Hecates Tholus is 180 km across and 4.8 km high. The slopes of the volcano are heavily dissected with channels, suggesting that the volcano is composed of easily erodible material such as volcanic ash. The origin of the channels is unknown; they have been atrributed to lava, ash flows, or even water from snow or rainfall. Albor Tholus, the southernmost of the Elysium volcanoes, is 150 km in diameter and 4.1 km high. Its slopes are smoother and less heavily cratered than the slopes of the other Elysium volcanoes.