Warning: This in not a park and grab. Read the description below, but basically you need to:
1. Get out of the car and look at how the boulder affected line of the creek bank on the east side of the road (erosion).
2. Measure the size of the rock..
3. Measure the changes in the valley ("creek bank") due to the boulder.
All earthcaches are educational and there is a lot to do here – reading, activities and questions. You must do the activities below to answer the required questions. Most people will feel they have earned all those stars.
Educational objectives of this earthcache:
1. Look at different types of erosion.
2. Learn about valley and stream erosion.
3. Observe the glacial erratic along the edge of the valley and how it affects erosion and how much.
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:
Soos Creek drains about 70 square miles of land but the part of Soos Creek near this earthcache is only the upper portion of the watershed. This earthcache is on the edge of 146th Avenue SE which runs parallel to the edge of the valley created by erosion above Soos Creek and a glacial erratic boulder is located at the edge of the bank.
- SOOS CREEK:
- SOOS CREEK TRAIL:
ACTIVITIES TO BE DONE ONSITE:
Stay on the area of the shoulder of the road. The boulder itself is on common area property owned by the neighborhood. Respect their property and do not climb on the boulder or go around it, not that you would want to plow through the blackberry bushes anyway.
1. Measure the Change in Erosion: Face the boulder and look to the left and notice the line of erosion defined by the top of the bank in the north-south direction (parallel to the road). Note that it changes as it approaches the area of the boulder. Measure or estimate, in feet, how far the boulder affected the erosion of the valley. To measure, you might stand facing the boulder and then go to your left and measure the distance from the edge of the road to the drop off, then go over to the right of the boulder and measure the distance from the edge of the road to the drop-off. Let me know the difference and if you are measuring in feet, meters, or steps. Optional: also think about including the far side of the rock in the amount erosion has been retarded.)
2. Measure the size of the rock: Stand on the shoulder of the road opposite one side of the rock (it might be blocked by a small tree) and note or mark the location, then stand on the shoulder opposite the other side of the rock and note that location. Measure between the 2 spots in FEET. This is the LENGTH of the rock. You can’t measure the width but it’s about the same so use the same number. Estimate the HEIGHT of the rock (maybe imagine a 6’ tall man standing by the rock). Include what part of the rock you think might be buried.
3. Approximate the weight of the rock, in tons:
Use Thickness = height times 2 (height from your feet to the top times 2)
Use this formula, it’s explained in the reference section at the end:
If measuring in feet, use this formula:
Weight in tons = Length x Width x Thickness / 23
(multiply length (in feet) times width times thickness and divide by 23)
If measuring in meters, use this formula:
Weight in tons = Length x Width x Thickness x 1.66
(multiply length (in meters) times width times thickness times 1.66)
Note: the curb weight of a new Jeep Wrangler is about 2 tons (the 4-door version is more.)
To claim this earthcache, you MUST do the activities above and answer the questions below and email the answers about the same time you claim your find. If you don’t get questions 2 and 6, I will assume you didn’t do the activities, are an armchair cacher, and I will delete your log.
1. Start your email with the name of the cache and number of people in your party, and their geocaching names if they have separate accounts.
2. How much has the boulder affected the erosion of the bank? (in feet) (hint: face the rock and look to the left along the top of the bank to the north. It is roughly parallel to the road. How far from the boulder would that line pass if the boulder had never been there?) (I’m now accepting this in either feet or steps. If kid steps, maybe say the age of the child also.)
3. What type of erosion formed the bank you saw on the left when you faced the rock? Rill erosion, gully erosion, valley/stream erosion, thermal erosion, or ???
4. Name 2 characteristics that identify this valley as a mature valley.
5. Do you think it would it be practical to collect rocks like this and put them along the Green River to stop erosion. Yes or No. Why? (keep it simple).
6. How big is the rock? What is the weight of the boulder? (hint: see activity 2 above). If not sure of your math, include your dimensions in your email.
7. How does the weight compare to that of a Jeep. (hint: Jeep weight in description above)
Sources:
Soos Creek: http://www.ecy.wa.gov/programs/wq/tmdl/SoosCrTMDL.html
and http://buckwoody.wordpress.com/2013/10/26/king-county-trails-series-soos-creek-trail/
Erosion: various, including http://en.wikipedia.org/wiki/Erosion
Riprap: http://en.wikipedia.org/wiki/Riprap
Volume of spheres, ellipsoids and ovoids: http://en.wikipedia.org/wiki/Ellipsoid
Weight of granite: http://www.pyramidgranite.com/pages/faqs.html
and http://www.reade.com/resources/reference-charts-particle-property-briefings/89-weight-per-cubic-foot-and-specific-gravity-metals-minerals-organics-inorganics-ceraqmics
and http://www.engineeringtoolbox.com/density-solids-d_1265.html
Jeep: http://www.motortrend.com/cars/2014/jeep/wrangler/specifications/exterior.html
Other: http://galleryhip.com/stream-erosion-diagram.html
Other: http://www.watersheds.org/earth/morevalley.htm
Reference:
(Optional math: assume the rock is a perfect ellipsoid and use the radii of the rock, weight of granite is 168 pounds per cu. Ft, and 2,000 pounds per ton, and Pi is just Pi:
The formula is 4/3 x Pi x r1 x r2 x r3.)