Maipo is located within the Diamante caldera, a feature measuring 15 km by 20 km that is about half a million years old. It rises about 1,900 m (6,230 ft) above the floor of the caldera. Immediately to the east of the peak, on the eastern side of the caldera floor, is Laguna del Diamante, a lake that formed when lava flows blocked drainage channels from the caldera in 1826. The Diamante Caldera erupted of tephra, 450 ka.