Lesson Three

The Amaterasu-Surt Region

Review

Last time, we learned about the north pole region of Io.  Not much exists there that we know of.  A lot of what we know is based on what we learn from space probes that visit the Jupiter system and a lot of what we don't know is due to the limitations of those same space probes.  These limitations could be the imagers spectral range, the spatial resolution of the camera, or the trajectory of the space probe.   Trajectory is the biggest limitation for understanding the north polar region of Io.  No spacecraft has yet to fly over of the north pole thus observations must be done at great distances and emission angles.  There is hope.  Currently, the Galileo spacecraft is planned to fly over the North pole in August of 2001.

Today's area

In today's lesson we discuss the region north of Loki Patera (discussed briefly in lesson one and more fully in lesson seven).   This area covers longitudes 270 deg. West to 360 deg. West and latitudes 21.5 deg. North to 65.5 deg. North.  This puts this area in the northern, projovian, and trailing hemispheres.  This area encompasses many major volcanic center such as Surt and Amaterasu as well as a few minor ones.  We will discuss all these features.

Surt

This volcano is located at 45.5 deg. North Latitude and 337.9 deg. Longitude.  In the image above, Surt is the brown caldera to the upper left of the bright spot just left of center.  Bright SO2 deposits dominate the landscape south and especially east of the Surt caldera.  Surt is an active hotspot, occasionally sending up a Pele-type plume.  Deposits from this plume were seen in images taken by the Voyager 2 spacecraft in July 1979.  The deposits apparently formed between March and July 1979 because they were not there during the Voyager 1 flyby.  Also, the bright deposits shrunk and darkened, covered up by the plume deposits.  Alas, by the time that Galileo arrived in 1996, the bright deposits had returned and the plume deposits had faded away indicating that Surt had not been active since Voyager 2 flew by or at least in the last few years.

Incidentally, Surt has been seen as a hotspot during the Galileo era.   In July 1998, the NICMOS instrument on the Hubble Space Telescope discovered a hotspot around the area where Surt is.  Could the sleeping giant that erupted with a vengeance in 1979 be waking up?  Images taken by the Galileo spacecraft in May 1998 show that the caldera has darkened and the bright deposits have shrunk.  No Pele-type plume deposits can be seen but it does look like that Surt is waking up.

Amaterasu Patera

Amaterasu is an extremely dark caldera at 38 deg. north Latitude and 307 deg. Longitude.  In the quadrangle image, it is the caldera just to the lower right of center.  The brightness of this caldera shows wild fluctuations from very dark (.04 albedo during the Voyager era and Galileo orbits E6 and E15) to moderately dark (.15 albedo during Galileo orbit G1).  At the time of the darkening of Amaterasu, a hotspot was seen there by NIMS which lasted for 3 months or more.  In addition, Amaterasu was detected as a hotspot by Voyager when the caldera was extremely dark.   This means that volcanic eruptions on Amaterasu cover old material that has been lightened by pyroclastic debris or plume deposits.  Could subtle albedo changes at other calderas like at Chaac be excellent indicators of active hot spots?  This appears to be the case Amaterasu.

In addition to a lava covered caldera, Amaterasu is associated with a south-bound sheet of lava. The lava is gray and black.  This lava appears to be covered in a red deposit, which fluctuates in brightness along with volcanic eruptions at the main volcano.  Could this be a plume deposit from Amaterasu?

Other Volcanoes

In addition to Amaterasu and Surt, there are five other known hotspots in this quadrangle.  They are: Manua Patera, Fuchi Patera, Tiermes Patera, Kinich Ahau Patera, and Dazhbog Patera.  In addition to the hotspots, two other areas of interest are Atar Patera and a bright area at 60 N, 330 W.   Also numerous unnamed calderas can be seen at: (35 N, 336 W), (35 N, 343 W), (48 N, 302 W), (47 N, 308 W), (50 N, 279 W), (26 N, 280 W), (27.5 N, 317 W), and (46 N, 356 W).

Manua Patera

Manua Patera is located at 35.5 deg. North Latitude and 322  deg. Longitude.  Manua is 110 km across making it a fairly large caldera.  In the quadrangle map above, Manua is the caldera just west of Amaterasu Patera.  Manua has been sighted as a hot spot only twice, in February 1997 during an eclipse observation by SSI during orbit E6 and by the adapted optics camera at the Canada-France-Hawaii telescope on July 16, 1997.  Both times the hotspot was very faint but these are the only times that the volcano has been firmly detected.  Images taken in E15, after the eruptions of 1997, show that the dark spot along the edge of the Manua caldera have not changes size.   It is possible that the eruptions only produced a small amount of lava or they have been covered up with lighter plume material.

Dazhbog Patera

Dazhbog Patera is located at 56 deg. North Latitude and 303 deg. Longitude.  Dazhbog can be seen just north of center in the quadrangle image above.   This volcano is very stealthy. In Voyager images, this caldera is quite prominent with its dark reddish floor with a darkish halo around the caldera.  However, in Galileo images it is hard to tell where the volcano it.  The area where it is supposed to be is dark making the caldera undistinguishable from its surroundings.   One would suspect that that would mean that it was inactive but in July 1998, the Hubble Space Telescope using its NICMOS instrument detected a hotspot at Dazhbog.   Sadly, images that would have shown the changes if any are unavailable at the time this lesson was written.  Perhaps in a future update the aftermath of this eruption can be learned and told.

Kinich Ahau Patera

This newly named caldera is located at 50 deg. North Latitude and 312 deg. Longitude or just southwest of Dazhbog Patera.  This volcanoes was detected as being active in July 1998 by the NICMOS instrument onboard the Hubble Space Telescope.  In Voyager images, this volcano is large with a small, inner caldera that has a dark floor.   This dark, inner caldera, is located at 49 deg. North and 312 deg. West.  It is this inner caldera that is believed to be the source of the mid-1998 eruption.  In images taken in May 1998 by the Galileo spacecraft, the entire caldera complex of Kinich Ahau was shown to be much darker than during the Voyager flybys.  Also red deposits could be seen north west of Kinich Ahau.  It can not be determined whether they belong to Dazhbog or to Kinich Ahau. If the red deposit is from a Marduk-type plume, then it more than likely came from Dazhbog because almost all Marduk-type plumes in the northern hemisphere stream southwest and west.  However, the fact that the red deposits appear to be emanating from Kinich Ahau may destroy that belief.

Fuchi Patera

This known hotspot is located at 29 deg. North Latitude and 328 deg. Longitude.  This puts it just southwest of Manua Patera.  Fuchi is a 45 km wide caldera with a semi-dark floor. Voyager images show a possible two-tiered structure to the floor of the caldera with the north being lower than the southern and margin area of the caldera being higher up.  A hotspot was detected at this location on June 2, 1996 and in July 1998.  The July 1998 hotspot was detected by the NICMOS instrument on the Hubble Space Telescope.  No changes were seen here by Galileo between 1979 and 1996 and during the actual Galileo mission.  It is possible that a hot spot was detected by the SSI instrument in May 1997.

Tiermes Patera

Tiermes Patera is located at 23 deg. North Latitude and 351 deg. Longitude.  This puts it near the left edge of the quadrangle map above.   Tiermes erupted violently in July of 1995 and continued to erupt until that September.  Tiermes has never been detected as a hot spot since.  Tiermes has a dark surface indicating recently active lava flows.  Tiermes was to have been imaged at very high resolution by the NIMS instrument onboard Galileo in November 1999 but an a fault in the spacecraft forced it to miss the first half of its observations during the Io flyby, which included the Tiermes observation.

Atar Patera

Atar Patera is located at 30.2 deg. North Latitude and 278.9 deg. Longitude  This 125 km wide caldera has never been detected as a hotspot and is covered in orange deposits.  A few lava flows can also be seen emanating from Atar.   It is possible that these are sulfur flows or ancient silicate flows.  In addition, concentric rings can be seen like steppes within the volcano itself.

"The Bright Spot"

A large bright area can be seen at 60 deg. North Latitude and 330 deg. Longitude. A dark streak runs northwest to southeast through the middle of this bright region.  This may indicate that a volcano exists at the center of this area and that the bright spot is a product of this volcano.  No hotspots have ever been detected there.

In the next lesson we will discuss the volcanoes of the "Isum Plateau."