Tutorial
Water
Mars has an intriguing number of water-related features for a planet that is so dry and cold in the present day. There is plenty of evidence that points to widespread water activity in Mars' past. Features that look similar to river channels on Earth are easily observed, along with island-like forms and river delta features. Mars is known to have large deposits of water ice today, with the largest amounts visible on the surface at the north and south poles. There is no concrete evidence that liquid water currently exists on Mars, though some scientists think that it could occur in certain regions for short amounts of time.
It is exciting that Mars appears to have once had an abundance of water! The presence of liquid water is necessary for life as we know it to survive. If Mars harboured liquid water for long enough periods of time, it is possible that life evolved on the Red Planet. Whether life ever arose on Mars is one of the biggest and most challenging questions for planetary scientists today.
Braided Channels
A braided channel is actually a series of small channels that wind together and apart, forming a pattern that resembles a braid. They are very curvy and occur when there is a lot of sediment being carried by the water. On Earth, braided channels are often found in close association with glaciers.
Practice identifying braided channels
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Braided channels near Hale Crater
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Warrego Valles, a collection of dendritic channels (daytime IR view)
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Two channels: Nirgal Vallis and Ladon Vallis (daytime IR view)
Yes, these are braided channels!
The channels in this image branch out and reconnect around many streamlined islands and other features, like a braid—hence the name "braided channel".
These are dendritic channels.
Can you see the tree shape of these channels? The many branches (“tributaries”) come together into a single channel as the water flowed downhill in Mars’ distant past, flowing from north to south (top to bottom of the image). Braided channels on the other hand branch out and reconnect around islands and other obstacles like strands of hair in a braid.
These are not braided channels.
The channels in this image do not resemble braids, as they don’t flow around islands or obstacles and then reconnect. Nirgal Vallis, the channel running sideways across the left side of the image, has a jagged shape that suggests it may have formed from the surface collapsing over areas of subsurface water. Channels like these are found in northern Arizona and southern Utah on Earth.
Outflow Channels
Outflow channels are very large and wide channels that occur when massive amounts of water trapped behind some kind of natural dam or underground bursts out and floods across the surface of a planet. These channels are carved very quickly relative to river channels.
Practice identifying a outflow channels
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Volcanic vent and flows in Cerberus
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Topographic view of Kasei Valles, a massive outflow channel
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A Martian channel in daytime IR
This is a volcanic vent.
The dark material originating at the cracks in the ground near the centre of the image flows toward the south (bottom of the image). This material is a lava flow that has hardened to form rock, showing that this is not an outflow channel carved by water.
Yes, this is an outflow channel!
The key to identifying outflow channels on Mars is the scale. Look at the scale bar at the lower left of this image—this channel is huge! Martian outflow channels are very large and formed very quickly from the release of massive quantities of water, possibly released from underground aquifers (reservoirs of water). These channels contain streamlined islands and in some places may have a braided-looking appearance.
This is not an outflow channel.
This channel is much smaller than Martian outflow channels and lacks features like streamlined islands.
Streamlined Islands
Streamlined islands are teardrop-shaped islands that form when water runs around a topographic high (on Mars, often the ridge of an impact crater). The pointy end of the teardrop points in the direction of water flow.
Practice identifying a streamlined islands
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Volcanic vent and flows in Cerberus
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Topographic view of Kasei Valles, a massive outflow channel
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A Martian channel in daytime IR
These are sand dunes.
These dark features do have a streamlined appearance, but they are formed by wind rather than water. Sand dunes of this shape are called barchan dunes. Their shape indicates the main direction of wind blowing in that region—in this case, from northeast to southwest (upper right to lower left of the image).
This is a wind streak.
While streamlined islands form behind impact craters like the feature in this image, this is not a streamlined island. The streaks to the left of this crater form from wind blowing around the crater rim, removing fine-grained dust from the surface in the dark areas and depositing dust in the lighter area.
Yes, these are streamlined islands!
The teardrop-shaped features in this image are the streamlined islands. They lie within a large outflow channel on Mars called Tiu Valles, carved by sudden releases of massive volumes of water, possibly from underground aquifers (reservoirs of water).
Dendritic Channels
Dendritic channels are water-related features that look like a branching tree. They form when rivers flow downhill over solid rock.
Practice identifying dendritic channels
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Volcanic vent and flows in Cerberus
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Topographic view of Kasei Valles, a massive outflow channel
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A Martian channel in daytime IR
Yes, these are dendritic channels!
Can you see the tree shape of these channels? The many branches (“tributaries”) come together into a single channel as the water flowed downhill in Mars’ distant past, flowing from north to south (top to bottom of the image). Dendritic channels tend to form in very solid (non-porous) rock.
This is a volcanic vent.
The cracks in this image are volcanic vents. The channels emanating from them were carved by either the release of water or lava, but they lack the tree-like shape of dendritic channels.
These are gullies.
The channels in this image are carved into the wall of a large impact basin called Hale Crater. They are called gullies, which on Earth are often found on the slopes of mountains and are carved by landslides initiated by rain and/or melting snow. On Mars, these channels may be carved by the release of underground water, or melting ice or snow.
Deltas/Fans
Deltas form where a river runs into a larger body of water, such as an ocean or lake. A single channel "fans" out into smaller, more curvy channels as sediment carried by the river is deposited at its mouth (where the river meets the ocean/lake).
Practice identifying deltas/fans
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Volcanic vent and flows in Cerberus
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Topographic view of Kasei Valles, a massive outflow channel
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A Martian channel in daytime IR
This is a landslide.
The "apron" of material near the centre of this image formed from a landslide off the valley wall above it. Landslides occur when slopes of hills or mountains become unstable. Seismic activity (like earthquakes) and sudden saturation (wetting) are two common triggers for landslides.
These are gullies.
These channels ("gullies") carved into the wall of an impact crater in Mars’ southern hemisphere have aprons of material at their bases. The aprons formed by the transport of material from the crater wall downslope through the channels.
Yes, this is a delta!.
This is the Eberswalde Delta, the first striking evidence discovered for liquid water having flowed on the surface of Mars for extended periods of time. The delta lies at the mouth of a channel where it enters Eberswalde Crater. The channels carved in the delta itself were buried after their formation, with sediment filling the channels and covering the surrounding terrain inside the crater. Over time these sediments eroded away within the crater but were preserved within the channels, leaving the channels themselves "inverted" relative to the surrounding terrain—instead of being carved into the ground like channels you tend to see on Earth, these channels would tower above you if you were standing next to them on Mars.