Complex craters are a type of large
impact crater morphology.
Above a certain threshold size, which varies with planetary gravity, the collapse and modification of the transient cavity is much more extensive, and the resulting structure is called a ''complex crater''. The collapse of the transient cavity is driven by gravity, and involves both the uplift of the central region and the inward collapse of the rim. The central uplift is not the result of ''elastic rebound'' which is a process in which a material with elastic strength attempts to return to its original geometry; rather the uplift is a process in which a material with little or no strength attempts to return to a state of gravitational equilibrium.
Complex craters have uplifted centers, and they have typically broad flat shallow crater floors, and
terraced walls
A terraced wall, also a terrace wall, or a terraced retaining wall is a wall that is divided into sections ( terraces) over a slope. Such designs are useful when building on a steep grade. Terraced walls may be built with many different material ...
. At the largest sizes, one or more exterior or interior rings may appear, and the structure may be labeled an ''impact basin'' rather than an impact crater. Complex-crater morphology on
rocky planets appears to follow a regular sequence with increasing size: small complex craters with a central topographic peak are called ''
central-peak craters'', for example
Tycho; intermediate-sized craters, in which the central peak is replaced by a ring of peaks, are called ''
peak ring
A peak ring crater is a type of complex crater, which is different from a multi-ringed basin or central-peak crater. A central peak is not seen; instead, a roughly circular ring or plateau, possibly discontinuous, surrounds the crater's center, ...
craters'', for example
Schrödinger; and the largest craters contain multiple concentric topographic rings, and are called ''
multi-ringed basins'', for example
Orientale. On icy as opposed to rocky bodies, other morphological forms appear which may have central pits rather than
central peaks, and at the largest sizes may contain very many concentric rings –
Valhalla
In Norse mythology Valhalla (;) is the anglicised name for non, Valhǫll ("hall of the slain").Orchard (1997:171–172) It is described as a majestic hall located in Asgard and presided over by the god Odin. Half of those who die in combat e ...
on
Callisto is the type example of the latter.
Complex craters are classified into two groups: central-peak and
peak-ring craters
A peak ring crater is a type of complex crater, which is different from a multi-ringed basin or central-peak crater. A central peak is not seen; instead, a roughly circular ring or plateau, possibly discontinuous, surrounds the crater's center, ...
. Peak-ring craters have diameters that are larger in than central-peak craters and have a ring of raised
massifs which are roughly half the rim-to-rim diameter, instead of a central peak.
Central-peak craters
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.
Central-peak craters can occur in
impact craters, via
meteorites
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...
. An Earthly example is
Mistastin crater, in
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
.
Many central-peak craters have rims that are scalloped,
terraced inner walls, and
hummocky floors.
When central peaks form
Diameters of craters where complex features form depends on the strength of gravity of the celestial body they occur on. Stronger gravity, such as on Earth compared to the Moon, causes rim collapse in smaller diameter craters. Complex craters may occur at to on Earth, but start from on the Moon.
If
lunar craters
Lunar craters are impact craters on Earth's Moon. The Moon's surface has many craters, all of which were formed by impacts. The International Astronomical Union currently recognizes 9,137 craters, of which 1,675 have been dated.
History
The wor ...
have diameters between about to , the central peak is usually a single peak, or small
group of peaks. Lunar craters of diameter greater than about may have complex,
ring-shaped uplifts. If impact features exceed of diameter, they are called
impact basins
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
, not craters.
Lunar crater
Lunar craters are impact craters on Earth's Moon. The Moon's surface has many craters, all of which were formed by impacts. The International Astronomical Union currently recognizes 9,137 craters, of which 1,675 have been dated.
History
The w ...
s of to about in diameter possess a central peak.
There are several theories as to why central peak craters form. Such craters are common, on
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
, the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
,
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
, and
Mercury.
Height of central peak relative to crater diameter
On the Moon, heights of central peaks are directly proportional to diameters of craters, which implies that peak height varies with crater-forming energy.
There is a similar relationship for
terrestrial meteorite craters, and
TNT craters whose uplifts originated from rebound.
See also
*
*
*
* ''
Traces of Catastrophe'', 1998 book from
Lunar and Planetary Institute - comprehensive reference on impact crater science
References
{{Impact cratering on Earth
Impact craters
Impact geology