Volcanic tremor began to increase at San Cristóbal on 28 May, reaching a peak around noon the next day. The summit of the volcano was not visible, but satellite imagery from the Centro de Vigilancia de Ceniza Volcánica revealed that ash was emitted from the volcano. After the 29th, the amount of tremor decreased. Incandescence was visible at the crater rim on 1 June. By 3 June tremor was still relatively high.

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.

Sources: La Prensa (Nicaragua), Instituto Nicaragüense de Estudios Territoriales (INETER)