Mombacho is a stratovolcano on the shores of Lake Nicaragua that has undergone edifice collapse on several occasions. Two horseshoe-shaped craters cut the summit on the NE and south flanks, modifying the profile of the volcano. The NE-flank scarp, whose NE wall forms the left skyline, was the source of a large debris avalanche that produced an arcuate peninsula and the Las Isletas chain of islands in Lake Nicaragua. The only reported historical activity was in 1570, when a debris avalanche destroyed a village on the south side of the volcano.
Las Isletas, a group of islands NE of Mombacho volcano, were created by a large Holocene debris avalanche from Mombacho that swept into Lake Nicaragua. The avalanche traveled at least 12 km from Mombacho. The hummocky debris from the avalanche created an arcuate peninsula that extends into the lake as well as hundreds of small islands. This morphology is common where debris avalanches enter shallow bodies of water.