> ## Documentation Index
> Fetch the complete documentation index at: https://data.avert.ldeo.columbia.edu/llms.txt
> Use this file to discover all available pages before exploring further.

# Background

> Measuring diffuse CO₂ degassing through volcanic soils

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.

<Tip>
  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.
</Tip>

## 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.

<Note>
  Soil CO₂ data are interpreted alongside co-located soil temperature and
  moisture measurements where available, which help distinguish gas-driven
  variations from environmental effects.
</Note>