Mississippi Delta

How could a series of pathological deltas be complete without including the Mississippi Delta?

The flashearth image is here and a diagram illustrating the pattern of delta lobe switching can be found here.

The pathologically curvy Rio Grande Delta

I spent a summer in college staring at maps and aerial photographs of the Rio Grande delta in Texas and Mexico. Maybe now I can get some use out of it.  I was working with J.D.  Stanley at the Smithsonian’s NMNH and he pointed me to the apparently high sinuosity of deltaic channels on the Texas side of the Rio Grande delta.

According to my notes, the modern Rio Grande has a sinuosity of 2.075 in its delta, while Holocene channels have a sinuosity of 1.83, younger Pleistocene channels have a sinuosity of 1.81 and remnants of older Pleistocene channels have about 1.32. So our data suggests that the channels of the Rio Grande delta have gotten curvier over time. I also did a literature review of channel sinuosity in other deltas and found that the Rio Grande was indeed anomalously sinuous compared to many of the world’s major deltas.  In my review, only the Niger and Klangat Langat deltas were curvier. Unfortunately, we never came up with a good mechanism to explain why the Rio Grande was so curvaceous.

Indeed, if you look at the flash earth images (http://www.flashearth.com/?lat=26.07433&lon=-97.526349&z=10.4&r=0&src=msa)  below, you can see what caught our eye. The first image shows the majority of the delta (look for the anthropogenically straightened main outlet channel), the next one zooms in on the modern river mouth and area just to the north, the third one shows a portion of the southern, Mexico portion of the delta, and the last one shows the northern portion of the delta, which if I recall correctly has some of the oldest exposed deltaic deposits along with some eolian features (which can been seen in the image).

Deltas in the Gulf of Corinth

The Gulf of Corinth is actively rifting, with the footwalls of large normal faults on the southern shore being uplifted by almost 1km in the last 2 million years or so(you can see some pretty spectacular striated fault scarps in the field). The combination of new and steep topography to be eroded, and a big linear hole in the ground to be filled, means that small deltas are building out into the Gulf pretty much all along its length. The variation in their size is due to differences in catchment area - the smaller deltas only being fed from the closest slopes, whereas the larger ones cut all the way through the mountains, probably in the gaps between different fault segments, and thus are supplied with much more sediment.

Understanding this interaction between faulting and sedimentation patterns is of great interest to petroleum geologists (arguably, this is what the North Sea looked like in the Triassic).

View on Flash Earth

Nearing the end...The Owyhee Map

I have spent many hours (while on family medical leave, no less) doing
the penultimate pass through the Owyhee map. Not only through the
detailed section but also out into the larger region from which the
lava flows originated.

Theses aren't the most beautiful snippets, but after one more pass,
the map will be nearly ready for external review. There is a chance
that Duane, Cooper, and I will do some additional fine-tuning of some
of the 'other' lava flows out there...you know, the ones we have
largely ignored, but are hugely important in the evolution of the
Owyhee system.

See the full gallery on posterous

Posted via email from Fresh Geologic Froth

The delta of Las Vegas Wash, Nevada: 2004-2008

The sad fact of the serious shrinkage of Lake Mead leads to the
neutral fact of the growth of tributary and mainstem deltas that feed
into the lake. The Colorado River's delta is an obvious example, but I
have gone for the delta of Las Vegas Wash in this post. LVW is an
ephemeral drainage that has 'gone all perennial on us' as a persistent
conduit of treated wastewater and an intermittent conduit of copious
amounts of storm runoff from mall and casino parking lots (among other
impermeable surfaces)

Turns out that the delta and the lake are also repositories for trends
in pharmaceutical use and abuse in Las Vegas...which is a little
creepy, no?

For an intro to the drug story, see:
http://toxics.usgs.gov/regional/emc/mead_vegas.html

For more on the delta (and some cool sonar stuff):
http://pubs.usgs.gov/of/2001/of01-070/index.html

The Nile Delta is a classic

The Nile Delta is a classic ((tags: delta, desert, fluvial))

I'm shocked that during this month ("April deltas bring May fold and thrust belts"), no one has yet posted images of the classic Nile River delta in Egypt.

This is the image that countless generations of geology instructors have shown students to show the fan-shaped map pattern of a delta. The fact the Nile cuts through a desert region makes for high contrast between its lush green and the Sahara on either side.

The Nile Delta is heavily developed; you'll find it spotted with light-colored loci of urbanity. Egypt's capital city, Cairo, is located right where the distributaries start branching out at the "base" of the fan-shaped delta.

NASA's Earth Observatory has some nice images you may want to consult, too. Like this one:
http://earthobservatory.nasa.gov/IOTD/view.php?id=7070
...and this huge-scale portrait of the delta:

Keep an eye peeled for crocodiles if you go visit via Flash Earth:
http://www.flashearth.com/?lat=30.82317&lon=30.969679&z=9&r=0&src=msa

Delta meets Dunes: Western Australia's Woomarel River

This particular river may very well be one of my favorites. The delta is nice and has multiple lobes in interesting arrangements amongst the sand dunes. In fact, the palimpsest fluvial patterns in the dune fields that flank the Woomarel River and the Gascoyne River to the North are nothing short of amazing. Not sure how I have missed these rivers for all these years.

Of course I know of the Woomarel River...but I will check it out anyway.

Gascoyne River, Western Australia

The Gascoyne River in Western Australia provides nice example of the importance of lobe-switiching / avulsion in the construction of some delta complexes. In this image (top of upper two images is West),  it is possible to discern at least 3 lobes. Go explore and find up to 6 (more?). Go upstream and see some spectacular aeolian v. river vignettes that show abandoned fluvial tracts overrun by dunes and one lobe that went astray and may not have met the sea... 

Wow! I love this place.

Must.see.this.

The wave-influenced Danube Delta

I'm loving the delta theme!

I couldn't resist posting the Danube, which is such a beautiful example of a wave-influenced delta. Check out the spit nicely showing the dominant wave direction. It's also worth comparing this essentially single-channel morphology to a highly distributary delta like the Lena that shows the scores of bifurcations and bifurcations upon bifurcations creating several hundred individual channels.

Permanent link to FlashEarth image: http://www.flashearth.com/?lat=44.877455&lon=29.44844&z=10.7&r=0&src=msa

Bombetoka Bay, Madagascar

Hunting for a Where on Google Earth location a while ago I ran across this wonderful tidally-influenced delta on the northwest coast of Madagascar. It is the mouth of the Betsiboka River and just north of the river mouth is the second largest port in Madagascar.

What struck me about the delta was not just the nice tug-of-war between riverine and tidal processes in shaping the islands, but the dramatic red color of the water in the Google Earth image (and others as well). This red color is symptomatic of the massive erosion resulting from rampant deforestation of the island.

The four photos are from Flash Earth, Google Earth, and the Gateway to Astronaut Photography, NASA Earth Observatory (ASTER satellite)

Flash earth permanent link: http://www.flashearth.com/?lat=-15.883853&lon=46.436067&z=10.8&r=0&src=msa

Astronaut Photograph: http://eol.jsc.nasa.gov/scripts/sseop/photo.pl?mission=ISS005&roll=E&frame=9418

Earth Observatory ASTER image: http://earthobservatory.nasa.gov/IOTD/view.php?id=5245

Colorado River Delta

Colorado River Delta ((tags: fluvial, delta, desert, earthquake))

It seems only fitting that we get a few snaps of the Colorado River Delta up here, since it was host to a large earthquake (7.2 magnitude) earlier this week.

NASA Earth Observatory agrees with this philosophy, and has posted one of their own:
http://earthobservatory.nasa.gov/IOTD/view.php?id=43416

...And Matthew von der Ahe reminded the geopathologists of this obvious next step in a comment on Ian's Lena River Delta post:
geopathology

So, here it is. The Colorado River Delta is an interesting place where the Colorado River used to pour into the Gulf of California (a.k.a. Sea of Cortez) in northwestern Mexico. The Gulf of California is a zone of fresh seafloor spreading associated with the transtensional nature of the North America-Pacific plate boundary in that area. The Baja California peninsula is essentially a freshly minted continental terrane, ripped off the west coast of Mexico by the relative motion of the Pacific Plate with respect to the North American Plate. The transtensional stress regime resolves itself into a series of pull-apart basins; low-lying areas in the continental crust. The Colorado River flows downhill, and as it flows, people siphon off water for use in agriculture or for drinking water. The volume of the Colorado River has been diminished to the point where only a fraction of its original discharge now makes it to the Gulf. In many years, no surface water at all can be seen completing the voyage to the river's mouth.

All right... let's go. I promise not to drink the water:
http://www.flashearth.com/?lat=31.951739&lon=-115.068966&z=9.8&r=0&src=msa

Lena Delta

One more Arctic delta for now. This is the Lena Delta. The flashearth image is here.  The you must, however, see this absolutely stunning landsat image.

Pechora Delta and Dyangylakh

Like Kyle, I think that all deltas a pathological, just some are more so. Particularly pathological are the Arctic deltas. Here are a couple more, the Pechora Delta entering the Barents Sea, and the island of Dyangylakh where the Olenyok River enters the Laptev Sea. 

Geologicheskiy and The Yenisey River Delta

I've been avoiding morphologies that show a strong signature of anthropogenic influence... I'm biased, I guess.  I'm not really surprised to find that deltas are very attractive to people and their messing around.  Fisheries, agriculture and shipping are all reasons that deltas. despite their susceptibility to flooding and shifting channels, are some very valuable ground to us humans.  The following are from the Yenisey River Delta, a river I'll admit I had never heard of before finding it in Flash Earth.  A little to the south of the delta, on a small tributary is a location labeled "Geologicheskiy."  I'm not seeing anything that looks like urbanization, and it has no listed population, so I'm not sure what is actually at this location.  Maybe it's just a cool rock.

OOOH!  I want a closer look!