An impact structure is a generally circular or craterlike
geologic
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...
structure of deformed
bedrock
In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet.
Definition
Bedrock is the solid rock that underlies looser surface mater ...
or
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
produced by
impact
Impact may refer to:
* Impact (mechanics), a high force or shock (mechanics) over a short time period
* Impact, Texas, a town in Taylor County, Texas, US
Science and technology
* Impact crater, a meteor crater caused by an impact event
* Impac ...
on a
planetary surface
A planetary surface is where the solid or liquid material of certain types of astronomical objects contacts the atmosphere or outer space. Planetary surfaces are found on solid objects of planetary mass, including terrestrial planets (including ...
, whatever the stage of
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
of the structure. In contrast, an
impact crater
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 ...
is the surface expression of an impact structure. In many cases, on Earth, the impact crater has been destroyed by erosion, leaving only the deformed rock or sediment of the impact structure behind.
[Neuendorf, K.K.E., J.P. Mehl Jr., and J.A. Jackson, eds. (2005) ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, ]American Geological Institute
The American Geosciences Institute (AGI) is a nonprofit federation of about 50 geoscientific and professional organizations that represents geologists, geophysicists, and other earth scientists. The organization was founded in 1948. The name of ...
. 779 pp. This is the fate of almost all old
impact craters on Earth, unlike the
ancient pristine craters preserved on 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 ...
and other geologically inactive rocky bodies with old surfaces in the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
. Impact structure is synonymous with the less commonly used term astrobleme meaning "star wound".
In an impact structure, the typical visible and
topographic
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary scie ...
expressions of an impact crater are no longer obvious. Any
meteorite
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 Natural satellite, moon. When the ...
fragments that may once have been present would be long since eroded away. Possible impact structures may be initially recognized by their anomalous geological character or
geophysical
Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' som ...
expression. These may still be confirmed as impact structures by the presence of shocked minerals (particularly
shocked quartz
Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal. These pla ...
),
shatter cone
Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions. They are evidence that the rock has been subjected to a shock with pressures in the rang ...
s,
geochemical
Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...
evidence of
extraterrestrial material or other methods.
See also
*
Complex crater
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 call ...
*
Earth Impact Database
The Earth Impact Database is a database of confirmed impact structures or craters on Earth. It was initiated in 1955 by the Dominion Observatory, Ottawa, under the direction of Carlyle S. Beals. Since 2001, it has been maintained as a not-for-prof ...
*
Impact event
An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or me ...
*
List of impact craters on Earth
This list of impact craters on Earth contains a selection of the 190 confirmed craters given in the Earth Impact Database as of 2017.
To keep the lists manageable, only the largest craters within a time period are included. Alphabetical lists f ...
*
List of possible impact structures on Earth
This is a list of possible impact structures on Earth. More than 130 geophysical features on the surface of the Earth have been proposed as candidate sites for impact events by appearing several times in the literature and/or being endorsed by the ...
* ''
Traces of Catastrophe
''Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures'' is a book written by Bevan M. French of the Smithsonian Institution. It is a comprehensive technical reference on the science of impact ...
'' book from
Lunar and Planetary Institute
The Lunar and Planetary Institute (LPI) is a scientific research institute dedicated to study of the Solar System, its formation, evolution, and current state. The Institute is part of the Universities Space Research Association (USRA) and is supp ...
- comprehensive reference on impact crater science
*
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, ...
References
External links
Terrestrial Impact Cratersat the Lunar and Planetary Institute
Earth Impact Database
{{Authority control
Impact geology