There's Too Much Tension

Transcription

1 There's Too Much Tension Once you find the geocache, click "Found It" on the Geocaching.com app and then read and answer the questions below. Make sure to return the cache to exactly the same place you found it for the next geocacher to find! Your address will be recorded when you submit this form. Not clemsongeopaths? Sign out * Required 1. Last Name, First Name * Water Tower at Kite Hill Tectonic Activity at Kite Hill Kite Hill is easily identified by the Clemson Water Tower on its top, visible from Highway 76. Geologists who have studied the rocks around Kite Hill suggest there was once an extensional fault in this area. Extensional faults, like the one found at Kite Hill, are formed by tension. The most common type of extensional fault is termed a normal fault. An active fault is one that is likely to experience movement. The Kite Hill fault is no longer active but some of its aftereffects can still be seen in the rocks scattered around the top of the hill. This tectonic activity originally occurred deep within the crust many millions of years ago and can only be seen now due to erosional processes that have removed the overlying cover and exposed the affected rocks. During a period of extension, portions of the earth s crust are forced apart. Often, such forcing generates a normal fault, or sometimes a shear zone (where the rocks are less brittle and do not break apart during movement). The example on Kite Hill represents a normal fault because the evidence suggests there were definite breakages, or pulling apart of the rocks. Magma (hot, liquid rock) that is rich in quartz tends to rise and fill these newly open spaces. It will then solidify or 'freeze' and form recognizable quartz crystals. This quartz will only form crystals when the cracks in the rocks are large enough to allow plenty of room for the crystals to grow. Fault Breccia 1/5

2 Fault breccia (pictured above) is formed in tectonic environments like Kite Hill. When an extensional fault is repeatedly activated, it grinds up the angular quartz crystals that were solidified previously in the cavities and incorporates these fragments into fresh magma moving in to fill the newly formed crack or void. Can you find any fault breccia in the area? Kite Hill & Regional Tectonics What is different about Kite Hill? Topographic maps illustrate three dimensional topography on a two dimensional map. On this map, the thin reddish brown lines are topographic contour lines. Each line connects points of equal elevation. As you can see, not every line is labeled with an elevation. In the map above, only the lines representing 700 feet and 800 feet above sea level are labeled, and are also thicker than the other 2/5

3 contour lines these are called index contours. If you count the number of lines between the 700 and 800 foot index contour lines, you should find there are 4. There is 100 feet between the two index contours (800 feet 700 feet), and there are four lines, therefore the amount of elevation increase for each line = 100 / 4 = 25 feet. That means the elevation change between two consecutive lines, also called the contour interval, is 25 feet. Kite Hill stands above the rest of campus, nestled between Highways 76 and 93. In the topographic map above, Kite Hill is shown in the center as the purple dot surrounded by concentric circles. These concentric, topographic contour lines indicate an increase in elevation (with the smallest circle marking the top of the hill), which should be apparent from where you are standing. 2. Using the contour line information from the topographic map above, what is the approximate elevation of Kite Hill? Hint: Remember the contour interval is 25 feet. * 725 feet 750 feet 850 feet 870 feet The rocks that underlie Kite Hill were likely formed as part of the large scale tectonic activity that formed the Appalachian Mountains. The most common rocks in the Clemson area are metamorphic specifically schist. Because Kite Hill is higher in elevation than the rest of campus, it is likely that something in the rocks here has slowed down the rates of weathering and erosion compared to the rest of campus. The large amounts of quartz present at Kite Hill are not typical of schist. This suggests that the rocks in the Clemson area are not uniform and that large scale features, like the Appalachian Mountains, are not uniform tectonic features, either. So, how exactly does this different mineral composition affect the rate of weathering? A geologist named S.S. Goldich developed a scale that predicts the stability of common minerals at the Earth's surface. Called the Goldich Dissolution Series, it places minerals in order from most stable to least stable. Use the chart below to answer the following questions. Goldich Dissolution Series 3/5

4 3. What mineral makes the rocks on Kite Hill more resistant to weathering than rocks in other areas of campus? * Plagioclase Biotite Amphibole Quartz 4. Which of the following gives the most probable explanation of how Kite Hill formed? * Erosion of the nearby Appalachian Mountains led to a large pile of loose sediment. A large volcano once existed here and the hill is all that is left. Fractured rock filled with quartz fragments resisted weathering. Compressive forces pushed rocks together to form the hill. 5. Search the area around the fence at the geocache to find pieces of fault breccia. What features in the rock led you to identify it as fault breccia? * Activity Evaluation 6. I enjoyed this activity. * 7. I learned something from this activity. * 4/5

5 8. This activity makes me want to learn more about this subject. * 9. Comments? (optional) Don't forget your geoselfie! Take a picture of yourself at Kite Hill with any fault breccia you can find and submit it via the link the follows after submission of this form. Powered by 5/5