Thread by @geologyonmars

Check out our new paper in @nature. We show that at least 25% of the total martian valley network volume formed from catastrophic lake breach floods (1/10): nature.com/articles/s4158…

Valley networks on #Mars are somewhat analogous to river valleys on Earth but differ morphologically. Maybe this is a sign that instead of forming from precipitation, #martian valleys are a result of groundwater or glacial erosion, or even lava. (2/10)

Alternatively, my co-authors (Goudge et al., 2019) previously showed some valleys formed catastrophically from lake breach flooding. How do we know they were catastrophic? The downstream valley volume closely correlates with the inferred volume of water in the #paleolake (3/10)

So how important were breach floods globally? To find out, we modified an existing map of martian valley networks (Hynek et al., 2010), assigning valley segments as paleolake outlets or valley networks. (4/10)

We then used a Progressive Black Top Hat (PBTH) algorithm developed by Luo et al. (2015, 2017) to estimate the eroded volume within the valley networks. This algorithm identifies valley edges and the depth of valley interiors relative to that edge (5/10)

We find that at least a quarter of Mars’ valleys (by volume) formed from breach floods! This is particularly striking given then they are only 3% of the total valley length. What gives? Breach flood valleys are much deeper! (6/10)

These deep outlet canyons would reset local base level, affecting the morphology of other, non-outlet valleys, such as A, B, and C in this figure. (7/10)

Is this result surprising? It shouldn’t be! The early martian surface was not very hydrologically integrated so when it was warm enough for precipitation water be trapped in lakes, some of which would breach. #wateronmars (8/10)

This is similar to what was going on during the end of Earth’s last glacial period around 15,000 years ago. And that time period also saw lots of breach floods, including the Bonneville flood in southeast Idaho and the Altai flood in central Asia. en.wikipedia.org/wiki/Bonnevill… (9/10)

For more, check out the paper! Thanks to the rest of the team @timgoudge, @Stuck_onEarth, & @marslakes nature.com/articles/s4158… (10/10)