Mount Erebus, the world’s southernmost active volcano, rises 3,794 metres above Antarctica’s Ross Island and sits on a section of Earth’s crust only 17 to 22 kilometres thick, roughly half the depth geologists typically expect beneath a volcano of this age and scale. Findings published in Scientific Reports in April 2026 quantify the crustal structure beneath Erebus using seismic data collected between 2016 and 2020 from four stations placed directly on the volcano. What the measurements returned was a picture of a crust under sustained geological stress, internally fractured, thermally elevated, and shot through with zones where rock behaves more like a fluid than a solid.
To understand why this matters, you need to know what the crust is doing mechanically. The crust is the outermost solid shell of the Earth, sitting above the mantle, which is the denser, hotter layer below. The boundary between the two is called the Moho, short for Mohorovicic discontinuity, a name given to the depth at which seismic waves change speed because the rock composition shifts. Beneath most stable continental regions the Moho sits around 35 to 40 kilometres down. Beneath Ross Island it sits at roughly 17 to 22 kilometres. That thinning is not random. It is the product of a stretching process called lithospheric extension that has been active in this part of Antarctica since the Jurassic period, more than 150 million years ago, through a structure called the Terror Rift, which runs directly beneath the island. Ross Sea rifting previously compressed crustal thickness from 40 kilometres to around 27 kilometres across McMurdo Sound, and the crust beneath Erebus itself sits at the thinner end of that range.
Seismologists measure crustal properties using a technique called receiver function analysis. When a distant earthquake of magnitude 6.0 or greater sends seismic waves through the Earth, those waves hit boundaries between rock layers at different depths and partially convert from one wave type to another. By recording the timing and character of those conversions at surface sensors, geophysicists can calculate how deep the boundaries are and what the rock between them looks like. The four stations on Erebus, ELHT, NAUS, CONZ, and ICEZ, recorded teleseismic events from distances between 30 and 95 degrees of arc over four years. The Moho signal arrived at between 2 and 2.5 seconds across all four stations, placing the crust-mantle boundary at a consistent shallow depth, with the measurement varying by no more than 3 kilometres between different directional segments at any single station.
The critical number the analysis returned is the Vp/Vs ratio. This is the ratio of how fast a compression wave travels through rock compared to a shear wave. Geologists use it as a direct indicator of what the rock is made of and what state it is in. Ratios between 1.60 and 1.73 are consistent with felsic rock, meaning lighter, silica-rich material like granite. Ratios between 1.74 and 1.79 indicate intermediate compositions. Ratios above 1.80 indicate mafic rock, meaning denser, iron and magnesium-rich material, the kind typical of basalt and gabbro, and also the kind associated with partial melt, meaning rock that is beginning to liquefy. Beneath Erebus the bulk crustal Vp/Vs ratio spans from 1.61 to 1.94 depending on which station and which directional segment is measured. That 0.33-point spread across a crust only 20 kilometres thick is not a measurement artefact. It is a physical signature of rock that has been chemically and thermally scrambled by millions of years of volcanic intrusion.
The variation is not uniform across the volcano. In the northwest direction from the summit, two of the four stations recorded Vp/Vs values consistently above 1.80. That matches a separately observed low-velocity seismic channel in the northwest quadrant that prior studies had imaged beneath the Erebus summit crater. A low-velocity channel is a zone where seismic waves slow down, which happens when rock is hotter than average, partially molten, or saturated with fluid. The correspondence between the elevated Vp/Vs in the northwest and the pre-existing low-velocity channel in the same direction places both measurements on the same physical structure, a region of thermally modified, mafic-dominated crust extending from somewhere in the mid-crust upward toward the active lava lake at the summit. The upper mantle velocity beneath the stations ranges from 4.2 to 4.6 kilometres per second, which is within normal bounds, but the low-velocity zones detected in earlier studies extend to around 150 kilometres depth, with a temperature anomaly in the upper mantle calculated at 200 to 300 Kelvin above background.
The CO2 chemistry of Erebus adds a separate complicating layer. The volcano is a documented CO2-rich system, with measurements of carbon dioxide emission rates directly from the persistent lava lake confirming a magma reservoir that carries elevated gas content. Carbon dioxide-saturated rock and CO2-filled fractures in the crust depress the Vp/Vs ratio, meaning some of the lower readings in the dataset, those in the 1.61 to 1.67 range recorded in the 0 to 90 degree directional segment at multiple stations, are consistent with silica-rich lithologies mixed with CO2-saturated zones rather than indicating a compositionally felsic crust. The magnetotelluric imaging of Erebus carried out in 2022 independently detected elevated electrical conductivity beneath Ross Island, which occurs when rock contains interconnected partial melt or fluid. The seismic and electromagnetic datasets were collected by different methods sensitive to different physical properties, and they converge on the same zones of anomalous subsurface behaviour beneath the volcano.
The magma pathway beneath Erebus is not a simple vertical pipe. The 2022 magnetotelluric study traced the resistivity trajectory of the magmatic system and found it shifts from a west-dipping orientation beneath the summit to a steep vertical geometry further into the interior of the crust. The new seismic data places high shear wave velocities, above 4.0 kilometres per second, in the upper crust at depths consistent with solidified mafic intrusions, which are old magma bodies that cooled in place. Below those solidified zones, the mid-crust carries lower velocities and the elevated Vp/Vs values that indicate either active partial melt or thermally modified rock not yet fully crystallised. The Moho depth itself, where it is most clearly resolved, marks the point where the resistivity trajectory shifts. That geometric change at the crust-mantle boundary is where the deepest mantle-sourced CO2, tephrophonolite, and basanite are expelled into the overlying system.
The broader regional context matters here. The Transantarctic Mountains to the west and inland carry crust up to 39 kilometres thick. Ross Island sits at the extreme thin end of the regional gradient, with crustal thickness falling from 36 to 40 kilometres under the mountains to 17 to 22 kilometres under the island, across a lateral distance measured in tens of kilometres. That gradient drives the entire volcanic system. Thin crust provides a shorter path for mantle-derived melt to reach the surface, and the active Terror Rift keeps the crust from thickening or healing. Early models of Erebus proposed a narrow vertical mantle plume directly beneath the island feeding the volcano from depth. More recent geophysical synthesis has shifted that picture. The low-velocity anomalies detected in the mantle beneath Erebus extend 250 to 300 kilometres wide and reach to at least 200 kilometres depth, far too broad for a narrow plume conduit, consistent instead with diffuse, tectonically modulated upwelling distributed across the West Antarctic Rift System rather than concentrated beneath a single point.
What this means in practical terms is that the volcanic activity at Erebus is not sustained by a single discrete heat source that could conceivably switch off or migrate. The heat supply is distributed through the rift system over hundreds of kilometres of lithosphere. The crustal architecture above it, patchy, thinned, chemically heterogeneous, and structurally controlled by faults and older intrusive bodies, acts as both a filter and a storage system for ascending melt. Magma does not rise straight up. It pools in zones of crustal weakness, reacts with existing rock, accumulates CO2 as pressure drops, and follows fault-controlled pathways that change geometry between the deep crust and the surface. The lava lake at the summit of Erebus, which has been continuously active for decades, is the surface expression of a system that operates across 20 kilometres of fractured, thermally disturbed crust and an additional 150 kilometres of anomalously hot mantle below it.
Four seismic stations currently maintain active monitoring on the volcano through the Interim Broadband Monitoring network, operating at 40 samples per second. Crustal thickness estimates from the current dataset range from 17 to 20 kilometres via velocity inversion and 18.5 to 22.1 kilometres via the stacking method, with the maximum station-to-station Moho depth difference of approximately 3 kilometres. The paper carrying these measurements remains in press at Scientific Reports as of April 2026, accepted 10 April 2026, and is under final editorial review before full publication.
Source:
Mukherjee, P., Ito, Y., Borah, K., Garcia, E. S., & Bora, D. K. (2026). Crustal Structure and Magmatic System of Mount Erebus in Antarctica constrained by Receiver Functions and Seismic Velocity Analysis. Scientific Reports. https://doi.org/10.1038/s41598-026-48866-9
