES
G E O L O G YMagma
Far Afield
One third of volcanoes may have
molten reservoirs kilometers awayMagma—the molten rock that nourishes
volcanoes—can lurk in underground pock-
ets surprisingly far from where it emerges,
new research shows. This means the
instruments placed on a volcano’s flanks
might fail to pick up signs of moving mag-
ma that can signal an impending eruption.
University of Oregon volcanologist Allan
Lerner and his colleagues focused on 56
volcanoes in subduction zones (geologically
active areas where one tectonic plate is div-
ing under another) on five continents for a
new paper, published in July in Geophysical
Research Letters.Compiling volcano data
from other studies, the team estimated the
center of each volcano’s magma reservoir
and compared it with the estimated center
of the volcano’s aboveground portion. The
reservoirs had been found through process-
es such as measuring the earth’s surface
moving up or down and tracing how the
planet’s crust conducts electricity.
The researchers calculated that rough-
ly one third of volcanoes were more than
four kilometers away from their magma
reservoirs. Five volcanoes, including
two in Japan, two in Indonesia and one
in Mexico, had offsets of more than
10 kilometers. “It was a surprise,” Lerner
says, because a long-standing tenet of
volcanology is that magma reservoirs arelocated directly underneath volcanoes.
Offset magma reservoirs have been
reported before, but the researchers say
their investigation is the first to focus on
anensemble of volcanoes. Thanks to their
large sample size, Lerner and his collabo-
rators were also able to demonstrate cor-
relations. They showed that smaller volca-
noes tended to be farther from their mag-
ma reservoirs than larger volcanoes. This
makes sense, the team suggests, because
geologic structures such as fault lines
essentially create an underground obstacle
course for magma. The large quantities
of magma that feed big volcanoes carry
enough heat to blow straight through such
natural boundaries, but the smaller reser-
voirs associated with smaller volcanoes
must forge convoluted paths to the sur-
face. “In small volcanoes, the magma that
ascends is kind of at the mercy of preexist-
ing crustal structures,” Lernersays.
These results have implications for how
volcanoes are monitored. Researchers
usually aim to place ground-based instru-
ments on or near a volcano, says Diana
Roman, a volcanologist at the Carnegie
Institution for Science, who was not
involved in the research. But this new study
indicates that such a strategy might not be
best. “This tells us we should be looking
farther afield, especially for volcanoes with
relatively small edifices,” Roman says.
Studying more volcanoes, including
those not in subduction zones, would be
valuable to see if these same trends persist,
Lerner says: “A very clear next direction
would be to expand this study to look at
volcanoes in other tectonic settings.”
—Katherine KorneiSouth Sister volcano in Oregon
has an offset magma reservoir.20 Scientific American, October 2020ALAMYADVANCES
G E O L O G YMagma
Far Afield
One third of volcanoes may have
molten reservoirs kilometers awayMagma—the molten rock that nourishes
volcanoes—can lurk in underground pock-
ets surprisingly far from where it emerges,
new research shows. This means the
instruments placed on a volcano’s flanks
might fail to pick up signs of moving mag-
ma that can signal an impending eruption.
University of Oregon volcanologist Allan
Lerner and his colleagues focused on 56
volcanoes in subduction zones (geologically
active areas where one tectonic plate is div-
ing under another) on five continents for a
new paper, published in July in Geophysical
Research Letters.Compiling volcano data
from other studies, the team estimated the
center of each volcano’s magma reservoir
and compared it with the estimated center
of the volcano’s aboveground portion. The
reservoirs had been found through process-
es such as measuring the earth’s surface
moving up or down and tracing how the
planet’s crust conducts electricity.
The researchers calculated that rough-
ly one third of volcanoes were more than
four kilometers away from their magma
reservoirs. Five volcanoes, including
two in Japan, two in Indonesia and one
in Mexico, had offsets of more than
10 kilometers. “It was a surprise,” Lerner
says, because a long-standing tenet of
volcanology is that magma reservoirs arelocated directly underneath volcanoes.
Offset magma reservoirs have been
reported before, but the researchers say
their investigation is the first to focus on
anensemble of volcanoes. Thanks to their
large sample size, Lerner and his collabo-
rators were also able to demonstrate cor-
relations. They showed that smaller volca-
noes tended to be farther from their mag-
ma reservoirs than larger volcanoes. This
makes sense, the team suggests, because
geologic structures such as fault lines
essentially create an underground obstacle
course for magma. The large quantities
of magma that feed big volcanoes carry
enough heat to blow straight through such
natural boundaries, but the smaller reser-
voirs associated with smaller volcanoes
must forge convoluted paths to the sur-
face. “In small volcanoes, the magma that
ascends is kind of at the mercy of preexist-
ing crustal structures,” Lernersays.
These results have implications for how
volcanoes are monitored. Researchers
usually aim to place ground-based instru-
ments on or near a volcano, says Diana
Roman, a volcanologist at the Carnegie
Institution for Science, who was not
involved in the research. But this new study
indicates that such a strategy might not be
best. “This tells us we should be looking
farther afield, especially for volcanoes with
relatively small edifices,” Roman says.
Studying more volcanoes, including
those not in subduction zones, would be
valuable to see if these same trends persist,
Lerner says: “A very clear next direction
would be to expand this study to look at
volcanoes in other tectonic settings.”
—Katherine KorneiSouth Sister volcano in Oregon
has an offset magma reservoir.sad1020Adva3p.indd 20 8/20/20 5:27 PM
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