ISNS 4359
Spring 2005
Steve Bergman, Instructor
Lecture 21. Extraterrestrial Volcanism - Out of this world
"Hot" (~700-1600C) silicate volcanism such as Earth, Moon, Venus, Mars, Mercury, Io (Jupiter moon)
"Cold" (-250-~100C) water and other volcanism on moons Triton (Neptune), Ganymede (Jupiter)
Cryovolcanism-extrusion of water liquids and vapors (entrained solids) of materials that would be frozen
solid at extraterrestrial planetary surface temperatures. {Ice “volcanoes” on earth: US Great Lakes-in winter}
Earth is the only body in our solar system known to exhibit active plate tectonics.
Mercury Heavily cratered surface of highlands and lowland plains. No obvious young lavas, very old (>3.9
billion year) basalt lavas are thought to cover much of the surface; no active plate tectonics, but a magnetic field
suggesting a core dynamo. Hot spots are the probable cause for volcanism.
Venus Dense thick CO2-rich atmosphere; surface covered by basalt lavas; no active plate tectonics; no
magnetic field-no core dynamo. Impact Crater density similar to Earth's Precambrian shields; ~1100 volcanic
landforms identified. <1 to >1000 km diameter shield volcanoes, lava flows, flow fields, lava channels,
calderas, pancake domes, corona; young volcanism <500 million years old (possibly active); hot spots probable;
atmospheric SO2 decreased 90% from 1978-1984, suggesting possible volcanic injection.
Mars Abundant impact craters; Erosion modifies landforms; no active plate tectonics; no magnetic field-no
core dynamo; wide range in age of ancient volcanism: ~100-300 million to 3.9 billion years ago.
Large central shield volcanoes, complex scalloped craters (Paterae), steep sided volcanoes (Tholi), volcanic
plains, lavas, pyroclastic deposits. Hot spots are the probable cause for volcanism. Olympus Mons is the
largest known volcano in the solar system (600 km, 25 km high, summit caldera 65 km).
Earth's Moon Age of volcanism: 3.1-4.5 billion years [volcanism ceased ~1.5 billion years ago.] Lunar
crust ~60 km thick. Possible early mantle convection, now a dead planet. Heat flow ~26 mW/m 2 (Earth 85
mW/m2), consistent with radioactivity, lunar ‘geotherm’ ~400 C colder than peridotite solidusT @ 500 km
depth. No water has been found on the Moon. The Moon has a solid Fe core (300-400 km radius) much smaller
than the earth Impact Crater density is used to date the age of volcanism. (Maria are younger than Highlands).
Moon: 10 craters/million km2/billion years (>10 km diam.; <3.3 Ga); (2.4 craters >20 km diam.)
Maria (“seas”) -Dark-colored, lowland regions of massive basalt lavas cover 17% of surface (first suggested
by Ralph Baldwin in 1949, proved by 4 Apollo & 3 Luna missions in 1969-73 returning 382 kg of rocks).
Lavas up to hundreds of km long, due to lower gravity & 10-1000x lower viscosity than Earth basalts.
Few circular shields /domes (3-17 km); Rare pyroclastics (glass beads) due to spray eruptions.
Terrae (Highlands) -Light-colored, older, rough anorthosite (intrusive rocks modified by impacts) 2 Apollo
missions; global magma ocean 4.0-4.4 Ga.
Outer Planet Moons-mixtures of water ice and rock/metal
Io -only body outside Earth known to have large-scale active volcanism- (most volcanically active of any
Solar System object-100 times as that on Earth). Over 100 volcanoes have been recognized which put out twice
as much heat as all Earth volcanoes. Heat flow 2.5 W/m2 (>50x Earth; ~200x radioactive, due to tidal heating
caused by eccentric orbit near Jupiter & Europa). Volcanic centers - 20-200 km diam. with craters <2 km deep;
~10 active plumes rise 100s of km. Volcano Temperature~1200-1700C (basalt-komatiite?)
Europa-Rocky core, liquid water mantle, icy crust; possible fissure plume detected.
Ganymede- Largest satellite in the solar system; only moon with core dynamo & magnetic field; Icy water lava
flows and calderas.
Neptune Triton Crust of water ice with Frozen Nitrogen polar cap; active geyser-like plumes.
Saturn Enceladus Crust of water ice with flood volcanism, shields and crater chains (cryoclastic).
Titan Cassini-Huygens radar shows possible icy volcanic flows, or it may be an erosive feature.