A lesson about erosion
"Oh wow, look at that wall!" is exactly what I said when I stumbled upon this truly amazing geological feature while geocaching in the area. Notice how the path of the Cedar River has carved out and eroded the cliff wall on the other side. I was suprised when I discovered this that there was no EarthCaches in the area. This was an opportunity to place an EarthCache I just could not miss.
To log this cache you must answer the following questions:
1. What Type of erosion has created the present state of the cliff wall?
2. What causes the constant rate of falling pebbles from the cliff besides gravity?
3. Notice the patterns of color on the cliff wall, what caused this?
*Submit your answers to a google form with this link. Submiting your answers is REQUIRED and logs without submited answers will be deleted*
What is Erosion?
Erosion is the process of wearing away surface soil or rock by water, wind or other natural processes such glaciers, and then transporting it and depositing it elsewhere. Living things, like plants, animals, and even tiny bacteria also do their part. Everything we see on the earth's surface has been shaped by the forces of nature over very long periods of time.
Types of Erosion:
Rainfall and run-off create 4 types of erosion: Splash, Sheet, Rill and Gully Erosion:
- Splash Erosion: Small soil particles are detached and sent airborne through the impact of raindrops on soil.
- Sheet Erosion: Raindrops break apart the soil structure and it's moved down-slope by water that flows overland as a sheet rather than definitive channels. This occurs frequently during cloud bursts.
- Rill Erosion: Rills look like miniature gullys in a bank. Often seen where the bank of a road cut. The are usually no more than a few inches deep. Rill erosion develops small, short-lived, concentrated flow paths and occur where rain falls faster than it can soak into the soil.
- Gully Erosion: Water flows in narrow channels during or directly following heavy rains or melting snow. The gullies can erode to considerable depths.
Flowing water in rivers and streams causes Valley, Bank and Thermal Erosion:
- Valley or Stream Erosion: Continual water flow alongside land (along a linear feature) creates this type of erosion. It extends downward, deepening a valley, and head-ward, extending the valley into the hillside. This occurs most frequently in times of flooding.
- Bank Erosion: Over time, banks of rivers and streams are naturally worn down.
- Thermal Erosion: The result of melting and weakening permafrost due to flowing water.
Freezing and thawing: Cold weather causes water trapped in tiny rock cracks to freeze and expand, breaking the rock into several pieces.
Valley and Stream Erosion changes valleys over time:
We tend to think of the valleys and canyons around us as mute and unchanging and from the human time perspective very little change occurs. But in the longer view, from the perspective of geological time, the valleys change, evolve and grow. The inexorable force of erosion gouges the valleys deeper and wider and constantly gnaws away at the headlands to extend their length. On the other hand, sediment deposition clogs and changes the stream courses within the valleys where the stream flow slows and the gradient lessens.
A youthful valley has a “V” shaped cross section and the stream is at the bottom of the “V”. This valley at the portion of Soos Creek appears more mature and the valley is flat bottomed and several times wider than the creek. The Soos Creek valley along its lower reaches near the fish hatchery appears more youthful. The stream of a mature valley may occupy any position in the valley but typically flows along one side of the relatively flat-bottomed valley. The flat bottom of the mature valley is called a floodplain because it is usually underwater during the largest floods.
- EROSION OF YOUTHFUL TO MATURE VALLEYS, FROM ‘V’ SHAPED TO FLAT-BOTTOMED:
Please do not disturb the area. Damage to the site is unacceptable. Please be mindful of fragile ecosystems. EarthCache sites highlight the principle of collecting memories — not samples. Furthermore, no physical cache, or other items, can be left at the site.
DO NOT ATTEMPT TO CROSS THE RIVER!
This is an observation site only. You do not need to touch the cliff or get in the water. Doing so my be fatal as the river current is extremely fast and falling rocks are hazardous!
Source of information:
Erosion: various, including http://en.wikipedia.org/wiki/Erosion
