Between 14 June and 11 July, personnel from PIRPSEV, CNRS, and the volcano observation section of IPG sampled medium-to-high temperature gases from Momotombo (table 1). Maximum gas temperatures measured were 640°C.

Table 1. Analytical mean of four mid-1981 gas samples (dry, HCl excluded) from Momotombo. Courtesy of H. DeLorme and J. Cheminée.

Geological Summary. Momotombo is a young stratovolcano that rises prominently above the NW shore of Lake Managua, forming one of Nicaragua's most familiar landmarks. Momotombo began growing about 4500 years ago at the SE end of the Marrabios Range and consists of a somma from an older edifice that is surmounted by a symmetrical younger cone with a 150 x 250 m wide summit crater. Young lava flows extend down the NW flank into the 4-km-wide Monte Galán caldera. The youthful cone of Momotombito forms an island offshore in Lake Managua. Momotombo has a long record of Strombolian eruptions, punctuated by occasional stronger explosive activity. The latest eruption, in 1905, produced a lava flow that traveled from the summit to the lower NE base. A small black plume was seen above the crater after a 10 April 1996 earthquake, but later observations noted no significant changes in the crater. A major geothermal field is located on the south flank.

Information Contacts: H. DeLorme, Univ. de Paris; J. Cheminée, IPG, Paris.