Since the small phreatic explosion on 8 May, vapor emission has continued. Steaming increased slightly from some older fumaroles, probably because of recent heavy rains. As of late May, about 2-3 fairly large and a dozen small tectonic events were recorded daily. About 90% of the shocks were very shallow and most epicenters were within 3 km of the vent. Seismicity had declined somewhat by mid-June, while deformation and temperatures of nearby hot springs remained stable.

Geological Summary. Tacaná is a 4064-m-high composite stratovolcano that straddles the México/Guatemala border at the NW end of the Central American volcanic belt. The volcano rises 1800 m above deeply dissected plutonic and metamorphic terrain. Three large calderas breached to the south, and the elongated summit region is dominated by a series of lava domes intruded along a NE-SW trend. Volcanism has migrated to the SW, and a small adventive lava dome is located in the crater of the youngest volcano, San Antonio, on the upper SW flank. Viscous lava flow complexes are found on the north and south flanks, and lobate lahar deposits fill many valleys. Radial drainages on the Guatemalan side are deflected by surrounding mountains into the Pacific coastal plain on the SW side of the volcano. Historical activity has been restricted to mild phreatic eruptions, but more powerful explosive activity, including the production of pyroclastic flows, has occurred as recently as about 1950 years ago.

Information Contacts: M. Mena and S. de la Cruz Reyna, UNAM, México D.F.