Here is a second image from the Tanezrouft showing multiple folding of Palaeozoic sediments. It also shows a number of water gaps through the cuestas.
The flashearth image is here. It was also Ron's choice for Where on (Google) Earth #66.
The Algerian Tanezrouft ('Land of Terror') Basin is a classic area of geopathological geomorphology. Any part of it produces stunning images. Japan's ALOS remote image looks like modern art. Deflation by the wind exposes these shallow periclinal synclinal basins in Palaeozoic rocks.
The flashearth image, a good place to start exploring this wonderful place is here.
The Paw Paw Bends: entrenched meanders along the Potomac River
The Paw Paw Bends: entrenched meanders along the Potomac River ((tags: appalachian, fluvial, mountain belt))
You don't have to go all the way to Kazakhstan for nice examples of entrenched meanders. In fact, there is a sweet set along the Potomac River in the Valley & Ridge physiographic province of the Appalachian mountain belt. These meanders are named for the nearby town of Paw Paw, West Virginia. While that sounds like the most hick name imaginable, it's actually named after a local tree with surprisingly tasty fruits.
The Paw Paw Bends (39.5836 Lat, -79.3986 Long) were the site of an extremely costly mistake on the part of the Chesapeake and Ohio Canal, which otherwise follows the north bank of the Potomac River with high fidelity. However, because of the sinuous course of the river here, Canal engineers decided to dig a 3/5-mile-long tunnel through a nearby ridge as a shortcut. Unfortunately, the highly folded Brallier Shale (Devonian) that made up the mountain's interior collapsed repeatedly and constantly, retarding the progress of the entire Canal. The tunnel took 14 years to complete, a delay that doomed the Canal to obsolescence (in favor of the railroad).
This is a spectacular example of an entrenched meander in a gorge that cuts through a sequence of tightly folded sedimentary rocks. This is near Karagandy, Kazakhstan, approximately N47E66. I have no other details, but the discontinuous channel pattern within the gorge is intriguing as well. There is no end of interesting geomorphology in Kazakhstan. Anyone have any details about this area?
This image shows evidence of the rapid neotectonic uplift of the Coastal Cordillera of Northern Chile. This area is being uplifted by 'flat slab' subduction of a buoyant aseismic ridge on the Nazca plate beneath the Chilean margin. First, note the steep sea cliffs showing the rapid uplift, and a dendritic tributary stream network feeding a coastal alluvial fan in the bottom right of the image. Second, on the salar itself, can be seen the scarp of a normal fault, the outcrop of which can be traced to the left of the image. There are several normal fault scarps on the surface of this salt flat but this is the most obvious.
The image can be found on flashearth here.
This is one of the many alluvial fans on the western flank of the Andean thrust forearc north of Antofagasta, Chile, but one with the most classical delta shape. It is near Quillagua and can be found on flashearth here.
Thoroughfare Gap, VA
Thoroughfare Gap, VA ((tags: water gap, fluvial, mountain belt, appalachian))
Thoroughfare Gap, Virginia (38.8224 Lat, -77.7132 Long) is a prominent water gap in the Appalachian mountain belt. Broad Run has created a classic V-shaped water gap in the long linear trend of the Bull Run Mountains. This location is the eastern margin of the Blue Ridge physiographic province, where it meets the western edge of the Triassic-Jurassic Culpeper Basin of the Piedmont physiographic province. A close look reveals three north-south-trending ridges in the mountains: these are the more resistant layers within the Cambrian Chilhowee Group, a transgressive sequence draped atop the Blue Ridge's basement massif. The overall structure of the Blue Ridge is an anticlinorium; here at the eastern margin, the bedding dips to the east.
If you visit this area, the best parking will be found on Route 55, at the Broad Run post office, just east of the narrowest part of the gap. Besides Route 55 (and Broad Run), Interstate 66 squeezes through, and a railroad line as well. Natural gateways like Thoroghfare Gap have been fundamental pathways for human migrations since humans populated this area. You could even say that gaps like this one were very tempting to turn into... thoroughfares. The charismatic, towering Chapman's Mill is also located at this gap: http://www.chapmansmill.org/
Harpers Ferry Water Gap: WV, MD, and VA
Harper's Ferry, West Virginia (39.32496 Lat, -77.73644 Long), sits at the confluence of the Potomac River and Shenandoah River, right upstream of where they flow east across two resistant ridges of rock. This double water gap marks the spot where the river exits the Valley & Ridge physiographic province and enters the Blue Ridge physiographic province. The stratigraphic column of the Blue Ridge is doubled by faulting, and the river has to trek twice over its most resistant layers. From Harper's Ferry, looking east, the two water gaps look like a gunsight. Harper's Ferry is also one of the seminal locations of action that triggered the Civil War: it was here that John Brown made his raid on the armory. Here's an historical photo, looking over Harper's Ferry itself, east towards the rivers as they flow through the first gap:
(Largely) Recessional shorelines and trapped playas, Spring Valley, NV
This image of the north end of Spring Valley shows an markedly elaborate array of late Quaternary pluvial lake shorelines. It also reveals some details about how an ephemeral drainage network develops in this odd topographic setting. Think 'champagne fountain' for the area in the lower right hand corner. The largest playa in the image, 'Big Hard Pan', is a spot where I used to take the UNR field camp for impromptu frisbee games. It also is the source of the funniest 7.5 Quad name in Nevada.
A desert stream 'goes all distributary on us' in a huge dune field
near Tongguzbasti, China. An amazing scene.
I pulled this image from Flash Earth because I was struck by: the
spectacular folds in the rocks and the juxtaposition of a sediment-
laden ephemeral drainage network. Superposed drainage? Downstream
spill?
What and why...
While randomly perusing Google Earth to find an image suitable for Where on (Google) Earth #182, I became re-enamored with the staggering array of complex and bizarre assemblages of landforms and landscapes on our planet. In particular, I find that the world's deserts are rife with landscapes and landform assemblages that approach the pathological* in their patterns and characteristics. But pathological landscapes are not the sole domain of the desert, they are azonal phenomena that occur across the planetary surface.
*pathological in the sense of being developed or expressed in such a degree that is extreme, excessive, or markedly abnormal.
The point of this blog is to develop an image catalog of such landscapes as well as constituent landforms, deposits, and processes that comprise and underlie them. Thus, the images can be derived from screen captures drawn from Google Earth, Flash Earth, Bing Maps, Google Maps, or your favorite GIS program. Field photographs of notably 'pathological' deposits or landforms are certainly appropriate as well.
We have all seen and, likely purchased, atlases of satellite imagery that emphasize the sheer beauty as well as weirdness of landscapes as seen from space. Now, with virtual globes, geobrowsers, and various GIS programs, we can break the constraints provided by the selection of images in those books and look anywhere we want to find intriguing visions of the Earth's surface.
Ideally, this blog will become a group effort with several contributors. In reality it may just stay one of my many side projects. I truly hope for the former, but won't mind the latter.
The only rules: provide the coordinates of the approximate center of the image; tag it by process[es] or deposit type[s]. Provide an extremely brief description of what is going on...not treatises here, just a brief description. Leave it to the interested viewer to explore the area of the image and come to terms with its scale...or provide a scale. The idea, however, is to not dwell too long on posting an image.
Here are some obvious tags: fluvial, aeolian, glacial, coastal, karst, thermal, mass wasting, erosion, anthro, tectonic, etc. Note that too many tags compromises clarity to some extent.
SR 410 Nile Valley Landslide (west of Naches), originally uploaded by Washington State Dept of Transportation.
Check out the great photoset of the recent landslide near Naches, Washington.
Impressive lava-river interaction in Argentina
Some images from Google Earth and Google Maps of an area of significant lava and river interaction in Argentina. Field Trip! The center of the image is approximately 36.40 S, 69.42 W.
This site was discussed in the following talk:
GEOMORPHIC HISTORY OF RIVERS DRAINING THE EASTERN ANDEAN CORDILLERA (34–37°S) CONSTRAINED BY TEPHROCHRONOLOGY, U-SERIES DATING OF PEDOGENIC CARBONATE AND COSMOGENIC 3HE DATING OF BASALT FLOWS
HYNEK, Scott A., Geology and Geophysics, University of Utah, 115 S 1460 E, Salt Lake City, UT 84112-0119, scott.hynek@utah.edu, MARCHETTI, David W., Geology Program, Western State College of Colorado, 600 N. Adams St, Gunnison, CO 81231, FERNANDEZ, Diego P., Geology and Geophysics, University of Utah, 115 S. 1460 E. Rm 383, Salt Lake City, UT 84112, and CERLING, Thure E., Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112Alluvial deposits and associated geomorphic features are dated by their relation with volcanic rocks. The age range and geologic setting requires a broad approach to constraining the history of rivers draining the Cordillera. Maximum age estimates are provided by identification of the ~ 450 ka Diamante Tuff in fill terraces. Along the Río Diamante this ash bed is observed >100 m above modern river level. In the Río Papagayos and Río Atuel drainages, the Diamante Tuff is associated with alluvial surfaces much closer to modern river level. Coarse Diamante pumice in the Río Atuel implies significant changes to the headwater drainage system since 450 ka. The maximum age constraint implied by occurrence of the Diamante Tuff in fill terraces has been successfully combined with minimum age estimates from cosmogenic 10Be approaching 350 ka (Baker et al., 2009). The relatively old age of alluvial surfaces in the region is additionally supported by U-series age estimates derived from pedogenic carbonate in volcanic soils. A minimum age in excess of 100 ka is conservative. The dated surface is underlain by a pumice/lapilli tephra deposit and basalt flows both of which have the potential to provide maximum age estimates for the surface. Conversely, the U-series data implies that the basaltic volcanism is older than 100 ka. Our age estimates of flows in several drainages are much younger. Cosmogenic 3He concentrations in hornblende from basaltic-andesites erupted along the Río Salado indicate exposure, and therefore eruption, ages younger than ~ 6 ka. These flows temporarily dammed the Río Salado in one location and bedrock incision below the level of the flows has occurred since. 3He concentrations in olivine from basaltic rocks at northeastern Volcán Payún Matru indicate a shield-building phase at ~ 40 ka. Recent basaltic aa flows from multiple vents are morphologically quite young and 3He exposure ages are forthcoming for one of them. The Río Grande has incised the older flows, and provides an average incision rate over a full glacial cycle. Combination of geochronological data from the region indicates provides accurate, if not tightly constrained, ages for alluvial surfaces and identifies spatially variable geomorphic rates influenced, in part, by contemporaneous volcanism.
Posted via email from Fresh Geologic Froth
Lava v. River example from British Columbia
Kathy C. turned me on to this example yesterday. I had no idea. Lava flow is only about 250 yrs old. It is in the Stikine Volcanic Field. There is a related, somewhat brief, paper:
Roberts, M.C. and McCuaig, S.J., 2001, Geomorphic responses to the sudden blocking of a fluvial system: Aiyansh lava flow, northwest British Columbia. The Canadian Geographer, v. 45, n. 2, p. 319-323.
The vent is located at 55.11 N, 128.89 W.
Field trip!
Posted via email from Arbitrary Frothings
Submerged tree in Clear Lake, Oregon
This underwater picture shows a lone submerged tree in Clear Lake, OR.
There are many more than this. One (maybe most) date to about 2700 yrs
bp when a lava dam blocked the McKenzie River. Freezing water,
exceptionally clear.
Posted via email from Fresh Geologic Froth
Intracanyon lava flows: Does the river give a dam?
Check out this SlideShare Presentation: 
Distilling LiDAR data with ArcGIS
Turns out that ArcMap has some very useful tools buried in the toolbox for evaluating the basic characteristics of LiDAR data. For example, using the 3D analyst extension, it is possible to collate the basic parameters of *.LAS tile sets. For example, the following steps:
3d analyst > conversion > from file > point file information
will generate a polygon shape file of the data tiles and will atrribute each tile set with measures of point count, point spacing, max z, min z, etc. This is useful because it is nice to have a simple polygon file that shows the extent of the data and some of the metrics in the attribute table are important to have for applying other types of processing to the data. In the figure above, the tiles are labeled according to object id (OID) rather than filename because the filenames are exceedingly cumbersome.
Posted via email from Fresh Geologic Froth
