Secular variations of helium and carbon isotopes at Galeras volcano, Colombia

Yuji Sano, Toshitaka Gamo, Stanley Williams

Research output: Contribution to journalArticle

38 Scopus citations

Abstract

We have measured 3He/4He, 4He/20Ne and CO2/4He ratios, and δ13C values of CO2 in eighteen samples from crater fumaroles of Galeras volcano, Colombia, and seven samples of bubbling gases of the Pandiaco mineral spring located about 8 km east of the volcano from April 1988 to July 1995. The 3He/4He ratios of crater fumaroles, corrected for atmospheric contamination, increased significantly from 5.47 Ratm in December 1989 to 7.93 Ratm in August 1990 and reached a maximum of 8.84 Ratm in May 1992. The ratio then decreased gradually until July 1995. Overall variation of helium isotopes appears to be related to the current activity of the volcano. The 3He/4He ratios of Pandiaco mineral spring were constant between April 1988 and November 1991 and increased in April 1993, although experimental error is large. The δ13C values of CO2 of crater fumaroles show negative correlation to the helium isotopes, while those of Pandiaco are relatively constant. Based on the δ13C values and CO2/3He ratios, it is possible to estimate fractions of upper mantle carbon in these samples. Calculated mantle fractions are 3-10% in crater fumaroles, while those in Pandiaco spring are negligibly small.

Original languageEnglish (US)
Pages (from-to)255-265
Number of pages11
JournalJournal of Volcanology and Geothermal Research
Volume77
Issue number1-4
DOIs
StatePublished - May 1997

Keywords

  • Carbon isotopes
  • Galeras volcano
  • Helium isotopes
  • Volcanic gas

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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