One plume

Tharsis is one standing volcanic rise.

Mars

Mars built one volcanic rise. Earth tore its piles apart.

Tharsis is the largest volcanic province in the solar system. The rise is thousands of kilometres across and about 10 kilometres high. It covers as much as a quarter of Mars. On top of it sit twelve large shields. Three of them — Arsia, Pavonis, and Ascraeus — stand in a southwest-to-northeast line, peaks about 700 kilometres apart. Olympus Mons sits off the western edge: about 600 kilometres across and 21 to 22 kilometres high.

Earth has the same engine. It does not have the same standing pile. A plume under a lid that does not move builds one mountain. A plume under a lid that walks builds a chain, a flood-basalt province, or a drowned plateau. Those are what the same engine leaves when the ground moves. They are not a worn-down Tharsis.

This site reads Io through Mars as consecutive stages of one kind of planet, with living Earth as the present chapter. Tharsis is what a late stagnant lid can load. The missions do not prove the handoff.

The ordinary view

The usual reading is a long-lived mantle plume under a stagnant lid. Most of the mass was in place by the end of the Noachian, about 3.7 billion years ago. Late flows continued. The load of the rise flexed the crust and helped open Valles Marineris. The three Montes are evenly spaced on one azimuth. That line is unlikely to be an accident.

Olympus grew so large because the crust did not drift off the source. Gravity on Mars is lower than on Earth, so a pile can stand higher before the rock fails. Mauna Loa is the comparison people reach for. It is about 120 kilometres across. Olympus is in another class because the plate never left.

Figure 1. Mars topography from MOLA. Tharsis is the high western rise: Olympus Mons, the three Tharsis Montes in a line, Alba Mons to the north, Valles Marineris cutting east. Elysium is the smaller rise on the right. Image: NASA / JPL / GSFC.

What Earth shows

A typical continental large igneous province is about a million square kilometres and a million cubic kilometres. The Siberian Traps, Earth’s largest continental flood basalt still in one piece, run a few million cubic kilometres. Ontong Java, the largest surviving oceanic plateau, is tens of millions. Tharsis volume sits above both. Elysium, Mars’s second rise, is the one that falls in Earth’s LIP size class.

Table 1. Tharsis is not an Earth flood-basalt province scaled up by a little. It is a rise that still covers a quarter of its world.
Pile	Scale	What it is
Tharsis	Quarter of Mars; above Earth’s LIPs	One standing rise on a lid that did not walk
Elysium	Earth LIP class	Mars’s second rise
Siberian Traps	A few million km³	Largest continental flood basalt still in one piece
Ontong Java	Tens of millions km³	Largest surviving oceanic plateau
Mauna Loa	~120 km across	A shield on a walking plate — not Olympus

What would move a clock

Table 2. An age-progressive chain would put a walking plate back on the table. Late flows on the same rise would not.
Row	What would move it	What would not
One standing plume	An age-progressive shield chain across Tharsis	Late flows on the same rise
Not a worn-down Earth LIP	Tharsis volume shown inside Siberian Traps class	Elysium staying in Earth’s LIP class
Stagnant-lid engine	Proof the crust walked off the source while Olympus grew	Lower gravity as part of why the pile stands

On this reading

This site reads Mars as the last window before living Earth. A lid that does not walk can keep one plume in one place and grow a load the size of a small continent. Earth later tears those piles apart because the lid learned to break. Equal windows on this site are a modeling choice. They do not move a world.

What would weaken this

An age-progressive shield chain across Tharsis would put a walking plate back on the table. A Tharsis volume inside the Siberian Traps class would take the unmatched-pile row off the table. Neither result would prove a handoff.

What this page holds

Mars built one volcanic rise. Earth tore its piles apart. This site reads that as lid behaviour on consecutive stages. The standing pile is the measurement. The missions do not prove the handoff.

Sources

MOLA topography; NASA / JPL / GSFC global map of Tharsis, Olympus, and Elysium.

Tharsis as a long-lived plume under a stagnant lid; most mass by the late Noachian, late flows continuing.

Earth LIP compilations: Siberian Traps; Ontong Java. Mauna Loa as the walking-plate shield people reach for.

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