Many parts of Texas are experiencing severe drought (though not quite as severe as the b*tch that was the 2011 drought). As a result of these exceptionally dry conditions, a certain riverbed in Dinosaur Valley State Park has run dry, exposing previously undiscovered dinosaur tracks that are roughly 113 million years old. How is this possible—like, how have they not been eroded by the river? Water is pretty excellent at eroding rock, especially over the course of 113 million years. On the one hand, I do understand that most likely the river has not been there as long as the dinosaur tracks have been, but on the other hand (1) we actually don’t know this for sure, and (2) even if it has been there for less time than the tracks have been, there certainly has still been ample time to erode them away. What am I missing here?
[https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjWsazb4t_5AhXRk2oFHVUIBawQvOMEKAB6BAgGEAE&url=https%3A%2F%2Fwww.cnn.com%2F2022%2F08%2F23%2Fus%2Fdinosaur-tracks-discovered-texas-park%2Findex.html&usg=AOvVaw2co9awHFuiD-qAeMOP5DNk](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjWsazb4t_5AhXRk2oFHVUIBawQvOMEKAB6BAgGEAE&url=https%3A%2F%2Fwww.cnn.com%2F2022%2F08%2F23%2Fus%2Fdinosaur-tracks-discovered-texas-park%2Findex.html&usg=AOvVaw2co9awHFuiD-qAeMOP5DNk)
*EDIT/UPDATE: Aha! It now makes sense. It turns out that these particular dinosaur tracks were first discovered in 1908, when a layer of rock that had been covering the tracks broke up and washed away due to a flood. In the time since then, there have been multiple paleontological excavations that have revealed even more of the tracks. And the most important thing to know here—the thing that ties it all together and makes everything “click”—the River* ***has*** *been eroding the prints ever since the first tracks got exposed in 1908. It’s just that obviously on a geological timescale, the 114 years between 1908 and now are just a tiny, minuscule blip in the grand scheme of things… nowhere near long enough for the tracks to have been eroded. So it all makes sense, knowing that the river has only been eroding the tracks for 114 years instead of 113 million years.*
*Source:* [*https://www.nps.gov/…/nature/making-dino-prints.htm…*](https://www.nps.gov/dena/learn/nature/making-dino-prints.htm?fbclid=IwAR3MZ-SQHiJg8uZ7LEjeSZTNgE705yDE4x54VFmrHZgGdySHhI5kLdXgcO4#:~:text=When%20dinosaurs%20walked%20through%20the,where%20people%20can%20see%20them)
In: 1541
water is a powerful erosional force but what really gives it the power are things like suspended material (sediment, tiny pieces of other rocks/minerals (think silica sand), debris, etc) within the water, the overall discharge (how MUCH water is moving through the space, is it narrow and a lot of water or wide and shallow) and the gradient of the overall watershed (meandering stream over 200 miles in Nebraska vs rapid loss of elevation from high point to low point over 20 miles). If you have crystal clear water w/ no suspended load (either in the water column or kinda dragging/bouncing along the bottom of the channel) then your erosional power is muted. A moving water source with lots of suspended load (like the Colorado River, pre dams) then your erosional power is greater (Grand Canyon). Like I stated before, combine suspended load with gradient, discharge & the general temporal history in the space (did a fault move and the stream was redirected and therefore hasn’t been flowing over that space “all that long”) impact the overall erosional effectiveness of moving water.
So that is a very simple approach, in application a lot of other factors could play a part, like others have said, a clay-rich rock without much interstitial cement (between the grains) is gonna be easy to erode while a sandstone with abundant silica cement holding the grains together is going to be much tougher… I mean even down to the grain shape (surface area) will effect how quickly it erodes.
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