[8] Large normal faults cut across and completely penetrate the volcano, dividing the edifice into several major blocks, or sectors.

In profile, Tharsis Tholus is dome-shaped (convex upward),[9] with flank slopes ranging from less than 1° near the summit to up to 16° at the base.

The base of the volcano is buried by young (Amazonian-aged) lava flows presumably from the Tharsis Montes, so the true size of the edifice cannot be accurately determined.

[8] The mantle material obscures the underlying bedrock except in areas with steep slopes, such as along the caldera's upper walls.

[6] CRISM data from MRO show that lava exposed on the caldera scarp is composed of high- and low-calcium pyroxenes.

Some researchers[6][8][13] have compared the deformation on the flanks of Tharsis Tholus to "sector collapse" observed at Mauna Loa in Hawaii and other terrestrial volcanoes.

[d] In addition to the normal faults, a system of narrow, parallel grabens cut across large parts of the volcano.

In addition, a fissure-type eruption that formed a small stratocone is present near the south flank of the main volcano.

[6][14] Crater counting shows that the oldest parts of Tharsis Tholus formed around 3.82 billion years ago (Gya) in the late Noachian Period.

A fissure eruption on the south flank produced a lava flow around 196 million years ago (Late Amazonian Period).

The fissure-type eruption at the south flank of Tharsis Tholus is relatively young, so it may indicate that future volcanic activity is still possible at the mountain.