Tag Archives: Central Arkansas

Geo-pic of the week: Aerial Photography

Aerial Photo-Central Arkansas

Sometimes the best way to see what’s on the ground is to get as far away from it as possible.  Geologists use a variety of tools to do just that.  One of those tools is aerial photography.

The picture above shows the Arkansas River where it leaves the mountainous western uplands and enters the bottomlands of the Mississippi Alluvial Plain, east of Little Rock (upper left).  Driving east across that boundary, it’s easy to get the impression that the Mississippi Alluvial Plain is a broad flat expanse of land with little to no distinguishing features.  That’s far from the case as this photo reveals.  

From high-altitude imagery, subtle relic features created by the Arkansas River can be easily recognized.  Note the swirling landforms that characterize the lowlands on the right side of the picture.  Over time the Arkansas River has meandered through the valley carving new channel courses and abandoning old reaches of channel.  The continually changing river has left a mosaic of oxbow lakes (water-filled abandoned channels) and arc-shaped river deposits known as point bars. 

Geo-pic of the week: Folded Rock In 3 Dimensions

 

folded rock together cross sectionfolded rock cross section close up

                                                         

Above are several images of the same rock sample: a highly deformed quartzose siltstone collected from the Womble Formation, Ouachita Mountains, Arkansas.  The uppermost image shows a cut and polished surface.  The green line that’s been added to the picture defines a fracture that split the sample after it was cut.  Ordinarily, that would be a bitter turn of events but, in this case, it was a fortunate accident.  The fracture provides a rare, multi-dimensional view inside a tightly folded rock (lower photo).  Luckily, the fracture propagated across the bedding rather than breaking along a bed, which makes the beds of the fold appear to fan out like a deck of cards showing a lot of the detail of the structure.