Geology / Astrogeology Definitions
Geology / Astrogeology Definitions
The following are some geology definitions that are useful for understanding features on Earth, as well as other planets, and moons. Many of these definitions are used in describing features on the Moon and Mars.
The definitions on this page have mostly been taken from Wikipedia,
in many cases with little alteration.
Some have been rephrased or re-explained
to make understanding easier, and using less terms.
Below each definition the primary source of the information is listed
is the "See:" section, allowing for
the primary source of the terms to be seen or to get more information.
A
Aluvial Fan
is a accumulation of sediments that fans out from a concentrated
source of sediments.
Aluvial fans typically form where flow emerges from a confined channel and then is free to spread out over a wider area and infiltrate the surface.
This reduces the carrying capacity of the flow and results in sediments being deposited.
Aluvial fans typically form where flow emerges from a confined channel and then is free to spread out over a wider area and infiltrate the surface.
This reduces the carrying capacity of the flow and results in sediments being deposited.
Aluvium
Loose sediments (clay, sand, silt, gravel) deposited by running water on plains,
flood plains, alluvial fans, or related landforms.
B
Bedrock
is the solid rock that lies under looser looser surface material (such as sand and soil)
The various kinds of weathered and broken looser material that may lie above the bedrock is called regolith.
The various kinds of weathered and broken looser material that may lie above the bedrock is called regolith.
Braided channel
(or braided river or braided stream)
is a network of river channels separated by small islands called braid bars
Braided channels usually occur in rivers with high sediment loads, or coarse grain sizes, and in rivers with steeper vertical gradients than typical rivers with straight or meandering patterns.
Braided channels usually occur in rivers with high sediment loads, or coarse grain sizes, and in rivers with steeper vertical gradients than typical rivers with straight or meandering patterns.
C
Channel Head
is the (higher elevation) part of a network of channels (that form a river or rivers) where water begins to flow between identifiable banks
D
E
Escarpment
is a steep slope or long cliff that forms as a result of faulting or erosion
and seperates two relatively level areas having different elevations.
A scarp is often used interchangeably with escarpment.
A scarp is often used interchangeably with escarpment.
F
Fault
A fracture or discontinuity in a volume of rock, where there
has been a significant displacement as a result of rock-mass movements.
Fault line / Fault trace is where the fault can be seen or mapped on the surface.
There are 3 types of faults:
Fault line / Fault trace is where the fault can be seen or mapped on the surface.
There are 3 types of faults:
- strike-slip is where the (movement of the two surfaces) offset is predominantly horizontal parallel to the fault line (fault trace).
- dip-slip is where the offset is predominantly vertical and/or perpendicular to the fault line (fault trace).
- oblique-slip is is a combination of strike-slip and dip-slip faults.
Fossa
(fossae)
A long narrow shallow depression on the surface of another planet or Moon.
(derived from Latin, meaning ditch or trench).
E.g. Fossa on Mars
E.g. Fossa on Mars
Floodplain
(or flood plain)
is an area of land adjacent to a river,
stretching from the banks of a river channel to the base
of the enclosing valley, and experience
flooding during periods of high discharge.
Due to regular flooding, floodplains often are often highly fertile, since nutrients are deposited with the flood waters. This encourages farming.
Many agricultural regions, and urban areas have developed near on or flood plains to take advantage of the nutrient-rich soil and water source.
The Nile river basin is an example of a flood plain.
Due to regular flooding, floodplains often are often highly fertile, since nutrients are deposited with the flood waters. This encourages farming.
Many agricultural regions, and urban areas have developed near on or flood plains to take advantage of the nutrient-rich soil and water source.
The Nile river basin is an example of a flood plain.
G
Glacier
A persistant body of dense ice that is constantly moving under its own weight
H
I
J
K
L
M
N
O
Outcrop
An outcrop is where there is a visible exposure of bedrock (or ancient superficial deposits)
Bedrock can become exposed (forming an outcrop) in situations where the underlying cover (such as sand or vegetation) is removed through (often rapid) erosion or tectonic processes.
Outcrops are often seen on steep hillsides, mountain ridges, and river banks, and tectonically active areas.
Bedrock can become exposed (forming an outcrop) in situations where the underlying cover (such as sand or vegetation) is removed through (often rapid) erosion or tectonic processes.
Outcrops are often seen on steep hillsides, mountain ridges, and river banks, and tectonically active areas.
P
Q
R
Ridge
is a long narrow elevated landform, structure or feature seperated
from the surrounding terrain by steep sides.
The sides of a ridge slope downwards from a narrow top which is called the crest or ridgecrest. If the crest is narrow it is also called a ridgeline.
Ridges can be created from deposited material, from erosion or tectonic forces, or a combination of these.
The sides of a ridge slope downwards from a narrow top which is called the crest or ridgecrest. If the crest is narrow it is also called a ridgeline.
Ridges can be created from deposited material, from erosion or tectonic forces, or a combination of these.
River island
Any exposed landmass surrounded by river water
S
T
Terra
(terrae)
An extensive land mass
E.g. Arabia Terra (Mars)
E.g. Arabia Terra (Mars)
U
V
W
X
Y
Z