We have collected 14 water and gas samples from 9 thermal springs and gas vents near Nevado del Ruiz volcano, Colombia. The 3He/4He and 4He/20Ne ratios vary significantly from 0.98 Ratm (where Ratm is the atmospheric 3He/4He ratio of 1.4 × 10-6) to 6.30 Ratm, and from 0.37 to 7.0, respectively. The 3He/4He ratio (corrected for air contamination) decreases with increasing distance from the central crater of the volcano to the sampling site. The trend is very similar to that observed at Ontake volcano, Japan. A hydrodynamic porous-media dispersion model can explain the 3He/4He trend. The temporal variations in the 3He/4He ratio at four sites provide useful information on the apparent velocity of the magmatic fluid flow brought on by a volcanic eruption. The estimated value of several tens m day-1 agrees well with the inferred velocity of flow in Oshima volcano, Japan and is comparable to the largest rate of groundwater movement in a deep sedimentary basin.
ASJC Scopus subject areas
- Geochemistry and Petrology