A variety of shield volcanoes can be found in selected locations on the lunar surface, such as on Mons Rumker. These are believed to be formed by relatively viscous, possibly silica-rich lava, erupting from localized vents. The resulting lunar domes are wide, rounded, circular features with a gentle slope rising in elevation a few hundred meters to the midpoint. They are typically 8–12 km in diameter, but can be up to 20 km across. Some of the domes contain a small pit at their peak. A lunar dome is a type of shield volcano that is found on the surface of the Earth's Moon. They are typically formed by highly viscous, possibly silica-rich lava, erupting from localized vents followed by relatively slow cooling. Lunar domes are wide, rounded, circular features with a gentle slope rising in elevation a few hundred meters to the midpoint. They are typically 8–12 km in diameter, but can be up to 20 km across. Some of the domes contain a small craterlet at the peak. Some of the domes have been shown to consist of the same materials as the lunar maria. Thus they could be created by some mechanism that differs from the mare-forming flows. It is thought that these domes are formed from a smaller magma chamber that is closer to the surface than is the case for a mare. This results in a lower pressure, and so the lava flows more slowly. The magma wells up through a crack in the surface, but the flow eventually concentrates through one primary vent. This concentration can then result in a vent crater at the peak of the dome. There are concentrations of l
nar domes near the craters Hortensius, Marius and T. Mayer, and across the top of Mons Rumker. Solitary lunar domes are also found on the near side, including Kies Pi (?), Milichius Pi (?), Mons Gruithuisen Gamma (?) and Delta (?), and a dome near the craters Gambart C, Beer and Capuanus. Omega Cauchy (?) and Tau Cauchy (?) form a pair of domes near the crater Cauchy. Likewise near Arago are the domes Arago Alpha (?) and Arago Beta (?).Mons Rumker is an isolated volcanic formation that is located in the northwest part of the Moon's near side, at selenographic coordinates 40.8° N, 58.1° W. The feature forms a large, elevated mound in the northern part of the Oceanus Procellarum. The mound has a diameter of 70 kilometres, and climbs to a maximum elevation of about 1,100 metres above the surrounding plain. It was named after Karl L. C. Rumker. Mons Rumker has a concentration of 30 lunar domes—rounded bulges across the top, some of which contain a small craterlet at the peak. These are wide, circular features with a gentle slope rising in elevation a few hundred meters to the midpoint. Lunar domes are the result of lava erupting from localized vents followed by relatively slow cooling. Mons Rumker is surrounded by a scarp that separates it from the adjacent mare. The plateau rises to an altitude of 900 m in the west, 1,100 m in the south and 650 m in the east. The surface of Mons Rumker is relatively uniform, with a strong spectroscopic signature of lunar mare material. The estimated volume of lava extruded to create this feature is 1,800 km3.