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A volcanic crater is a bowl-shaped depression in the ground caused by volcanic activity, usually located above the volcano's vent. [11] During volcanic eruptions, molten magma and volcanic gases rise from an underground magma chamber, through a conduit, until they reach the crater's vent, from where the gases escape into the atmosphere and the magma is erupted as lava.
The plains predate the heavily cratered terrain, and have obliterated many of the early craters and basins of Mercury; [4] [7] they probably formed by widespread volcanism early in Mercurian history. Mercurian craters have the morphological elements of lunar craters—the smaller craters are bowl-shaped, and with increasing size they develop ...
The formation of new craters is studied in the lunar impact monitoring program at NASA. [4] The biggest recorded crater was caused by an impact recorded on March 17, 2013. [5] [6] Visible to the naked eye, the impact is believed to be from an approximately 40 kg (88 lb) meteoroid striking the surface at a speed of 90,000 km/h (56,000 mph; 16 mi/s
The Pre-Nectarian period is defined from the point at which the lunar crust formed, to the time of the Nectaris impact event. Nectaris is a multi-ring impact basin that formed on the near side of the Moon, and its ejecta blanket serves as a useful stratigraphic marker. 30 impact basins from this period are recognized, the oldest of which is the South Pole–Aitken basin.
It is not clear whether they are of volcanic or impact origin. [4] The inter-crater plains are distributed roughly uniformly over the entire surface of the planet. Caloris Basin —Mercury's largest impact crater (left side of image), is surrounded by a ring of mountains with chaotic terrain following this and eventually leading to smooth and ...
Shield volcano in Tharsis region on Mars with marked borders, circles represent impact craters counted by crater counting method. Crater counting is a method for estimating the age of a planet's surface based upon the assumptions that when a piece of planetary surface is new, then it has no impact craters; impact craters accumulate after that at a rate that is assumed known.
The series are based on referents or locations on the planet where surface units indicate a distinctive geological episode, recognizable in time by cratering age and stratigraphic position. For example, the referent for the Upper Noachian is an area of smooth intercrater plains east of the Argyre basin.
A blanket of ejecta is formed during the formation of meteor impact cratering and is composed usually of the materials of that are ejected from the cratering process. Ejecta materials are deposited on the preexisting layer of target materials and therefore it form an inverted stratigraphy than the underlying bedrock.