page_title: Volcanism on Io
section_title: Explosion-dominated eruptions (Pillanian Volcanism)
hierarchical_section_title: Volcanism on Io / Eruption styles / Explosion-dominated eruptions (Pillanian Volcanism)
caption_attribution_description: English: NASA's Galileo spacecraft caught this volcanic eruption in action on Jupiter's moon Io on November 25, 1999. This mosaic shows Tvashtar Catena (now called Tvashtar Paterae), a chain of calderas, in enhanced color. It combines low resolution (1.3 kilometers, or .8 miles, per picture element) color images of Io taken on July 3, 1999 with the much higher resolution (180 meters, or 197 yards, per picture element) black and white images taken in November. The molten lava was hot enough, and therefore bright enough, to saturate, or overexpose, Galileo's camera (original image is inset in lower right corner). The bright lava curtain (a chain of lava fountains) and surface flows shown in the color image were assembled as an interpretive drawing by Galileo scientists, based on their knowledge of how the camera behaves when saturated. The lava appears to be producing fountains to heights of up to 1.5 kilometers (5,000 feet) above the surface. Several other lava flows can be seen on the floors of the calderas. The darkest flows are probably the most recent. The elongated caldera in the center of the image is almost surrounded by a mesa that is about 1 kilometer (.6 miles) high. In places the mesas margins are scalloped, which is typical of an erosional process called sapping. This occurs when fluid escapes from the base of a cliff, causing the material above it to collapse. On Earth, sapping is caused by springs of groundwater. Similar features on Mars are one of the key pieces of evidence that water flowed on Mars surface in the past. On Io, the fluid is believed to be sulfur dioxide, which should vaporize almost instantaneously when it reaches the near vacuum at Io's surface, blasting away material at the base of the cliffs. North is to the top of the image and the Sun illuminates the surface from the lower left. The high resolution black and white image was taken at a distance of 17,000 kilometers (11,000 miles). The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC. JPL is a division of the California Institute of Technology, Pasadena, CA. This image and other images and data received from Galileo are posted on the Galileo mission home page at http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm.
context_page_description: Volcanism on Io, a moon of Jupiter, is represented by the presence of volcanoes, volcanic pits and lava flows on the moon's surface. Its volcanic activity was discovered in 1979 by Voyager 1 imaging scientist Linda Morabito. Observations of Io by passing spacecraft and Earth-based astronomers have revealed more than 150 active volcanoes. Up to 400 such volcanoes are predicted to exist based on these observations. Io's volcanism makes the satellite one of only four known currently volcanically active worlds in the Solar System.
  First predicted shortly before the Voyager 1 flyby, the heat source for Io's volcanism comes from tidal heating produced by its forced orbital eccentricity. This differs from Earth's internal heating, which is derived primarily from radioactive isotope decay and primordial heat of accretion. Io's eccentric orbit leads to a slight difference in Jupiter's gravitational pull on the satellite between its closest and farthest points on its orbit, causing a varying tidal bulge. This variation in the shape of Io causes frictional heating in its interior.
context_section_description: Explosion-dominated eruptions are the most pronounced of Io's eruption styles. These eruptions, sometimes called "outburst" eruptions from their Earth-based detections, are characterized by their short duration (lasting only weeks or months), rapid onset, large volumetric flow rates, and high thermal emission. They lead to a short-lived, significant increase in Io's overall brightness in the near-infrared. The most powerful volcanic eruption observed on Io was an "outburst" eruption at Surt, observed by Earth-based astronomers on February 22, 2001.
  Explosion-dominated eruptions occur when a body of magma (called a dike) from deep within Io's partially molten mantle reaches the surface at a fissure. This results in a spectacular display of lava fountains. During the beginning of the outburst eruption, thermal emission is dominated by strong, 1–3 μm infrared radiation. It is produced by a large amount of exposed, fresh lava within the fountains at the eruption source vent. Outburst eruptions at Tvashtar in November 1999 and February 2007 centred on a 25-kilometre (16 mi) long, 1-kilometre (0.62 mi) tall lava "curtain" produced at a small patera nested within the larger Tvashtar Paterae complex.
  The large amount of exposed molten lava at these lava fountains has provided researchers with their best opportunity to measure the actual temperatures of Ionian lavas. Temperatures suggestive of an ultramafic lava composition similar to Pre-Cambrian komatiites (about 1,600 K or 1,300 °C or 2,400 °F) are dominant at such eruptions, though superheating of the magma during ascent to the surface cannot be ruled out as a factor in the high eruption temperatures.
  Although the more explosive, lava-fountaining stage may last only a few days to a week, explosion-dominated eruptions can continue for weeks to months, producing large, voluminous silicate lava flows. A major eruption in 1997 from a fissure north-west of Pillan Patera produced more than 31 cubic kilometres (7.4 cu mi) of fresh lava over a ​2 ¹⁄₂- to ​5 ¹⁄₂-month period, and later flooded the floor of Pillan Patera. Observations by Galileo suggest lava coverage rates at Pillan between 1,000 and 3,000 square metres (11,000 and 32,000 sq ft) per second during the 1997 eruption. The Pillan flow was found to be 10 m (33 ft) thick, compared to the 1 m (3 ft) thick flows observed at the inflated fields at Prometheus and Amirani. Similar, rapidly emplaced lava flows were observed by Galileo at Thor in 2001. Such flow rates are similar to those seen at Iceland's Laki eruption in 1783 and in terrestrial flood basalt eruptions.
  Explosion-dominated eruptions can produce dramatic (but often short-lived) surface changes around the eruption site, such as large pyroclastic and plume deposits produced as gas exsolves from lava fountains. The 1997 Pillan eruption produced a 400 km (250 mi) wide deposit of dark, silicate material and bright sulfur dioxide. The Tvashtar eruptions of 2000 and 2007 generated a 330 km (210 mi) tall plume that deposited a ring of red sulfur and sulfur dioxide 1,200 km (750 mi) wide. Despite the dramatic appearance of these features, without continuous resupply of material, the vent surroundings often revert to their pre-eruption appearance over a period of months (in the case of Grian Patera) or years (as at Pillan Patera).
caption: Galileo images of active lava flows and fountains at Tvashtar Paterae in 1999
exif: {}