Alitar is constructed on Miocene-Pliocene La Pacana and Atana ignimbrite. The volcano is composed from andesites and dacites of Pliocene-Pleistocene age. A 500 metres (1,600 ft) wide, 50 metres (160 ft) deep maar lies at the southwest foot of the volcano. Fumarolic activity occurs both in the northern sector of the maar and another area 400 metres (1,300 ft) northwest of it. 200 metres (660 ft) west of the maar a hydrothermal well system comprising six pools and gas discharges is located in a creek.