Tuesday, May 25, 2010

1st Day of the CR_Evolution Workshop

The first day of the Colorado River Workshop has now ended and things are as I suspected they might be for me - exhaustive! I got home at 7:30 last night and couldn't decide if I was wide awake ready for more, or just merely ready for bed. It didn't matter - I woke up at some unruly hour in the middle of the night and couldn't get the river or the canyon out of my head. I missed my morning walk but am using the extra time to write a few words about some of my impressions. I'll be back at the 2nd day of the proceedings at 8 AM today and am listed as a co-author on two of the talks.

Overall, everyone was pretty good natured about presenting their ideas, although the two sets of black boxing gloves visible on one of the entry tables wasn't entirely a joke. At least no one screamed but there was a few hearty discussions concerning the lower river (downstream from Hoover Dam). The format of the Workshop is like this: An agenda has been made and you can read it here. Each speaker gets five minutes to present their findings or ideas and then five minutes of discussion after that. That's not a typo. It's five minutes. And fortunately it's policed pretty stringently. It's enough time to show three or four slides although others push that to ten (and then end up being surprised that the five minutes went by so quickly). A cell phone type ringer goes off when each five minutes are up. It's a pretty good system and keeps things moving without having to endure long-winded talks.

There was at least one earth-shattering idea presented in the morning. Brian Wernicke of Cal Tech proposes that a river carved the entire Grand Canyon to within a few hundred meters of its present depth between 80 and 70 million years ago! Not only that, but this river was going in the the opposite direction towards Colorado and Wyoming. For those of you who have read "Carving Grand Canyon" this may not seem like such a new idea, since Don Elston and Andre Potochnik have also proposed such a vision. But Wurnicke uses a technique called thermochronology, which essentially measures when the now removed, overlying rocks were stripped off the ones we can see in the canyon today. (The two previous ideas spoke to surface evidence only). Wernicke has been a giant in the study of the Basin and Range for the last 20 years and this is his first entry into the Grand Canyon debate.

He calls his river the California River (get it - the modern Colorado River flows into California but the ancient California River flowed into Colorado). You can read his abstract here (although it's unfortunate he did not include a map shown in his talk that depicts the California River going from the Sierra's through the Grand Canyon exactly in the alignment familiar to us today and on into northern Colorado. (Remember the Sierra's were much closer to Grand Canyon before Nevada was stretched into the Basin and Range only after 20 Ma. The Sierra's in this depiction were in the approximate position of Las Vegas). I hope to obtain a copy of this map when I see him today.

On the other end of the time spectrum, Kyle House and colleagues provide outstanding evidence from the lower Colorado River between Hoover Dam and Blythe for the catastrophic filling of basins that overflowed sequentially downstream. These basins were separated by bedrock sills and essentially mirror the dammed basins today (Lake Mojave, Lake Havasu, etc.) All of this occurred in the 5 Ma time frame. You can read their abstract here. This seems to argue for a very young river, at least for its lower reach. Amazing the two frames between Wernicke and House.

Wish I had time to write more this morning but I gotta go hear more. Stay tuned.

4 comments:

Toni said...

Wow! Keep writing.

Gaelyn said...

I have to say that Wernicke's idea makes more sense to me than the current idea of a 5-6 Ma carving of the already uplifted Colorado Plateau. What do you think Wayne? Interested to hear more.

Gaelyn said...

I have to say Wernicke's idea makes more sense to me than the current explanation of a 5-6 Ma Colorado River carving through an already uplifted Colorado Plateau. What do you think Wayne? Interested in hearing more.

Apologize if this comes thru twice.

Wayne Ranney said...

Gaelyn,
Thanks! Brian Wernicke is presenting his information with conviction based on his data for when the rocks appear to become exhumed. He is not the first geologist to propose such an idea (Don Elston was the first) but this evidence, although "outnumbered" by younger ideas, needs to be reckoned with. WR