The scenic 8 x 11 km Ilopango caldera, filled by one of El Salvador's largest lakes, has a scalloped 150-500 m high rim. The caldera, which lies immediately east of the capital city of San Salvador, is strongly controlled by regional faults of the central Salvador graben. Four major dacitic-rhyolitic explosive eruptions during the late Pleistocene and Holocene produced extensive pyroclastic-flow and pyroclastic-fall deposits that blanket much of El Salvador. The latest collapse of Ilopango caldera resulted from the massive 5th century AD Terra Blanca Joven (TBJ) eruption, which produced widespread pyroclastic flows and devastated early Mayan cities. Post-caldera eruptions formed a series of glassy dacitic and andesitic lava domes within the lake and near its shore. The Islas Quemadas, a group of low islets in the center of the lake that mark the summit of a largely submerged lava dome, were formed in 1879-80 during the only historical eruption of Ilopango.