According to a new paper published today, scientists estimate that flooding from crater lakes on Mars — caused by sudden breaches in the crater rims — could have created as much as 25% of the volume of the valley networks that have been identified there.
Mars’ surface hosted large lakes about 3.5 billion years ago. Some of these lakes overtopped their rims, resulting in massive floods that rapidly formed deep canyons. Similar lake breach floods occurred in the northwest United States and central Asia at the end of the last glacial period over 15,000 years ago.
“We found that at least a quarter of the total eroded volume of Martian valley networks were carved by lake breach floods. This high number is particularly striking considering that valleys formed by lake breach floods make up just 3% of Mars’ total valley length,” Morgan said. “This discrepancy is accounted for by the fact that outlet canyons are significantly deeper than other valleys. These floods would have shaped the overall Martian topography, affecting the flow paths of other valleys. Our results don’t negate the importance of precipitation-fed runoff on early Mars. On the contrary, liquid water had to be stable for long enough for lakes to fill from inlet rivers.” [emphasis mine]
The map above shows in white the Loire Valles on Mars, located at about 20 degrees south latitude in transition zone between the northern lowland plains and southern cratered highlands. The paper cites this valley as a typical example of a flood valley caused by a crater rim breach.
This research only makes the geological and climate history of Mars more puzzling. Though the geological evidence strongly suggests lakes and liquid water once existed on Mars, and this research strengthens that conclusion (as indicated by the highlighted sentence above), no model of the planet’s climate has ever satisfactorily created a situation where that was possible. Either there are factors about Mars’ ancient history we have not yet identified (likely) and don’t yet understand (very likely), or the planet’s geology was formed by processes alien to Earth and thus not yet recognized by us.
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