Skip to main content
Volcanoes release CO₂ not only through visible plumes but also diffusely through soils and fractures. These diffuse emissions can account for a significant portion of a volcano’s total carbon output, yet they are invisible to the eye and undetectable by plume-based methods such as scanning DOAS or MultiGAS. Measuring soil CO₂ concentrations captures this hidden degassing signal close to its source, before it disperses into the atmosphere.

​
How it works

The AVERT deployments use Vaisala CARBOCAP GMP343 non-dispersive infrared (NDIR) probes equipped with a soil adapter. The sensor measures how much infrared light is absorbed by CO₂ in the soil air space — higher CO₂ concentrations absorb more infrared energy. The instrument includes compensation for temperature variations and static compensation for humidity and pressure, providing reliable measurements in the challenging conditions found near volcanic vents.
Because soil CO₂ probes measure gas concentrations at shallow depth before atmospheric dilution, they can detect subtle changes in degassing that surface-level instruments might miss.

​
AVERT deployments

Soil CO₂ probes were deployed at two AVERT volcanoes as novel monitoring tools — the first continuous soil CO₂ instruments on any Alaskan or Costa Rican volcano:
  • Okmok (OKCE): A single GMP343 probe was installed inside the caldera, where diffuse degassing occurs across the caldera floor rather than solely from discrete vents. There is now a 3+ year continuous record that can be compared to seismicity and inflation at Okmok.
  • Poas (VPPC): A single GMP343 probe was installed at the crater rim. The CO₂ time series proved particularly valuable — concentrations rose in tandem with seismic tremor and increased prior to the start of explosive activity within the central crater during the January–April 2025 eruptive episode.
Soil CO₂ data are interpreted alongside co-located soil temperature and moisture measurements where available, which help distinguish gas-driven variations from environmental effects.