Report on San Cristobal (Nicaragua) — March 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 3 (March 1981)
Managing Editor: Lindsay McClelland.
San Cristobal (Nicaragua) Emissions of SO2 increase by an order of magnitude; high seismicity; incandescence
Please cite this report as:
Global Volcanism Program, 1981. Report on San Cristobal (Nicaragua). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 6:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198103-344020.
12.702°N, 87.004°W; summit elev. 1745 m
All times are local (unless otherwise noted)
"A trend of decreasing SO2 emissions had been evident since the small ash eruptions of March 1976. However, San Cristóbal has suddenly reversed this trend, after being in a heightened state of seismic activity since August 1980. In late February, SO2 output increased by approximately an order of magnitude to the several thousand t/d level of the mid-1970's. Flights over the crater in mid-February and mid-March showed evidence of considerable recent slumping in the crater formed by the 1976 eruptions, especially on the N and NW walls. Fumarolic activity was evident all over the crater but was most concentrated in the S and SE margins of the floor and in the lower parts of the walls. No new fumaroles or fissures were observed outside the 1976 crater. Night observation revealed extensive incandescence over much of the crater, even more than that observed in December at Momotombo. High gas concentrations and unstable footing prevented measurement of any fumarole temperatures. Seismic activity continued at high levels, with almost continuous harmonic tremor and at least one earthquake with magnitude greater than 2 (which occurred one week before the elevated SO2 emission was detected)."
Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.
Information Contacts: R. Stoiber and S. Williams, Dartmouth College; D. de Jerez, IRENA; D. Fajardo B., Instituto de Investigaciones Sísmicas.