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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.
Diagram of a Strombolian eruption. (key: 1. Ash plume 2. Lapilli 3. Volcanic ash rain 4. Lava fountain 5. Volcanic bomb 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Dike 10. Magma conduit 11. Magma chamber 12. Sill) Click for larger version.
960 × 312 (4 KB) Jkwchui {{Information |Description ={{en|1=How crater-depth is measured, using the side-view of a typical crater. Depth "A" measures from the surface to the bottom of the crater. Depth "B" measures from the mean height of the rim to the bottom of the crater.}}
The EID lists fewer than ten such craters, and the largest in the last 100,000 years (100 ka) is the 4.5 km (2.8 mi) Rio Cuarto crater in Argentina. [2] However, there is some uncertainty regarding its origins [3] and age, with some sources giving it as < 10 ka [2] [4] while the EID gives a broader < 100 ka. [3]
The depth of an impact crater in a solid planet or moon may be measured from the local surface to the bottom of the crater, or from the rim of the crater to the bottom. Crater depth diagram. The diagram above shows the full (side) view of a typical crater. Depth "A" measures from the surface to the bottom of the crater.
A central-peak crater is the most basic form of complex crater. A central-peak crater can have a tightly spaced, ring-like arrangement of peaks, thus be a peak ring crater, though the peak is often single. [3] Central-peak craters can occur in impact craters via meteorites. An Earthly example is Mistastin crater, in Canada. [1]
The diameter of the original crater is uncertain, but has been estimated to be from 30 to 70 km (19 to 43 mi). [2] Computer simulations of a 7 km (4.3 mi) in diameter impactor crashing into a 2 km (1.2 mi) thick ice sheet covering granite bedrock produced a crater of final diameter compatible with the Yarrabubba crater. [1]
For their 1968 paper [7] that first introduced the concept of a resurgent caldera to geology, [6] R.L. Smith and R.A. Bailey chose the Valles caldera as their model. Although the Valles caldera is not unusually large, it is relatively young (1.25 million years old) and unusually well preserved, [ 31 ] and it remains one of the best studied ...