The existence of a cirque on the northwestern slope has been postulated. It was once believed that Llullaillaco had experienced three large glaciations, but the moraines are actually mudflow deposits. However, during the Pleistocene glaciers reached down to altitude on the northwestern slope. Lava flows have overrun some of the glaciated surfaces and it is possible that lava flows induced the melting of glaciers. A number of glacial landforms elsewhere were destroyed by mudflows during the time of Llullaillaco's last activity. Llullaillaco may not have been glaciated at all during the Pleistocene.