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Lesson FourThe Isum and Lei-Kung Region
ReviewIn the last lesson, we learned about the Amaterasu-Surt Region of Io. This region has been active lately, as shown by the Hubble Space Telescope in May 1998 using its NICMOS instrument. However, images taken by Galileo in July and August 1999 show that most of the active volcanoes have not changes a bit. There are some signs of changes at Surt and Tiermes but that can't be confirmed. Also, changes at Surt could be due to lighting effects rather than real changes. Today's Quadrangle
In today's lesson, we will discuss the Isum region of Io. This area is jam packed with lava flows, sapping cliffs, and pyroclastic flows. This area covers the area on Io from 21.5 to 65.5 deg. North latitude and 180 to 270 deg. West Longitude. This puts it in the Antijovian, trailing, and northern hemispheres of Io. Many volcanoes exist in this area from Isum Patera to Donar Fluctus to the largest active lava flow in the Solar System, Lei-Kung Fluctus. In addition to these volcanoes, there are several volcanoes, including Nile Montes. Lei-Kung FluctusLei-Kung Fluctus is the undisputed champion of lava flows in the solar system. Lei-Kung Fluctus is centered at 45 deg. North Latitude and 215 deg. Longitude and is over 450 km long. Only Masubi Fluctus in Tarsus Regio might beat it in size but not volume. In several areas in this lava flow, Lei-Kung can reach over 90 km wide. Lei-Kung is believed to have erupted from a source at 64 deg. North Latitude and 195 deg. West Longitude. This lava flow is active, though it has not increased in size in 20 years. The current lava front is to the south at 35 deg. North Latitude and 205 deg. West Longitude. This area was detected as active in November 1996 and November 1997. In fact, the lava erupting in Nov. 1997 was measured at 1440 Kevin, consistent with very hot silicate lavas on Earth. It is possible that the lava erupting at that time maybe ultramafic in nature. In addition to the flow front detected as hot, the PPR instrument on Galileo detected a large warm spot centered at 50 deg. North Latitude and 225 deg. Longitude. PPR measured it as 108 Kelvin, warmer than the Io nighttime average of 90 Kelvin. With the exception of flow front, Lei-Kung is mantled with yellow sulfur. In addition, bright white deposits surround the lava flow, more than likely caused by past plume activity. This again indicates that most of Lei-Kung has not erupted in 20 years. Despite that, Lei-Kung churns on at the flow front, adding layer after layer of lava to the Ionian surface. Isum PateraSouth of Lei-Kung Fluctus is a giant plateau that I call the Isum Plateau. Near the center of this plateau is a dark volcano called Isum Patera. Isum Patera is located at 29 deg. North Latitude and 208 deg. Longitude and is 100 km wide. Isum Patera is a persistent hotspot, meaning that over 75% of the time, Isum is shown by either ground-based imaging, Galileo, HST, or Voyager to be active. At one point, in November 1997, Isum was erupting with lava that was at least 1350 Kelvin, within the range of silicate lava. Surrounding Isum Patera is a radial pattern of dark pyroclastic flows, probably caused by lava fountains at the caldera. To the west of Isum, is a mushroom-shaped region of bright red pyroclastic flows, probably sulfur. Northwest of Isum Patera is a 250 km long fissure running as far north as possibly Fo Patera. This fissure is surrounded by pyroclastic flows indicating lava curtain activity at the fissure. It is believed that this kinds of activity occurred in November 1997 when a hotspot was seen at the fissure. The temperature was measured at 1450 Kelvin but this could be of lava flowing away from the fountain so this should be considered a lower limit. The fissure does show similarities to the linea on Europa but it is not known whether they are similar in formation. To the southwest of the plateau is a volcano called Itzamna Patera (22 N, 220 W). This 150 km wide volcano was seen as a hot spot in March 1998 by the NIMS instrument on the Galileo spacecraft. An island can be seen in the middle of the Itzamna caldera.
Images taken in February 2000 show the highest resolution views ever taken of the Ionian surface. They images were taken of a "dark" area at 32 deg. North Latitude and 193 deg. Longitude. This dark area is very near the cliff seen there. This cliff is believed to be sapping. On Io, sapping occurs when SO2 liquid/gas escapes from the bottom of a cliff. Shortly afterward this gas freezes a forms a characteristic white deposits. Sapping also leaves a cavity at the bottom of a cliff. This makes the top of the cliff unstable, thus the top collapses and leaves a debris field surrounding the cliff and leaving the cliff having irregular edges. In this cliff, large chunks can be seen at the bottom of it. In the images above, sheets of SO2 ice that are evaporating can be seen. The ice that is left is very layered and the underlying dark soil can be seen in some places. In addition, bright SO2 frost can be seen covering some of the dark soil areas. In the right image, a sharp cliff is surrounded by dark, bumpy material. Heiseb Patera and Girru PateraThese two volcanoes, Heiseb and Girru Patera are located west of the Isum Plateau. Both are located in a large sulfur lava plain. It is not yet known where the sulfur lava originated. Heiseb Patera is located at 29.7 deg. North Latitude and 244.8 deg. West Longitude. It has never been detected as active. The same is not true for Girru Patera. Girru, located at 22.0 deg. North and 240 deg. West Longitude, was active, as seen by Galileo, in September 1996, November 1997, and March 1998. In November 1997, it was measured at 1620 Kelvin, making it well within the range of erupting ultramafic lava. However, despite having such hot lava, no dark lava flows have ever been seen at Girru, unlike other hotspots of that temperature like Amirani and Pillan. Shakuru PateraShakuru Patera is a very oblong caldera located at 23.6 deg. North Latitude and 266.4 deg. West Longitude. The reason for its oblong shape has to do with its location near a mountain to the caldera's west. Shakuru has been detected as active only by Voyager so this volcano is probably not active today. However, despite not being detected as active, it still has a very dark floor. Donar Fluctus
Donar Fluctus is a sub circular caldera surrounded by a series of lava flows. It is located at 21.8 deg. North Latitude and 187.3 deg. West Longitude. The flows are relatively wide, 20 km, trending NW and SW from the caldera. To the east of the Donar caldera, several comparatively narrow lava flows radiate to the northeast, east, and southeast. These flows are less than 2 km wide. The flows range from 5-70 km long and can be linear and sinuous. The lava flows likely formed when lava overflowed the caldera. To the southwest of the volcano, a linear canyon can be seen running roughly N-S. Nile MontesA set of two mountains can be seen at 52 deg. North Latitude and 253 deg. Longitude. Of the two mountains, the NW one appears newer. The Northwest mountain appears to have a slanted southwest slope and a collapsed northeast face. This is consistent with other block mountains which will be discussed later. The southeastern mountain shows signs of collapsing outward though a central peak remains. That mountain can be likened to a pile of sand. Another mountain can be seen at 57 deg. North Latitude and 201 deg. Longitude. This mountain shows signs of sapping. Bright white deposits surround many of the cliffs, especially the south facing cliff of the northeast mountain. Fo Patera and the Colchis KnobFo Patera is located at 40.5 deg. North Latitude and 192 deg. Longitude. Galileo showed that Fo was active in June and November 1996 and February 1997. South of Fo Patera is what is known as the Colchis Knob. This extremely bright extension of Colchis Regio which runs along the bottom of the quadrangle is a SO2 snowfield. A bright ring outlines this deposit, possibly due to fine-grained SO2 frost of unknown origin. In the next lesson, we will discuss the Amirani-Tvashtar region of Io.
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