GSCI340 - Environmental Geology

The headaer showing the river is a good example of erosion by water. This example could also be describing sedementation by water.

The header that shows the red rock formations in the southwest U.S. is part of the Colorado Plateau. The Colorado Plateau spans 4 states: Colorado, New Mexico, Utah, and Arizona. The vast majority of the rocks are sedimentary, with some igneous deposits from dormant volcanos. Because of this, many fossils are found on the Colorado Plateau. Major rivers in the area are the Colorado River and the Green River.

sand dune header:

Sand dunes are built up ridges of sand over time, the small particles making dunes are usually composed of quartz. According to John Mangimeli (the Geology of Sand Dunes @ nps.gov) anything light enough to be moved by the wind can be called sand - so even snow falls in this category. The particles from rocks, are often eroded by the forces of water and ice, wind seems a secondary influence on the making of a dune. Wind moves finer particles in saltation (latin for jump), heavier particles are moved by surface creep when these smaller particles hit the heavier layers, causing their forward momentum.

The birth of a sand dune begins with a simple wind swept patch and further wind movement induces several types of “geomorphic” features and patterns. If arising from a single wind direction in its life time, a dune could be Barchanic ( a scattering of inverse horse shoe prints),Barchanoid (parallel wavy ridges), or Transverse (wavy parallel ridges).

Dunes formed from several wind directions take on singular to multi branched and even compound shapes because the opposing wind directions literally squeeze out a line (Linear dunes, or Reverse, when two linear drifts are pushed towards eachother) or make several arms (Star dunes)

The sand dune of the header appears to be Barchanic, wish there was an aerial view.

Source: Wikipidea & Geology of Sand Dunes by John Mangeli at nps.gov

*****wish i could edit my comment - Transverse dunes are obviously STRAIGHT parallel ridges, not wavy (which are the barchanoid)

The header with the cracked soil could be a great example of what land on the leeward side of a mountain, affected by a rain shadow effect, could potentially look like.

One of your headers is a photo of Mt. Rushmore in the Black Hills of South Dakota. This monument is composed mainly out of granite. The granite of the Black Hills was exposed during the Precambrium via erosion. However, this granite was later covered by sandstone, and once again exposed by erosion and tectonic plate uplift. The monument consists of sculptures of George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln.

-Wikipedia

This header is a pic of some sanddunes that illastrate the wind movement of sand in a rippling effect of the sand giveing the foot print of the direction of the ind current.

[…] number of GeoChallenges can be completed online in a reasonable amount of time (e.g., GeoChallenges #2, #3, and […]

This header is a picture of an angular unconformity which is younger sedimentary rocks located upon an erosion surface, below which older sedimentary rocks are tilted or folded. An unconformity is a significant break or gap in the geologic record. It is a time when erosion rather than deposition occured.

There is a header with a picture of lava on it. The type of lava that is present in the photo is Pahoehoe lava. The term “Pahoehoe” is derived from Hawaii meaning, “smooth, unbroken lava.” It is basaltic lava that has a somewhat pillow look to it and retains a temperature of about 1100 degrees celcius to 1200 degrees celsius. The flow of the lava typically advances as a series of small lobes and toes that continually break out from a cooled crust. This type of lava flow is low viscosity which in turn can form lava tubes. As the Pahoehoe lava flows away from the source the Pahoehoe can become a type of lava called aa.

There is one header showing a canyon with a winding river running through it. The canyon also has areas where it appears there was once water running and has since dried up. It is obvious that the river floods and at times flows high enough to refill the dried up river beds. The walls of the canyon also indicate that a lot of erosion occurs in this place. You can also see how the erosion has made the river deeper and shorter across.

The picture of the top of a hill that has a verticle striation pattern that has been weathered into it from falling snow that has frozen and melted over several decades. This along with rain has left an apparent smooth surface. These effects are apparent from the snow capped hill tops in the background and the water on the front at the bottom of the hill.

The header showing a beach is an example of how waves approach the shoreline. One can observe the effects of waves on the beach sand, such as sand particle motion in a uniform direction.

Also observable is the presence of rocks and gravel between the beach and green grass (a very small seacliff, perhaps). This is the result of erosion from waves and runoff.

I noticed algae growing on the beach sand. While detrimental to beach-goers, this algae may alleviate the overall erosion of the beach sand.

The header with the metamorphic rocks that shows a cross sectional view of is a good example of what happens to rock over time when it is under constant pressure and heat.

In one of the headers there is a picture of igneous rocks with columnar jointing. Within these rocks parallel, vertical columns are formed. Columnar jointing is caused when the rocks are weakened by lava cooling from the outside in.

One header showed a snow avalanche. Avalanches are a rapid downslope movement of ice and snow. Trees, rocks, and dirt also get mixed in at times. They are caused by weak spots in the snow and ice giving way with nothing downslope of them to resist initial movement, which “snowballs” into a much bigger phenomenon.