Note: This caption refers to the image versions labeled "NASA's Earth Observatory web site".
The Chiltepe Peninsula, highlighted in this astronaut photograph from the International Space Station, extends into Lake Managua in west-central Nicaragua. The peninsula is formed from part of a large ignimbrite shield, a geologic structure created by deposition of primarily low density materials (such as pumice) ejected during violent, explosive eruptive activity. Ignimbrite deposits are most commonly emplaced during large pyroclastic flows - gravity-driven mixtures of rock, ash, and volcanic gases that can cover 100s of kilometers at speeds of 100s of kilometers per hour - with ignimbrite shields formed over geologic time by successive flows.
The Apoyeque caldera, filled with a 2.8 km wide and 400 meter deep lake, dominates the center of the peninsula. Geological evidence indicates that Apoyeque last erupted around 50 BCE (plus or minus 100 years). The Laguna Xiloa maar - a volcanic crater formed by the explosive interaction of magma and groundwater - is located immediately to the southeast of Apoyeque and is also filled with a lake. Laguna Xiloa last erupted approximately 6100 years ago.
More recently, a swarm of small earthquakes was detected near Apoyeque in 2012. These seismic swarms, when detected in volcanically active areas, may indicate movement of magma prior to an eruption. The capital city of Managua, not visible in the image, is located approximately 15 kilometers to the southeast of Apoyeque, while the town of Bosques de Xiloa is considerably closer (approximately 4 km).