Terrestrial Analogs to Planetary Volcanic Processes

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article. More than 50 years of solar system exploration has revealed the great diversity of volcanic landscapes beyond the Earth, be they formed by molten rock, liquid water, or other volatile species. Classic examples of giant shield volcanoes, solidified lava flows, extensive ash deposits, and volcanic vents can all be identified but, with the exception of eruptions seen on the Jovian moon Io, none of these planetary volcanoes have been observed in eruption. Consequently, the details of the processes that created these landscapes must be inferred from the available spacecraft data. Despite the increasing improvement in the spatial, temporal, compositional, and topographic characteristics of the data for planetary volcanoes, details of the manner in which they formed are not clear. However, terrestrial eruptions can provide numerous insights into planetary eruptions, whether they result in the emplacement of lava flows, explosive eruptions due to volatiles in the magma, or the interaction between hot lava and water or ice. In recent decades, growing attention has therefore been directed at the use of terrestrial analogs to help interpret volcanic landforms and processes on the terrestrial planets (Mercury, Venus, the Moon, and Mars) and in the outer solar system (the moons of Jupiter and Saturn, the larger asteroids, and potentially Pluto). In addition, terrestrial analogs not only provide insights into the geologic processes associated with volcanism, but they can also serve as test sites for the development of instrumentation to be sent to other worlds, as well as serve as a training ground for manned and unmanned explorers seeking to better understand volcanism throughout the solar system.

Geoturism in Africa. the Simien Mountains

The paper is dedicated to the geological structure of Ethiopia and Simien Mountains, which are located in the northern part of the North Ethiopian Plateau composed of Oligocene plateau basalts hosting Oligocene-Miocene shield volcanoes.

Chapter 5.1a Northern Victoria Land: volcanology

Neogene volcanism is widespread in northern Victoria Land, and is part of the McMurdo Volcanic Group. It is characterized by multiple coalesced shield volcanoes but includes a few relatively small stratovolcanoes. Two volcanic provinces are defined (Hallett and Melbourne), with nine constituent volcanic fields. Multitudes of tiny monogenetic volcanic centres (mainly scoria cones) are also scattered across the region and are called the Northern Local Suite. The volcanism extends in age between middle Miocene (c. 15 Ma) and present but most is <10 Ma. Two centres may still be active (Mount Melbourne and Mount Rittmann). It is alkaline, varying between basalt (basanite) and trachyte/rhyolite. There are also associated, geographically restricted, alkaline gabbro to granite plutons and dykes (Meander Intrusive Group) with mainly Eocene–Oligocene ages (52–18 Ma). The isotopic compositions of the plutons have been used to infer overall cooling of climate during the Eocene–Oligocene. The volcanic sequences are overwhelmingly glaciovolcanic and are dominated by ‘a‘ā lava-fed deltas, the first to be described anywhere. They have been a major source of information on Mio-Pliocene glacial conditions and were used to establish that the thermal regime during glacial periods was polythermal, thus necessitating a change in the prevailing paradigm for ice-sheet evolution.

5. Making and breaking volcanoes

‘Making and breaking volcanoes’ addresses how volcanoes are constructed and denuded and explains the shape of volcanoes and their internal architecture, including the differences between scoria cones, tuff rings, maars, and dome fields, shield volcanoes, and stratocones. Some volcanoes (‘monogenetic’ volcanoes) erupt just once, whereas others (‘polygenetic’ volcanoes) may continue erupting intermittently for millions of years. When sufficient magma is rapidly expelled from the shallow reservoirs beneath the volcano the overlying ground is left unsupported and collapses, creating a large topographic basin known as a caldera. As the caldera founders, its steep sides, formed so abruptly, are unstable and collapse inwards as a series of landslides. Tall volcanoes tend to collapse sideways in giant landslides, then grow and collapse again. Rain and meltwater also wears away volcanoes, forming lahars and floods, and choking drainage systems.