Mount Morning is a shield volcano at the foot of the Transantarctic Mountains in Victoria Land, Antarctica. It lies 100 kilometres (62 mi) from Ross Island. Mount Morning rises to an elevation of 2,723 metres (8,934 ft) and is almost entirely mantled with snow and ice. A 4.1-by-4.9-kilometre-wide (2.5 by 3.0 mi) summit caldera lies at the top of the volcano, and several ice-free ridges such as Hurricane Ridge and Riviera Ridge emanate from the summit. A number of parasitic vents mainly in the form of cinder cones dot the mountain. The volcano was initially active during the Miocene and erupted in two separate stages with a hiatus in between. The older stage has a different chemical composition than the recent one and is heavily eroded by glaciers. The most recent parasitic vents were active about 20,000 years ago, and the volcano could erupt again.
Geography and geomorphology Mount Morning lies in Victoria Land, about 100 kilometres (62 mi) from Ross Island and at the foot of the Transantarctic Mountains. The Koettlitz Glacier runs along the northwestern foot of Mount Morning and separates it from the Royal Society Range 25 kilometres (16 mi) away. Mount Discovery lies next to Mount Morning and is separated from it by the Discovery Glacier. The volcano was originally described in the early to middle 20th century, before more detailed analyses took place in the 1970s, 1980s, and 2000s. The climate in the area is polar, although parts of the ice melt in the sunshine during summer. The volcano rises to 2,723 metres (8,934 ft) above sea level and is capped by a 4.1-by-4.9-kilometre-wide (2.5 by 3.0 mi) caldera that may be the source of a glacier at its northeastern end. Mount Morning has been defined as a 30-by-36-kilometre (19 mi × 22 mi) large shield volcano that consists of a central volcano overlying an older volcanic complex. With a volume of 1,785 cubic kilometres (428 cu mi), it is one of the largest volcanoes in the region. Fissure vents have produced at least 185 parasitic vents on the slopes of Mount Morning. They are cinder cones, fissure ridges, lava domes, and volcanic necks, and their diameters range from a few metres to a few hundred metres. Many of the vents form alignments, some cone craters overlap or the vents themselves have linear shapes. These linear patterns define northeast–southwest trends, with a minor northwest–southeast alignment. Lava flows emanate from cones and make up the present-day surface of the volcano. Mount Morning is almost entirely covered with snow and ice except where it is ablated by southerly winds. Outcrops of volcanic rocks form the north-northeastern Riviera Ridge and northeastern Hurricane Ridge on the northern flank, Mason Spur on the southern flank, and on Helms Bluff on the eastern flank. Gandalf Ridge is a promontory formed by northward-tilted debris and penetrated by dikes. It is located at the foot of Hurricane Ridge, and Pinnacle Valley is located on the Riviera Ridge. Dikes, lava domes, lava flows, and pyroclastic deposits are found in outcrops. Mason Spur also contains breccias from pillow lavas, while Gandalf Ridge features a diamictite and a cross-cutting fault. Mason Spur was considered by Martin et al. 2021 to be a separate volcano from Mount Morning. Owing to the lack of running water, the main edifice (unlike Mason Spur, where traces of marine and water erosion are present) is uneroded and parasitic vents have a young appearance. Glacial erosion has eroded some parts of the volcano, leaving volcanic necks in Pinnacle Valley, has etched glacial striations into exposed volcanic rocks and deposited glacial till. The Vereyken Glacier descends the northeastern slopes of Mount Morning between Hurricane Ridge and Riviera Ridge. Moraines occur on these two ridges and moraines dating to the Wisconsin glaciation have been reported. Glaciers descending from Mount Morning feed the Koettlitz Glacier. Several lakes are found on the volcano and at its foot, including Lake Morning at the end of the Riviera Ridge and Lake Discovery at the foot of the Hurricane and Gandalf ridges.
Geology The West Antarctic Rift is a major geological feature in Antarctica and one of Earth's largest continental rifts. It is a region of active crustal extension and spreading, which may be ongoing today. Volcanic activity occurs at the rift and includes the McMurdo Volcanic Group, a 2,000-kilometre-long (1,200 mi) chain of volcanoes in Victoria Land. This volcanic group has erupted alkaline lavas during the course of the Cenozoic. It is subdivided into three provinces: the Hallett, the Melbourne, and the Erebus province; Mount Morning is the southernmost volcano of the Erebus province. Mount Morning rises from a Paleozoic basement, the Koettlitz Group which crops out close to Gandalf Ridge in the form of granite and metasedimentary rocks. Based on rocks erupted by Mount Morning, the crust appears to be thin and has a calc-alkaline composition. Tectonic sutures in this basement may have allowed magma to ascend to the surface in the Mount Morning region.
Composition Basanite is the dominant rock of outcrops, with phonolite less common and picrobasalt and tephrite rare. Outcrops of older rocks include mugearite, rhyolite and trachyte. Textures range from porphyritic to seriate. Various phenocrysts are found within the volcanic rocks, including aegirine, augite, clinopyroxene, alkali feldspar, kaersutite, nepheline, olivine, plagioclase, quartz, and sanidine. Aegirine, aenigmatite, amphibole, augite, clinopyroxene, alkali feldspar, glass, iron oxide-titanium oxide, nepheline, plagioclase, and quartz make up the groundmass. The volcanic rocks contain xenoliths consisting of syenite and of rocks from older stages of Mount Morning activity. Spinel, peridotite, and less commonly clinopyroxenite, dunite, harzburgite, lherzolite, norite, pyroxenite, and websterite have been reported as xenoliths. The early volcanic rocks of Mount Morning are comparable to mildly alkaline rocks from Mount Melbourne, while the more alkaline late volcanic rocks resemble these from Mount Erebus. The older rocks define the "Mason Spurr lineage" while the younger ones are referred to as the "Riviera Ridge lineage". Basaltic rocks are concentrated on the lower slopes, while phonolite is mainly found in the upper sector of Mount Morning. The composition changes between the early and late volcanic activity of Mount Morning may be due to alteration in crustal magma processes.
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