Phoenicis Lacus (Gradfeld)

The Phoenicis Lacus quadrangle covers the area from 90 to 135 degrees west longitude and 0 to 30 degrees south latitude on Mars. The volcanoes Pavonis Mons and Arsia Mons are believed to have once had glaciers on them. Glaciers may still exist under a layer of thin rocks. The ice can be a source of water for the possible future colonization of the planet.

Lava channels

Lava sometimes forms a tube as it moves away from the vent (opening from which lava flows from a volcano). The top of a stream of lava will cool down, thereby forming a solid roof. The lava will continue moving in the tube. Often, when the lava all flows away, the roof will collapse, making a channel. These features are found on Mars. Some can be seen around Pavonis Mons, in the picture below. Some people have suggested that future colonists on Mars could use the lava tunnels as shelters. They would offer great protection from radiation, especially ultraviolet radiation. Lava Channels on the flank of the volcano Pavonis Mons are pictured below in a picture from Mars Odyssey THEMIS. Sometimes the lava tube remains intact for a time. Lava will break out along the tube to accumulate or flow away. Lava flows often have a lobate appearance at the edges. A good view of such a lava tube is shown below.

Glaciers

Many of the volcanoes on Mars show strong evidence of past and possible present glacial activity. When glaciers melt and retreat, they leave behind material that was carried in and on the ice. Often the material is dropped in a ridge, called a moraine. An example of moraines is showed in the picture below from the flank of Arsia Picture taken with the Mars Odyssey THEMIS.

Dark Slope Streaks

A picture below shows dark streaks on the slopes of Aganippe Fossa. Such streaks are common on Mars. They occur on steep slopes of craters, troughs, and valleys. The streaks are dark at first. They get lighter with age. Sometimes they start in a tiny spot then spread out and go for hundreds of meaters. They have been seen to travel about obstacles, like boulders.It is believed that they are avalanches of dust that expose a darker underlying layer. However, several ideas have been advanced to explain them. Some involve water or even the growth of organisms. Fine dust is common in most places on Mars.

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  Map of Phoenicis Lacus quadrangle with major features labeled. This area contains two large volcanoes, Pavonis Mons and Arsia Mons, as well as the famous Noctis Labyrinthus canyon system.
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  Lava tubes were once covered over with lava flowing in them, but the roofs have now collapsed and the lava has left. Also, some straight troughs (grabens) crosscut the lava channels.
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  Tube fed lava flow. Note accumulations of lava at various places along the tube.
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  Arsia Mons showing its position among other volcanoes as seen by THEMIS.
• Aganippe Fossa as seen by HiRISE. Click on image to see layers and streaks.
  Aganippe Fossa as seen by HiRISE. Click on image to see layers and streaks.