page_title: Mountains of Io
section_title: Observations
hierarchical_section_title: Mountains of Io / Observations
caption_attribution_description: English: This figure show one of Io's morphological type-Mesa. This example is Tvashtar Mesa. It has a flat top and a sharp boundary.
context_page_description: Mountains are widely distributed across the surface of Io, the innermost large moon of Jupiter. There are about 115 named mountains; the average length is 157 km and the average height is 6,300 m. The longest is 570 km, and the highest is Boösaule Montes, at 17,500 metres, taller than any mountain on Earth. Ionian mountains often appear as large, isolated structures; no global tectonic pattern is evident, unlike on Earth, where plate tectonics is dominant.
  Io is exceptional for the strong tidal heating it undergoes, caused by the eccentricity of its orbit in conjunction with the proximity and great mass of Jupiter. This leads to widespread and intensive volcanism.
  Most volcanoes on Io have little relief; those that can be considered mountains are generally smaller than the mountains formed by tectonic processes, averaging only 1,000 to 2,000 metres in height and 40 to 60 kilometres in width. Several geodynamic models of Io exist but the tectonic mountain-building process is still obscure and debatable. However, it is thought to be related to stresses caused by the rapid volcanic resurfacing of the body.
context_section_description: To explore the origin of Io's mountains, classification of morphological types and description of morphological features are necessary.
  Morphological types
  Four morphological types of mountains have been identified.
  Mesa: a mountain with flat top and relatively smooth surface. It may be difficult to distinguish mesas from eroded layered plains. Ethiopia Planum is a good example of this morphological type. Eleven mountains on Io are classified as mesas.
  Plateau: an elevated plain with a rugged surface. There is no steep or prominent peak on plateau. Iopolis Planum is a good example of this type. About 46% of Ionian mountains belong to this morphological type.
  Ridge: an elevated structure dominated by one or more linear or arcuate rises. 28 (24%) mountains on Io have been cataloged into this type.
  Massif: an elevated structure dominated by rugged or complex surface and has one or more peaks. Boösaule Montes and Tohil Mons are good examples.
  Common features
  Several common features of Ionian mountains have been summarized.
  Basal scarps: basal scarps always appear as an abrupt boundary of Ionian mountains that separate mountains from volcanic plains. Most Ionian mountains are observed to have this feature. The basal scarps are ten to a few hundred meters high.  Sometimes, the scarp is resolved in high-resolution images as the margin of a debris apron. An example is Iopolis Planum.
  Tilted block: thrust faults have been interpreted to bound tilted blocks on Io. Tilted blocks have a polygonal shape and curved crests. One example is Euboea Montes. A terrestrial analogy is the Black Hills of South Dakota.
  Mass wasting: several types of mass movement deposits have been observed adjacent to Ionian mountains. Downslope movements of blocks have been noted in at least one place, the Euboea Montes. Fan-shaped deposits resembling debris aprons are found at the base of steep slopes. The ridged or crenulated surfaces of some mountains like northern Hi'iaka Montes may be formed by downslope creep of layered rock.
  Layered crust: the upper Ionian crust may be layered, as suggested by flowing observations: mountain uplifted 17,000 m (56,000 ft) and exposed crust section at Euboea Montes, different colored units exposed on Haemus Mons, a ridged unit atop northern Hi'iaka Montes, and striations on mountains such as Haemus Mons and Tohil Mons.
caption: Mesa on Io. This example is Tvashtar Mesa. It has a very flat top and a sharp boundary.
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