There was renewed volcanic and seismic activity at San Cristóbal during the week. During mid-August a gradual increase in seismic tremor and long-period earthquakes began and the amount of tremor peaked during the night of 11 August. The same night INETER personnel heard rumbling emanate from the volcano. Seismicity began to decrease on 12 August and increased again the night of 14 August, reaching the same level detected on 11 August. On 14 August incandescence was visible in the crater for the first time during the current episode. INETER stated that the lava lake in the crater illuminated gas and clouds above the summit crater. Seismic tremor gradually decreased until approximately 1400 on 17 August when strong seismic activity began again. Fumarolic activity increased during the current episode and small lagoons within the crater had dried.

Geological Summary. 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.

Source: Instituto Nicaragüense de Estudios Territoriales (INETER)