Volcanoes

This post is for the monthly geoblogosphere carnival called the Accretionary Wedge. This month’s Accretionary Wedge is being hosted by Chris Town at Good Schist.

Source: Jet Propulsion Laboratory

Prior to Voyager 1’s flyby of Io in March of 1979, geologists and other scientists back home on Earth had evidence that active volcanism was currently only taking place on our own planet. There was plenty of evidence that volcanism happened on other celestial bodies in the past, such as Olympus Mons on Mars and the large basalt flows on our own Moon.

Voyager 1’s flyby changed that by giving us direct evidence that extraterrestial volcanism was actively happening on other celestial bodies. An engineer at the Jet Propulsion Laboratory in Pasadena, California was analyzing images from the recent flyby of Io and noticed a plume emanating from the surface.

Discovering plumes on Io, taken in March of 1979 by Voyager 1.
Source: NASA, www.nasaimages.org

Since scientists initially discovered those plumes nearly 30 years ago, Io has been the focus of much research and observation. We now know that it is one of the most volcanically active bodies in our solar system, having to deal with the gravitational tug of war subjected on it by Jupiter. The Hawaiian Volcano Observatory has an excellent explanation on why Io is so volcanically active:

Io is situated between Jupiter and two of Jupiter’s large moons - Europa and Ganymede. The gravitational force exerted by Jupiter and its moons creates a tidal bulge more than 100 meters (330 feet) high on Io’s surface. Remember, this is a tide created in the solid rock of Io’s crust! As Io rotates around Jupiter, the tidal bulge moves, Io’s crust is flexed, and tremendous heat is generated - much like the heat generated in a piece of wire when it is quickly bent back and forth. This heat drives the volcanic activity so prevalent on Io.

100 meter tides that move through the solid crust of Io? That is ridiculous!

Active volcanism on Tvashtar, a volcano on Io. Captured by the New Horizons spacecraft in March of 2007.
Source: Jet Propulsion Laboratory

What is all the lava that erupts on Io composed of? Scientists do not know for certain the composition of the lava, but based on spectrometer data, Io’s surface is covered with a mix of hot, basaltic or ultramafic silicates and a sulfur dioxide frost.

Distribution of Sulfur Dioxide Frost on Io
Source: NASA, www.nasaimages.org

Potential Source of Sulfur Flow on Io
Source: NASA, www.nasaimages.org

The low gravity and atmospheric pressure on Io create a perfect recipe for large and spectacular eruptions. Eruption plumes on Io can range from a height of 38 miles to more than 250 miles above the surface of the moon! This is why the plumes are so easy to pick out in photos from the various space probes that have passed the moon.

New Horizons captured this unique view of Jupiter’s moon Io March 1, 2007.
Source: NASA, www.nasaimages.org

Voyager 1 acquired this image of Io on March 4, 1979.
Source: NASA, www.nasaimages.org

Voyager 1 image of Io showing active plume of Loki on limb.
Source: NASA, www.nasaimages.org

The temperature of lava flows and lakes on Io can be as high as 3,000 degrees Fahrenheit. The fall out and deposits from these nearly continuous eruptions rapidly change the surface of Io and the resulting deposits create beautiful mosaics of color.

Pillan Patera - Arizona-sized Io Eruption
Source: NASA and JPL

More Information

• The Gish Bar Times - Galileo observations of volcanic plumes on Io
• Keck Observatory - Eruption on Io Rivals Largest in Solar System
• USGS - An Eye on Io’s Volcanism
• USGS - Extraterrestrial Volcanism
• Wikipedia - Io
• Wikipedia - Tidal Heating
• Wikipedia - Volcanism on Io

28 years ago today, Washington state’s Mount St. Helens catastrophically erupted, becoming the largest volcanic eruption in the lower 48 states.

Image credit: USGS

A type of lava formed from very fluid basaltic flows is called pahoehoe. In today’s geology picture of the day, we see a beautiful example of ropey pahoehoe from Hawaii Volcanoes National Park.

Image Credit: bgustus2000 on flickr.

For more information on the types of lava, visit Instant Hawaii.

One of the more interesting types of pahoehoe lava is called ropey pahoehoe and looks like a series of twisted ropes spaced evenly along the ground. The twisted ropes may be fairly straight, or may loop and wind in and out much like a fingerprint. Many visitors express interest in what could create such an unusual shape, but once you see ropey pohoehoe lava being created it is instantly clear how the shapes occur. As the pahoehoe flows, it usually encounters some minor barrier that slows up the front of the flow. As the front of the flow is slowing down, the faster flow behind it pushes the front and forces it to create a small ridge, which it pushes up and over the barrier. That ridge begins to cool and creates the next barrier, which in turn creates the next. The result is a series of ridges interspaced with valleys - which looks like 4 inch thick ropes of lava laying side by side or looping side by side. To walk over ropey pahoehoe it is best to walk on the top of the ridges, perpendicular to the ridges.

Today’s geology picture of the day is from the ongoing Chaiten eruption (which started unexpectedly at the beginning of this month in Chile). Ralph Harrington at The Volcanism Blog has been providing wonderful updates on the eruption.

This photo was captured on May 6 and shows electrostatic discharges as a result of the ash cloud above the volcano.

Image Credit: Carlos Gutierrez