Avulsion dynamics and experimental sedimentation
Back in February during Just Science Week, I posted a bit about some of the work being done regarding experimental sedimentation (see here).
I highlighted the work being done by sedimentologists and dynamicists at the University of Minnesota’s St. Anthony Falls Lab in particular.
The video below is from some of their work…I encourage you to explore their data archive if you want to find more. This video shows a time lapse of sedimentation occuring on an experimental delta. This particular experiment nicely shows the dynamics of shifting pathways of sediment transport and/or deposition/erosion, otherwise known as avulsion. The deposit here would be more akin to a braided fan delta as it is not developing long-lived channels with cohesive levees.
The annotation shows where and when avulsion and expansion of channelized flow occurs. Also keep your eye on where deposition is occuring. This interplay of deposition and avulsion continues in a very dynamic (and seemingly unpredictable) fashion. Qualitatively, this isn’t really anything we haven’t known for a long time. The point with these experiments is that we can measure every last little detail. These researchers are really just scratching the surface — eventually they would like to try develop some fundamental quantitative relationships that might lead to predictive guidelines. But, it will take many years of experimentation to amass the data needed to converge on these relationships.
The photo below is shown on SAFL’s web page currently…it shows that they are now experimenting with systems that do produce cohesive levees, which is a key ingredient for understanding the dynamics of most river deltas.
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Friday Field Foto #17: Clast imbrication
Today’s field photograph comes from the Valley of Fire region in Nevada. A few years ago we organized a student-led field trip to this area to check out some of the fantastic geology on display.
This particular photo shows nice clast imbrication in a Cretaceous alluvial fan sequence. Note the three clasts just below the pencil stacked on each other showing the paleocurrent direction to the right. If you go hike around on a modern alluvial fan or stream with cobbles in it, you will likely find small piles of imbricated clasts just like this.
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1980 Mount St. Helens eruption anniversary
Today marks the 27th anniversary of the famous Mount St. Helens eruption. At 8:32 am on May 18th, 1980 the volcano erupted as half the mountain slid off the side.
This GoogleVideo would not properly embed on the blog (and I can’t be bothered to figure it out), but if you click on the image below it will take you to the page where you can view that famous clip of the eruption.
The geoblogosphere has had some discussions in recent months regarding the accuracy and quality of Wikipedia when it comes to geologic information. In this case, I think the Wikipedia entry on Mount St. Helens does a decent job at laying out the important information. And, as Wikipedia entries go, it has a very nice list of notes and external sites at the bottom of the page to get more information.
Below is a map of the ash fallout from the 1980 eruption. I wonder why there is that isolated patch in Oklahoma?
Humpback whales in Sacramento
Two humpback whales, a mother and her calf, have found themselves about 90 miles from the Pacific Ocean. They swam through the Golden Gate and then upstream through the Sacramento-San Joaquin Delta, where they are now apparently hanging out.
image from: http://www.physorg.com/news67103763.htmlThe mother was injured by a boat propeller and has a 2-foot long 6-inch wide gash near her dorsal fin. Marine biologists are hoping to lure the wayward animals toward the Pacific with recordings of whale songs where they can find food and the salty water can heal the mother’s injury.
Where on (Google)Earth #11?
I’ve been slackin’ on putting together a good post on this blog lately….in the meantime, enjoy this latest installment of Where on (Google)Earth?
This one might be difficult…i’m zoomed in a little more than usual.
Good luck!
Catalina Island wildfire
If you’re following the news even a little bit, you’ve probably heard about the wildfire burning up Catalina Island, which is offshore of southern California. Click image above or quote below to read story and see more photos. Although many people live on the island, much of it is a wildlife refuge.
Here is a bathymetric map showing the island. See more here.
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Friday Field Foto #16: Sand injectites
Okay, back to Patagonia for this week’s photo.
Tres Pasos Formation at El Chingue Bluff, southern Chile (© 2007 clasticdetritus.com)
This isn’t in my specific field area, but very close to it and in the same formation. What’s really cool about this area is the presence of clastic dikes….or, what have now been termed “injectites”, as in the injection of sand. In this photo you’ll notice the light-colored streaks cutting up and to the right across the flat-lying strata. These features are sandstone.
Injectites have been recognized for over a hundred years, but have been more appreciated in recent years. Oil companies searching for petroleum in the North Sea have seen huge networks and complexes of injectites with seismic-reflection data. And I mean huge…some of the individual sandstone “dikes” can be kilometers long cutting sub-vertically through the strata.
In the case above, the orientation of this swarm of injectites are parallel to a growth fault (i.e., syn-depositional) lower in the section.
There is still much debate about the mechanics of these things…what kinds of overpressures are required, how fast is the unlithified sand injected, and so on.
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Video of flash flood
Here is a great video of a flash flood in Thompson Canyon, which is in Utah and very near these outcrops. This particular video was shot by Doug Jerolmack last summer. I found this on Paul Heller’s website, which is a great resource for videos of clastic sedimentation.
Note the debris-rich front of the flow, full of twigs, sticks, and other stuff (pause at 00:19). After some time, the debris-poor part of the flow comes through.
Pause at 00:34 and note the levee of woody debris that has formed on the edge of the flow. This is a defining characteristic of these types of flows and help keep it going by providing additional confinement.
At 00:43-00:47 (end of footage) note the standing wave that has formed.
Books…Google-style
I think Google is going to show up at my apartment one day and digitize me. They are unstoppable.
A friend and colleague of mine was raving about GoogleBooks to me the other day, so I decided to give it a look. WARNING: be prepared to spend some time!
One of the nice things about this book search engine is that you can tell it to return “full view” books. Most of the newer books out there and probably most mainstream fiction is only available as a preview (which is useful in its own right).
But…if you search the “full view” books you can find some really neat things.
For example, I put in “Patagonia geology” as the search term and Darwin’s chronicles from the Beagle was right there!
So, this is great…perhaps you are one who makes yourself stay in your office and work instead of getting sidetracked by random books in the library. Well, now you can get even more sidetracked sitting at your desk.
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The book of life
Check out this article about a project to build an online archive of the Earth’s species.
“The Encyclopedia of Life will provide valuable biodiversity and conservation information to anyone, anywhere, at any time,” said Dr James Edwards, executive director of the $100m (£50m) project.
It is said to take 10 years or more to complete. Ideally, this will be a fantastic resource for both researchers and the general public.
The vast database will initially concentrate on animals, plants and fungi with microbes to follow. Fossil species may eventually be added.
That’s really cool! Especially with regards to this database as an educational tool, it will be nice for the general public to see both present and past species side-by-side.
Clastic Detritus 
