Small Pale Red Planet Issue 1 Phase 8

The Diacria Region

MC-02

 

Image of The Diacria Region

The southern and northern borders of the Diacria 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.

 

Topographical Map of the Diacria Region

The Phoenix Lander’s landing site (68.22° N, 234.25° E) lies about 186 km north of the northeastern quarter of the Diacria Region. The landscape viewed by the Phoenix lander is probably representative of a large portion of the terrain in the northern Diacria Region.
The highest elevation about 3.5 km (3,500 m) above datum (Mars "sea level") on the western flank of the Alba Mons volcano in the southeastern portion of the Region.

The Alba Mons volcano in SW corner of Region

Western flank of Alba Mons:  The western flank of the Alba Mons volcano makes up the eastern and southeastern edge of the Region. In terms of area, Alba Mons (formerly, Alba Patera) is the largest volcanic feature on Mars. The flank has a very low slope (l° or less) and is characterized by lava flows and an outwardly radiating array of ridges and channels. Some of the channels have a drainage pattern that resembles that formed by rainwater on the slopes of terrestrial volcanoes. However, many other channels on the flanks of Alba Mons were clearly formed by flowing lava. The western flank of the volcano also contains some NW-SE trending grabens (Cyane Fossae).

Terrain of the Cyane Fossae area on the west flank of Alba Mons

An image from High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) beautifully shows a line of rimless pit craters in Cyane Fossae. The pits may have formed by the collapse of surface materials into open fractures created as magma intruded the subsurface rock to form dikes.

Pit craters in Cyane Fossae.

The northern and western areas of the Region lie in the northern lowland plains of Mars and cover portions of Amazonis Planitia (in the south), Arcadia Planitia (west central) and Vastitas Borealis (in the north).

Milankovic Crater: is a crater in the Diacria Region  of Mars, having a diameter of 118.4 km. It is located at 54.7° north latitude and 146.7° west longitude. The crater is easy to see on Mars photographs because it lies north of Olympus Mons and sits by itself in the flat plain of Vastitas Borealis. It is named after Milutin Milanković, a Serbian geophysicist and astrophysicist, who lived from 1879 to 1958.

Milankovic Crater

The Arcadia Planitia is a smooth plain with fresh lava flows and Amazonian volcanic flows on Mars. Giovanni Schiaparelli named it in 1882 after the Arcadia region of ancient Greece. It dates from the Amazonian period's Arcadia formation's lava flows and small cinder cones. It includes a more recently developed large region of Aeolian materials derived from periglacial processes. It is located northwest of the Tharsis Region in the northern lowlands, spanning the region 40-60° North and 150-180° West in  the Cebrenia Region and centered at  46.7°N 192.0°E. Arcadia marks a transition from the thinly cratered terrain to its north and the very old cratered terrain to the south. On its east, it runs into the Alba Mons volcanoes. Its elevation relative to the geodetic datum varies between 0 and -3 km.   In many of the low areas of Arcadia, one finds grooves and sub-parallel ridges. These indicate movement of near surface materials and are similar to features on earth where near surface materials flow together very slowly as helped by the freezing and thawing of water located between ground layers. This supports the proposition of ground ice in the near surface of Mars in this area. This area represents an area of interest for scientists to investigate further. Arcadia Planitia and Southern Vastitas Borealis:  The geologic history and origin of the northern plains are complex and still poorly understood. Many of the landforms resemble periglacial features seen on Earth, such as moraines, ice-wedged polygons, and pingos. Arcadia Planitia and Vastitas Borealis likely consist of a hodgepodge of old lava flows, ice-related features, and reworked sediments of diverse origin. Some theorize that oceans or large lakes once covered the northern plains.

Details of the  Arcadia Planitia Region

The Amazonis Planitia: is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces, to the west of Olympus Mons, in the Amazonis and Memnonia Regions, centered at 24.8°N 196.0°E. The plain's topography exhibits extremely smooth features at several different lengths of scale.  Part of it is located in the southwest part of the Daicria Region.

Amazonis Planitia area

 

Acheron Fossae is a trough in the Diacria Region of Mars. Its location is centered at 37.67° north latitude and 135.87° west longitude. It is 718 km long and is named after a classical albedo feature at 35°N, 140°W . The trough has seen intensive tectonic activity in the past.

The Acheron Fossae Trough

Lycus Sulci (Olympus Mons Aureole):  Lycus Sulci (24.6° N, 219° E) is the name applied to the northwestern portion of a larger terrain feature that partially encircles Olympus Mons and extends up to 750 km from the giant shield volcano’s base.  An aureole is a  zone of altered  rock around a volcano.

A view Near the Lycus Sulci area

This feature, called the Olympus Mons aureole, consists of several large lobes and has a distinctive corrugated or grooved surface texture. East of Olympus Mons, the aureole is partially covered by lava flows, but where it is exposed it goes by different names (Gigas Sulci, for example).The origin of the aureole remains debated, but it was likely formed by huge landslides or gravity-driven thrust sheets that sloughed off the edges of the Olympus Mons shield

The lava flows of the Lycus Sulci coming from Mons Olympus

The Erebus Montes: Grooves indicate movement. Westward from Lycus Sulci, across the flat plains of Amazonis Planitia, lies an elongated region of knobby terrain called Erebus Montes (Erebus Mountains). The region contains hundreds of clustered to isolated hillocks that stand 500 to 1,000 m above the surrounding plains. The presence of numerous partly filled "ghost" craters in the area indicates that the hills represent the high-standing remnants of ancient highland crust that was inundated by lava flows and (possibly) alluvial sediments from Tharsis in the southeast and the Elysium volcanic province to the west.

The Erebus Montes