The Amazing Eruptions of Io

Volcanic explosions on Io appear to be relatively frequent occurrences. This Voyager 1 image taken on March 4, 1979, shows a tall plume of lava exploding 100 miles above Io's surface.  The source of the plume is Loki, one of the most volcanically active regions on Io.
Image Credit: NASA/JPL

Summer is almost over, the kids will be back at school soon, but I just couldn't wait and had to find some time to write about the recent discovery of a new volcanic eruption on Jupiter's moon Io. 
       
On Aug 15, 2013 Dr. Imke dePater of the University of California at Berkley, was observing Io with the Keck II telescope on Mauna Kea in Hawaii, when she saw a massive volcanic eruption. This eruption turns out to be one of the top 10 most powerful eruptions observed on Io to date. Dr. dePater and her team have been able to pinpoint the location of this eruption to the Rarog Patera region, which is named for a Czech fire deity.

The Rarog Patera region was first identified in Voyager 1 imagery, where lava deposits appear to flow away from a broad, irregular depression. This region was also identified as a definite hot spot by Dr. Julie Rathbun and her co-workers, using data from the photopolarimeter-radiometer on board the Galileo space craft. However, the noted temperatures in this region are more indicative of an old, cooler lava flow, rather than an active region capable of producing the kind of eruption observed by Dr. dePater. That said, it is possible that Rarog Patera has been active prior to the Galileo mission. In August of 1998, Dr. Rathbun and her colleague Dr. Spencer observed an eruption using NASA's ground-based Infrared Telescope Facility on Mauna Kea in Hawaii. Rarog Patera is one of three possible source candidates for this eruption.   

This mosaic of Io was produced with data from both the Voyager 1 and Galileo missions. The colours are similar to what you would see with the naked eye, but enhanced to accentuate the many volcanic structures that are found on the surface of Io. The black arrow points to the Rarog Patera region, where a powerful volcanic eruption was observed on Aug. 15, 2013. 
Image Credit: NASA/JPL/USGS, with annotation by Irene Antonenko

The black arrow points to the Rarog Patera volcanic region. In this segment of Voyager 1 image PIA01485, lava flows can clearly be seen originating from what looks to be a broad, irregular depression.
Image Credit: NASA/JPL/USGS, with annotation by Irene Antonenko
  

This 200 km U-shaped lava lake in the Loki volcanic region is thought to be responsible for the episodic eruptions that occur here. This Voyager 1 image shows gray spots in the dark lake, which may be due to "icebergs" of solid sulfur in a liquid sulfur lake.
Image Credit: NASA/JPL

If Rarog Patera has erupted in the past, that would make it one of the periodically erupting volcanoes on Io. The most famous such volcano is Loki, which has an eruption cycle of about 540 days, with the actual eruption event lasting on the order of 230 days. This periodicity is thought to result from the cyclical overturning of a lava lake. Quiet times represent periods where the lava lake is covered by a solid crust. When this crust eventually sinks into the liquid lava underneath, it produces a long-lasting eruption event. Most volcanic eruptions on Io, however, are not periodic and are much less short lived than Loki, lasting on the order of days. As more research comes in, it will be interesting to see what kind of eruption Rarog Patera is, and what that tells us about the style of volcanism at this region.

No imagery of the current Rarog Patera eruption has been released yet. But, Io is one of the most volcanically active objects in the Solar System and changes on the surface due to volcanism have been recorded before. In the late 1990's, the Galileo spacecraft acquired multiple images of the Pillan Patera region, showing significant changes over a time span of about 2 years, with new deposits from volcanic eruptions clearly visible. Hopefully, future missions will be able to image the Rarog Patera region, to show us what kinds of changes this very massive eruption has wrought. 

Dramatic changes can be seen in this series of Galileo images of the Pillan Patera region of Io. Taken on April 1997 (left), September 1997 (centre), and July 1999 (right), these images show that a massive dark deposit about 400 km in diameter (upper right) was produced by a volcanic explosion at Pillan Patera sometime between April and September 1997.  Later, an unnamed volcano to the right of Pillan erupted, depositing a smaller patch of dark material, surrounded by a yellow ring.
Image Credit: NASA/JPL/University of Arizona

Sources:
Major Volcanic Eruption Seen on Jupiter’s Moon Io, Universe Today, Aug 23, 2013. 
Huge lava fountains seen gushing from Jupiter moon, New Scientist, Aug 20, 2013.
USGS Geologic map of Io.
Rathbun and Spencer, 2010, Ground-based observations of time variability in multiple active volcanoes on Io, Icarus, V209, pp625-630, DOI 10.1016/j.icarus.2010.05.019.
Rathbun et al., 2004, Mapping of Io's thermal radiation by the Galileo photopolarimeter–radiometer (PPR) instrument, Icarus, V169, pp127-139, DOI 10.1016/j.icarus.2003.12.02.