The northern flank of Hualca Hualca underwent a large sector collapse between 1.36 and 0.61 million years ago, opening up a collapse amphitheatre and forming a lake in the Colca valley which later catastrophically failed. This lake has left lacustrine deposits in the Colca Valley. Eruptions within the collapse amphitheatre generated lava flows which then formed volcanic dams in the Colca Valley. Lava domes and pyroclastic flows also originated within the collapse scar. Earthquakes and hydrothermal alteration probably caused the onset of the collapse event.