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Volcanoes emit heat not only through eruptions and fumaroles but also diffusely through the ground. Changes in soil temperature can reflect variations in heat flow from depth, shifts in hydrothermal circulation, or changes in diffuse degassing pathways. Recent remote sensing studies have shown that some volcanic systems exhibit large-scale variations in the release of heat prior to eruptions, making continuous ground-based temperature measurements a valuable complement to satellite observations.

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How it works

The AVERT deployments use TEROS 12 sensors, which have three stainless-steel needles and measure three properties simultaneously:
  • Soil moisture — determined by supplying a 70 MHz oscillating wave and measuring the charge time, which depends on the dielectric permittivity (and thus water content) of the surrounding soil
  • Electrical conductivity — measured by applying an alternating current between two electrodes
  • Temperature — measured by a thermistor embedded in the middle needle
Pairs of sensors are installed at two depths (shallow and deep) to capture the vertical temperature profile. The data are digitised using Campbell Scientific CR1000 dataloggers and telemetered in near real time.
When measured together with soil CO₂, these datasets help distinguish thermal signals from purely gas-driven variations, and provide context for interpreting changes in soil gas transport.

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AVERT deployments

Soil temperature probes were deployed at Okmok volcano — the first continuous soil temperature instruments on any Alaskan volcano:
  • OKCE: A pair of TEROS 12 sensors at shallow and deep depths, co-located with a Vaisala GMP343 CO₂ probe. This site provides the most complete soil monitoring record in the AVERT network.
  • OKNC: A pair of TEROS 12 sensors at shallow and deep depths. Together with OKCE, these measurements span areas of diffuse degassing across the caldera floor, offering a fuller picture of subsurface thermal and gas processes.