The name is commonly used in a broad sense to represent a continent-sized region of anomalously elevated terrain centered just south of the equator around longitude 265°E.

The bulge is slightly elongated in the north-south direction, running from the northern flanks of Alba Mons (about 55°N) to the southern base of the Thaumasia highlands (about 43°S).

[12][13] The oldest part of the northern rise consists of a broad topographic ridge that corresponds to the highly fractured terrain of Ceraunius Fossae.

Its western boundary is roughly defined by the high lava plains of Daedalia Planum, which slope gently to the southwest into the Memnonia and Terra Sirenum regions.

[19] These boundaries enclose a broad high plateau and shallow interior basin that include Syria, Sinai, and Solis Plana (see list of plains on Mars).

The highest plateau elevations on the Tharsis bulge occur in northern Syria Planum, western Noctis Labyrinthus, and the plains east of Arsia Mons.

[15] The lava plains slope gently to the east where they overlap and embay the older (Hesperian-aged) terrain of Echus Chasma and western Tempe Terra.

The NSVs may be relics from catastrophic floods of water, similar to the huge outflow channels that empty into Chryse Planitia, east of Tharsis.

Tharsis is commonly called a volcano-tectonic province, meaning that it is the product of volcanism and associated tectonic processes that have caused extensive crustal deformation.

The hot spot produces voluminous quantities of magma in the lower crust that is released to the surface as highly fluid, basaltic lava.

If the magma migrates through vertical fractures it produces swarms of dikes that may be expressed at the surface as long, linear cracks (fossae) and crater chains (catenae).

[23][24] The enormous sagging weight of Tharsis has generated tremendous stresses in the crust, producing a broad trough around the region[25] and an array of radial fractures emanating from the center of the bulge that stretches halfway across the planet.

[26] Geologic evidence, such as the flow direction of ancient valley networks around Tharsis, indicates that the bulge was largely in place by the end of the Noachian Period,[25] some 3.7 billion years ago.

Exhalations from Tharsis and other volcanic centers on the planet are likely responsible for an early period of Martian time (the Theiikian[29]) when sulfuric acid weathering produced abundant hydrated sulfate minerals such as kieserite and gypsum.

A more recent study reported in Nature agreed with the polar wander, but the authors thought the eruptions at Tharsis happened at a slightly different time.

[36] Recent work has attempted to refine the definition of a volcano to incorporate geologic features of widely different shapes, sizes, and compositions throughout the Solar System.

Mathematical analysis shows that volcanic spreading operates on volcanoes at a wide range of scales and is theoretically similar to the larger-scale rifting that occurs at mid-ocean ridges (divergent plate boundaries).

Mount Etna is a complex spreading volcano that is characterized by three main structural features: a volcanic rift system that crosses the summit in a north-northeast direction; a peripheral compression belt (thrust front) surrounding the base of the volcano; and an east-northeast trending system of transtensional (oblique normal) faults that connect the summit rift to the peripheral thrust front.

Unlike on Earth, where the rifting of plates produces a corresponding subduction zone, the thick lithosphere of Mars is unable to descend into the mantle.