Ismenius Lacus Region
Topographical Map of the Ismenius Lacus Region
The southern and northern borders of the Ismenius Lacus Region are approximately 3,065 km (1,905 mi) and 1,500 km (930 mi) wide, respectively. The north to south distance is about 2,050 km (1,270 mi). The Region covers an approximate area of 4.9 million square km, or a little over 3% of Mars’ surface area.
Image of the Ismenius Lacus Region
The Ismenius Lacus Region contains the Deuteronilus Mensae and Protonilus Mensae, two places that are of special interest to scientists. They contain evidence of present and past glacial activity. The Region also has a landscape unique to Mars, called Fretted terrain. The northern part of this Ismenius Lacus is covered by the Acidalia Planitia. The largest crater in the Region is Lyot Crater which contains channels probably carved by liquid water.
Lyot Crater with dunes and dust devil tracks
Lyot Crater: The northern plains are generally flat and smooth with few craters. However, a few large craters do stand out. The giant impact crater, Lyot, is easy to see in the central part of Ismenius Lacus. Lyot Crater is the deepest point in Mars's northern hemisphere. The image above of Lyot Crater Dunes shows a variety of interesting forms: dark dunes, light-toned deposits, and Dust Devil Tracks. Dust devils, which resemble miniature tornados create the tracks by removing a thin, but bright deposit of dust to reveal the darker underlying surface. Light-toned deposits are widely believed to contain minerals formed in water. Research, published in June 2010, described evidence for liquid water in Lyot crater in the past.
Dunes on the Move in the Lyot Crater area
Channel and fan in Lyot Crater
South of Lyot Crater is the Deuteronilus Mensae:
Rough Terrain in Dueteronilus Mensae
Eroded terrain in Deuteronilus Mensae, as seen by HiRISE
Deuteronilus Mensae is a region on Mars 937 km across and centered at 43.9°N 337.4°W. It covers 344° -325° West and 40°-48° North. The Deuteronilus region lies just to the north of Arabia Terra and is included in the Ismenius Lacus Region. It is along the dichotomy boundary, that is between the old, heavily cratered southern highlands and the low plains of the northern hemisphere. The region contains flat-topped knobby terrain that may have been formed by glaciers at some time in the past.
Lineated Valley Fill and Lobate Debris Aprons in Deuteronilus Mensae
Many of the valley floors in the Dueteronilus Mensae region exhibit complex alignments of small ridges and pits often called "lineated valley fill." The cause of the small-scale texture is not well understood, but may result from patterns in ice-rich soils or ice loss due to sublimation (ice changing into water vapor). The linear alignment may be caused by downhill movement of ice-rich soil or by glacial flow. For example, flowing ice on Earth typically develops wrinkles or ridges and pits due to stresses in the ice as it moves. The result is flow patterns, called "stream lines" that follow the valleys and curve around obstacles. In this image, stream lines are diverted or curve around the mesas.
South of the Deuteronilus Mensae we come to the Deuteronilus Colles area also along the Dichotomy boundary but closer to the Uplands of Arabia Terra.
The Deuteronilus Colles Area
Features in the Deuteronilus Colles area in Visible Light
The southeastern part of the Ismenius Lacus Region contain part of the Uplands of Arabia Terra. As one enters the region one comes to the Mamers Valles, a giant outflow channel which runs from north to south. Mamers Vallis is a long, winding canyon in the north of Mars. It covers 1000 km, cutting through the cratered uplands of the Arabia Terra, from the Cerulli Crater to the Deuteronilus Mensae near the edge of Mars' vast northern lowlands. Through its midsection, it averages a width of 25 km and a depth of 1200 meters. the most popular theory states that the canyon was likely formed by either water or lava, with the flow from south to north and additional material flowing from the slope toward the valley floor. According to the most popular theory, linear features in the valley bottom indicate possible ice flows and that ice may currently be plentiful. Mamers Vallis is dated to the early Hesperian period, about 3.8 billion years ago.
Wide view of Mamers Vallis with cliffs, as seen by HiRISE.
Fretted terrain in Mamers Vallis
Just to the southeast of Mamers Vallis is Cerulli Crater:
Cerulli Crater Ejecta Valleys, as seen by HiRISE
Cerulli Crater is a crater in the Ismenius Lacus Region on Mars with a diameter of 130 km. It is located at 32.5° north latitude and 337.9° west longitude. It is named after Vicenzo Cerulli, an Italian astronomer (1859–1927).
Back to and east of Deuteronilus Mensae is the Protonilus Mensae. The Protonilus Mensae is an area of Mars in the Ismenius Lacus Region. It is centered on the coordinates of 43.86° N and 49.4° E. Its western and eastern longitudes are 37° E and 59.7° E. North and south latitudes are 47.06° N and 39.87° N. Protonilus Mensae is between Deuteronilus Mensae and Nilosyrtis Mensae; all lie along the Martian dichotomy boundary (ancient shoreline).
Pits and cracks in Protonilus Mensae,
Fretted Terrain: The Ismenius Lacus Region contains several interesting features such as Fretted terrain, parts of which are found in Deuteronilus Mensae and Protonilus Mensae. Fretted terrain contains smooth, flat lowlands along with steep cliffs. The scarps or cliffs are usually 1 to 2 km high. Channels in the area have wide, flat floors and steep walls. Many buttes and mesas are present. In fretted terrain the land seems to transition from narrow straight valleys to isolated mesas. Most of the mesas are surrounded by forms that have been called a variety of names: circum-mesa aprons, debris aprons, rock glaciers.
Glaciers: Glaciers formed much of the observable surface in large areas of Mars. Much of the area in the high latitudes, especially the Ismenius Lacus Region, is believed to contain enormous amounts of water ice. In March 2010, scientists released the results of a radar study of the Deuteronilus Mensae area that found widespread evidence of ice lying beneath a few meters of rock debris. The ice was probably deposited as snowfall during an earlier climate when the poles were tilted more. It would be difficult to take a hike on the fretted terrain where glaciers are common because the surface is folded, pitted, and often covered with linear striations. The striations show the direction of movement. Much of this rough texture is due to sublimation of buried ice. The ice goes directly into a gas (this process is called sublimation) and leaves behind an empty space. Overlying material then collapses into the void.
A Delta in Ismenius Lacus, as seen by Themis. Location is 33.9 N and 17.5 E.
Deltas: Researchers have found a number of examples of deltas that formed in Martian lakes. Deltas are major signs that Mars once had a lot of water because deltas usually require deep water over a long period of time to form. In addition, the water level needs to be stable to keep sediment from washing away. Deltas have been found over a wide geographical range. Above, is a picture of one in the Ismenius Lacus Region.
Coloe Fossae is a set of troughs in the Ismenius Lacus Region of Mars. It is centered at 36.5 degrees north latitude and 302.9 west longitude. It is 590 km long and was named after a classical albedo feature name.
Fretted Valleys in Coloe Fossae area
Fretted Valleys in Coloe Fossae area in Visible Light
Moreux Crater is a crater in the Ismenius Lacus Region on Mars with a diameter of 138 km. It is located at 42.1° north latitude and 315.6° west longitude It was named after Theophile Moreux, a French astronomer and meteorologist (1867–1954).
Moreux Crater moraines and kettle holes, as seen by HIRISE
Unusual surface patterns near the center of Moreux Crater suggest a complicated history of glacial flow. A series of ridges and troughs originating from the crater’s central peak to the west of this image terminate in this area in a jumble of twisted patterns and circular depressions.
Jumbled Flow Patters in Moreux Crater
The superposition of impact craters and sand dunes on top of these ridges and troughs suggests that the flow patterns are old and that any ice may be largely gone. The round depressions may have formed when large sections of relatively clean ice were left in place to melt or sublimate (evaporating ice directly to gas). The ridges would be analogous to moraines in Earth glaciers, formed from rock and debris mixed with the ice that flow with the glacier. The complicated and twisting patterns indicate that the ice flowed into this area, which is at a lower elevation on the crater floor, and piled up behind itself as the flow stalled. Numerous boulders are also scattered over the surface of ridges and troughs. Boulders may have been carried into place with the ice and as the ice was removed, the boulders were left in place. This the last major crater north of the Uplands of the Sabaea Terra along the Dichotomy boundary until we come to the next major Region to the East.
Banded Bedrock of Terra Sabaea
Possible theories: Such colorful bedrock is typical of ancient Mars, when water played a more active role in altering minerals. Tectonics is the movement of rocks under the great forces within a planet’s interior. Mars probably had very active plate tectonics early in it’s history and may still be active today on a much smaller scale. What we see today seems to be driven mainly by gravity. The primary focus in tectonics is to understand the forces that are bending and breaking the rocks. The first step in gaining this understanding is to measure exactly how and when the rock were deformed. One idea is that the global scale tectonics on Mars can be related to the weight of Olympus Mons and the other volcanoes in the Tharsis area. This idea makes very specific predictions for how the deformation will be oriented (cracks will generally be "radial" (point to) Tharsis and ridges will be "concentric" to (encircle) Tharsis). Another basic question is whether the many fissures that are seen on the surface of Mars are formed by magma pushing up form underneath or if they formed first, producing an area of weakness that rising magma could exploit. Finally, the way the rocks bend or break tells us a lot about what they are made of. Most sedimentary rocks that have been laid down in water will bend easier than hard lava.