North Hawaii News Articles from CFHT
Every resident of the Big Island knows there is an active volcano very
near them. There are other volcanos on Earth too (about 800 are active
or dormant); but did you know that there are volcanos on other planets
A volcano is a vent (crack, hole, any aperture) in a planet's (or a
satellite's) crust from which hot molten rock, steam, water, dust,
ashes, and gasses are ejected. Hot springs and geysers also are
manifestations of volcanic activity, resulting from the interaction of
ground water with magma.
Volcanos have a few causes. On Earth, the most common cause is movement
of tectonic plates; those plates are sections of the terrestrial crust
that float freely on a layer of molten rock. When they collide with one
another or are spread apart, lava flows from the cracks. The other
volcanos on Earth (about 5%) appear above hot spots (like the Hawaiian
volcanos). Elsewhere in our Solar System, giant impacts of comets or
asteroids can break the crust of planets or satellites and release
Space probes have detected the remnants of ancient volcanic eruptions on
the Moon, the red planet Mars, and Mercury. Triton (a satellite of
Neptune), Io (a satellite of Jupiter), and Venus are the only bodies in
the solar system besides Earth that are known to be volcanically active
right now. Recently, Europa, another of Jupiter's satellites, has been
found to show evidence of volcanic activity.
Those eruptions are of rocky material and are driven by internal heat,
except on Io, Triton and Europa. On Io, the eruptions are probably of
sulfur compounds and driven by tidal interactions with Jupiter and its
other major satellites. On Triton, the eruptions are of very volatile
compounds, such as methane or nitrogen, driven by seasonal heating from
the sun. On Europa, what comes out is probably water.
MERCURY and THE MOON
Mercury is the closest planet to our Sun. It looks very similar to the
Moon. Both show a heavily cratered and very old terrain, and
regions of relatively smooth and younger plains. When you watch the
Moon, you can easily see these two types of terrain: the young and
smooth maria (or lunar sea) appear darker.
The Moon's maria are huge impact craters that were later flooded by
On Mercury, some of the plains may be the result of ancient volcanic
activity, but some may be deposits of dirt ejected from craters created
by impacts. A recent reanalysis of Mariner 10 data revealed some
evidence of volcanic activity on Mercury, such as signs of lava flows
and deposits from explosive volcanic eruptions.
Ancient volcanic activity is also seen on Mars. Mars is known to have
the largest volcano in the Solar System, Olympus Mons. (The largest
volcano on Earth is our Mauna Loa, which is 9 kilometers (6 miles) high
from its base, and 120 kilometers (75 miles) across).
This Mars volcano is 550 km (340 miles) across, three times higher than
Earth's highest mountain (about 27 km (17 miles) tall - compare with
Mount Everest which is about 10 km high) and has a volume over fifty
times greater than Earth's largest volcano. The caldera at the top is
over 70 km (45 miles) wide, and surrounding the volcano is a cliff that
ranges up to 10 km in height!
The low gravity on Mars allows such huge structures as large as Olympus
Mons to form. But Olympus Mons is not the only volcano; there is Alba
Patera, with a base diameter of 1,500 kilometers (930 miles); Ceraunius
Tholus, one of the smaller volcanos, but still about the size of the Big
Island; Apollinaris Patera which rises only 5 km (3 miles) or so above
the red surface, and many others.
Besides Earth, Venus, Io and Triton are the only places where we know
volcanic activity is taking place now.
Venus, the second planet from the Sun, has been visited by over 20
unmanned spacecrafts. Most of its surface consists of plains with little
relief, but radar imaging (a technique able to see through the thick
clouds of Venus), has revealed the presence of lava flows on much of the
surface, along with lava channels, cones, domes, and several large
shield volcanos, such as the 8 km high Maat Mons, Gula Mons, and Sif
Mons. Venus also shows interesting and unique features including pancake
volcanos (eruptions of very thick lava) and coronae (collapsed domes
over large magma chambers). Venus is still volcanically active, but only
in a few hot spots.
Io is slightly larger than Earth's Moon and is the closest large
satellite to Jupiter. Its surface is continually changing due to many
powerful volcanos. Hundreds of volcanic calderas have been photographed.
This activity is thought to be caused by Jupiter and its more distant
Galilean Moons (Europa, Ganymede, and Callisto). Constantly pulling on
Io and distorting its shape (by as much as 100 meters), they help
generate internal frictional heating which in turn causes the eruptions.
Photographs sent by Voyager in 1979, and more recently by Galileo, show
ongoing eruptions that eject yellowish lava, probably made of sulfur or
molten silicate rock. Sometimes, the eruptive plumes are 300 km (190
miles) high! Io's most prominent volcano is called Pele, after the
Hawaiian fire goddess.
Europa, another Galilean Moon of Jupiter, presents a smooth icy surface
interrupted by ridges, which may result from volcanic cracks in the ice
where emerging liquid water freezes upon exposure to the cold of deep
space. This is called cryovolcanism, a process related to eruption
of ice and gases in geyser-like activity which shoots gas and rocky debris
from Europa's interior.
Let's skip over the ringed Saturn and pale blue Uranus, to get to
Neptune, the outermost gaseous giant. Triton is its biggest moon, and
almost everything we know about it comes from the only spacecraft
which has passed near Triton, Voyager 2, in 1989. Voyager found a very
thin atmosphere, extensive ridges, valleys criss-crossing the surface
in complex patterns, and, most interesting and totally unexpected,
evidence for ice volcanos. The eruptive material is probably liquid
nitrogen, dust, or methane compounds from beneath the surface. One of
Voyager's images shows an actual plume rising 8 km (5 miles) above the
surface and extending 140 km (86 miles) to one side.
To learn more about our Solar System, there are excellent Web sites that
cover every aspect of each of the planets and satellites of our Solar
Dec. 21, 2000