What’s happening beneath Mount St. Helens? Scientists find major magma-storage zone underground
The findings, along with later studies using the same dataset, point to a major magma-storage zone in the upper crust, roughly 4 to 15 kilometres beneath Mount St. Helens.
- Aug 28, 2026,
- Updated Aug 28, 2026 4:30 AM IST
Scientists have taken a detailed look beneath Mount St. Helens, using controlled explosions and thousands of seismic instruments to map the hidden structures that feed one of the United States’ most closely studied volcanoes, according to a report by The Times of India.
The effort was part of the Imaging Magma Under St. Helens (iMUSH) project, an ambitious 2014 experiment designed to reveal how magma is stored and moves beneath the volcano. Instead of relying only on natural earthquakes, researchers created their own seismic signals and tracked how those waves travelled through the Earth.
The findings, along with later studies using the same dataset, point to a major magma-storage zone in the upper crust, roughly 4 to 15 kilometres beneath Mount St. Helens. Scientists estimate that parts of this zone contain about 10% to 12% partial melt.
Explosions used to probe the volcano
In late July and early August 2014, a field team of about 70 people carried out 23 controlled explosions at different distances from Mount St. Helens. The blasts were not meant to simulate an eruption. They were used as artificial seismic sources, sending waves through the ground that could be recorded by instruments spread across the region.
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Seismic waves move at different speeds depending on the material they pass through. By comparing the arrival times of the waves at different recording stations, scientists can build a picture of the rock structures beneath the surface.
The scale of the operation was unusually large. Researchers deployed roughly 800 to 1,000 Reftek seismic recorders along each of two major profiles, while another 1,600 to 1,800 instruments were placed in wider arrays around the volcano.
Closer to the summit, about 300 additional instruments and 920 nodal seismic units were positioned along trails within roughly 7.5 kilometres of the volcano. More than a dozen large arrays were also set up to record natural earthquakes.
Together, the network captured approximately 80,000 seismic traces from the 23 controlled shots.
Mapping the volcano at different depths
The seismic network was designed to examine Mount St. Helens from multiple directions and at different scales.
Two long seismic profiles stretched as far as 150 kilometres from the volcano. These were used to study structures extending from the upper crust down towards the Moho, the boundary between Earth's crust and mantle.
For a closer look at shallower structures, researchers placed two rings of controlled shots roughly 15 and 30 kilometres from the summit. Additional shots were positioned as far as 50 to 80 kilometres away to help investigate deeper sections of the crust.
This approach gave researchers a much more detailed picture than could have been obtained from a limited number of naturally occurring earthquakes.
A magma zone beneath the volcano
One of the key findings from seismic studies using the iMUSH data was a low seismic velocity zone between roughly 4 and 15 kilometres below Mount St. Helens.
Seismic waves travel more slowly through this region than through the surrounding rock. Such low velocities can be associated with hot, fractured or partially molten material, making the zone an important indicator of magma storage.
A 2023 presentation to the Seismological Society of America described the upper-crustal low velocity zone as the primary magma reservoir, with estimates suggesting it may contain roughly 10% to 12% partial melt.
That does not mean the volcano sits above a huge underground pool of liquid magma. A magma reservoir is more accurately understood as a complex mixture of molten material, crystals and surrounding rock, with much of it potentially existing in a partially molten state.
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More than a single magma chamber
The seismic studies also suggest that Mount St. Helens has a complicated magmatic plumbing system rather than a simple pipe connected to one large chamber.
Later receiver-function studies based on iMUSH data identified changes in seismic properties across the crust. Along with evidence linked to the shallow magma reservoir, researchers detected unusual high-velocity regions deeper underground.
These deeper features have been interpreted in different ways. One possibility is that they represent accumulated crystallised magma, known as magmatic cumulates. Other types of high-velocity geological material could also explain the observations.
Scientists also examined properties of seismic waves, including the ratio between P-wave and S-wave velocities, to understand variations within the crust and gather more clues about magma-related structures.
Why the underground picture matters
Mount St. Helens has a history of powerful volcanic activity, most notably the catastrophic 1980 eruption. Understanding where magma is stored and how it moves through the crust can help scientists better understand the processes that influence volcanic behaviour.
The 2014 iMUSH experiment was valuable because it allowed researchers to create controlled seismic signals and track them through the volcano's interior using thousands of instruments.
The resulting data did not reveal one simple underground chamber. Instead, they provided evidence of a complex magmatic system extending through the crust, including a major upper-crustal magma-storage zone roughly 4 to 15 kilometres beneath Mount St. Helens.
For researchers studying active volcanoes, that underground map offers an important piece of the puzzle, showing how magma may be stored, crystallised and transported beneath the surface.
Scientists have taken a detailed look beneath Mount St. Helens, using controlled explosions and thousands of seismic instruments to map the hidden structures that feed one of the United States’ most closely studied volcanoes, according to a report by The Times of India.
The effort was part of the Imaging Magma Under St. Helens (iMUSH) project, an ambitious 2014 experiment designed to reveal how magma is stored and moves beneath the volcano. Instead of relying only on natural earthquakes, researchers created their own seismic signals and tracked how those waves travelled through the Earth.
The findings, along with later studies using the same dataset, point to a major magma-storage zone in the upper crust, roughly 4 to 15 kilometres beneath Mount St. Helens. Scientists estimate that parts of this zone contain about 10% to 12% partial melt.
Explosions used to probe the volcano
In late July and early August 2014, a field team of about 70 people carried out 23 controlled explosions at different distances from Mount St. Helens. The blasts were not meant to simulate an eruption. They were used as artificial seismic sources, sending waves through the ground that could be recorded by instruments spread across the region.
Don't Miss: Moderna's cancer vaccine cuts melanoma recurrence risk in early trial: What we know
Seismic waves move at different speeds depending on the material they pass through. By comparing the arrival times of the waves at different recording stations, scientists can build a picture of the rock structures beneath the surface.
The scale of the operation was unusually large. Researchers deployed roughly 800 to 1,000 Reftek seismic recorders along each of two major profiles, while another 1,600 to 1,800 instruments were placed in wider arrays around the volcano.
Closer to the summit, about 300 additional instruments and 920 nodal seismic units were positioned along trails within roughly 7.5 kilometres of the volcano. More than a dozen large arrays were also set up to record natural earthquakes.
Together, the network captured approximately 80,000 seismic traces from the 23 controlled shots.
Mapping the volcano at different depths
The seismic network was designed to examine Mount St. Helens from multiple directions and at different scales.
Two long seismic profiles stretched as far as 150 kilometres from the volcano. These were used to study structures extending from the upper crust down towards the Moho, the boundary between Earth's crust and mantle.
For a closer look at shallower structures, researchers placed two rings of controlled shots roughly 15 and 30 kilometres from the summit. Additional shots were positioned as far as 50 to 80 kilometres away to help investigate deeper sections of the crust.
This approach gave researchers a much more detailed picture than could have been obtained from a limited number of naturally occurring earthquakes.
A magma zone beneath the volcano
One of the key findings from seismic studies using the iMUSH data was a low seismic velocity zone between roughly 4 and 15 kilometres below Mount St. Helens.
Seismic waves travel more slowly through this region than through the surrounding rock. Such low velocities can be associated with hot, fractured or partially molten material, making the zone an important indicator of magma storage.
A 2023 presentation to the Seismological Society of America described the upper-crustal low velocity zone as the primary magma reservoir, with estimates suggesting it may contain roughly 10% to 12% partial melt.
That does not mean the volcano sits above a huge underground pool of liquid magma. A magma reservoir is more accurately understood as a complex mixture of molten material, crystals and surrounding rock, with much of it potentially existing in a partially molten state.
Must Read: Expired food, pests, foul smell: Posh Delhi hotels booked for BRICS summit under FSSAI lens
More than a single magma chamber
The seismic studies also suggest that Mount St. Helens has a complicated magmatic plumbing system rather than a simple pipe connected to one large chamber.
Later receiver-function studies based on iMUSH data identified changes in seismic properties across the crust. Along with evidence linked to the shallow magma reservoir, researchers detected unusual high-velocity regions deeper underground.
These deeper features have been interpreted in different ways. One possibility is that they represent accumulated crystallised magma, known as magmatic cumulates. Other types of high-velocity geological material could also explain the observations.
Scientists also examined properties of seismic waves, including the ratio between P-wave and S-wave velocities, to understand variations within the crust and gather more clues about magma-related structures.
Why the underground picture matters
Mount St. Helens has a history of powerful volcanic activity, most notably the catastrophic 1980 eruption. Understanding where magma is stored and how it moves through the crust can help scientists better understand the processes that influence volcanic behaviour.
The 2014 iMUSH experiment was valuable because it allowed researchers to create controlled seismic signals and track them through the volcano's interior using thousands of instruments.
The resulting data did not reveal one simple underground chamber. Instead, they provided evidence of a complex magmatic system extending through the crust, including a major upper-crustal magma-storage zone roughly 4 to 15 kilometres beneath Mount St. Helens.
For researchers studying active volcanoes, that underground map offers an important piece of the puzzle, showing how magma may be stored, crystallised and transported beneath the surface.