Signs of Erosion Hiking up to the High Drive

We were hiking (up, up, up) for our JASMER #2 cache (successfully, hurrah!), and although we were focused on our goal, we did take a significant amount of time to admire the scenery on our way up and down. This EC is a reflection of our observations. We hope you enjoy your time here!

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To complete this Earthcache (EC), please follow the well-marked trail from the parking lot, through GZ and up to the final WP. The area of focus is between GZ and the WP. This represents an elevation gain of approximately 100m.

Please read the questions you are being asked to answer, FIRST, before starting this EC.

Group responses are acceptable if each person in your party is clearly identified when answers are submitted. However, each person claiming a find must submit their own photo at the High Drive sign (final WP) with their log.

Due to nature of this EC, it must be completed during day light hours.

This is a seasonal cache and will be disabled in the winter months.

Please be sure to read the lesson, questions and send the answers using an in-game feature. I will read and respond to all submissions.

Enjoy this beautiful location!

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How Erosion Builds Mountains (source: Scientific American)

Mountains are created and shaped not only by the movements of the vast tectonic plates that make up Earth's exterior, but also by climate and erosion. In particular, the interactions between tectonic, climatic and erosional processes exert strong control over the shape and maximum height of mountains as well as the amount of time necessary to build--or destroy--a mountain range. Paradoxically, the shaping of mountains seems to depend as much on the destructive forces of erosion as on the constructive power of tectonics.

Because of the importance of mountain building in the evolution of Earth, these findings have significant implications for earth science. To a geologist, Earth's plains, canyons and, especially, mountains reveal the outline of the planets development over hundreds of millions of years. In this sprawling history, mountains indicate where events in or just below Earth's crust, such as the collisions of the tectonic plates, have thrust this surface layer skyward. Thus, mountains are the most visible manifestation of the powerful tectonic forces at work and the vast time spans over which those forces have operated.

The effort to understand mountain building has a long history. One of the first comprehensive models of how mountains evolve over time was the Geographic Cycle, published in 1899. This model proposed a hypothetical life cycle for mountain ranges, from a violent birth caused by a brief but powerful spasm of tectonic uplift to a gradual slide into "old age" caused by slow but persistent erosion. The beauty and logic of the Geographic Cycle persuaded nearly a century of geologists to overlook its overwhelming limitations.

In the 1960s the plate tectonics revolution explained how mountain building is driven by the horizontal movements of vast blocks of the lithosphere--the relatively cool and brittle part of Earth's exterior. According to this broad framework, internal heat energy shapes the planet's surface by compressing, heating and breaking the lithosphere, which varies in thickness from 100 kilometers or less below the oceans to 200 kilometers or more below the continents. The lithosphere is not a solid shell but is subdivided into dozens of plates. Driven by heat from below, these plates move with respect to one another, accounting for most of our worlds familiar surface features and phenomena, such as earthquakes, ocean basins and mountains.

Earth scientists have by no means discarded plate tectonics as a force in mountain building. Over the past few decades, however, they have come to the conclusion that mountains are best described not as the result of tectonics alone but rather as the products of a system that encompasses erosional and climatic processes in addition to tectonic ones and that has many complex linkages and feedbacks among those three components.

Convergence of tectonic plates generally occurs in one of two ways. One plate may slide down, or subduct, below the other, into the mantle. At a subduction zone boundary, the upper plate is thickened as a result of the compression and from magma being added by the melting of the descending plate. Many mountains, including almost all the ranges that surround the Pacific Ocean in a geologically active area known as the ring of fire, formed by subduction. With continental collision, on the other hand, neither plate subducts into the mantle, and therefore all the mass added as a result of the collision contributes to the building of mountains. Such collisions have created some spectacular topography, such as the Tibetan Plateau and the Himalayas, the mountain range that includes the worlds 10 highest peaks.

Climate and erosion

Erosion includes the disaggregation of bedrock, the stripping away of sediment from slopes and the transport of the sediment by rivers. The mix of erosional agents active on a particular landscape--gravity, water, wind and glacial ice--depends on the local climate, the steepness of the topography and the types of rock at or near the surface.

Climate is inextricably linked with erosion because it affects the average rate of material loss across a landscape. In general, wetter conditions favour faster rates of erosion; however, more moisture also promotes the growth of vegetation, which helps to "armor" the surface. Mountains in polar latitudes are the least vulnerable to erosion, partly because of the aridity of cold climates and partly because continental ice sheets such as those on Greenland and Antarctica commonly are frozen to the underlying rock and cause little erosion. In contrast, mountain glaciers such as those of the European Alps and the Sierra Nevada in California aggressively attack the subsurface rock, so that this type of glacier may be Earth's most potent erosional agent.

There are many other links among erosion, climate and topography. For example, mountains lift the winds that flow over them, causing increased precipitation on the range's windward slopes, intensifying erosion as a result. Known as orography, this effect is also responsible for the "rain shadow" that creates deserts on the leeward sides of many mountain ranges. Elevation can also affect erosion, because average temperature decreases with altitude, so that higher peaks are less likely to be protected by vegetation and more likely to be eroded by glaciers. In temperate regions, the rate of erosion is proportional to the average steepness of the topography, apparently because gravity- and water-driven processes are more effective on steeper slopes. Taken together, all these facts suggest that mountains evolve their own climates as they grow--becoming typically wetter, colder and characterized by more intense erosion.

Isostasy refers to the buoyancy of Earth's crust as it floats on the denser, fluidlike mantle below it. A mountain range, like any physical structure, must be supported, and it turns out that this support comes mainly from the strength of the crust and from isostasy. Under the soaring peaks of every mountain range is a buoyant "root" of crust that penetrates into the mantle. Continental crust is about 80 to 85 percent as dense as the mantle beneath, enabling crustal roots tens of kilometers deep to support mountains several kilometers high.

Isostasy is the key mechanism that links a mountains tectonic, or internal, evolution to its geomorphic, or external, development. When erosion at the surface removes mass, isostasy responds by lifting the entire mountain range up to replace about 80 percent of the mass removed. This uplift explains a number of phenomena that were puzzling before researchers fully appreciated the role of feedback in mountain building.

For example, high-precision surveys along the eastern margin of the U.S. have revealed that the land is rising at rates of a few millimeters to a few centimeters a century. Erosion that is concentrated at the bottom of river valleys may be especially significant because it can lift mountain peaks to elevations higher than the elevations before erosion started. This is possible because the removal of mass is localized (in the valleys), but the isostatic response lifts the entire mountain block, including both valleys and peaks.

Although isostasy can prop them up for many millions of years, landscapes without tectonic uplift do eventually succumb to erosion. Several studies have suggested that large areas of Australia are good examples of very old, decaying landscapes. These areas, which have not experienced tectonic uplift for hundreds of millions of years, are at most a few hundred meters above sea level. Their rates of surface uplift seem to be consistent with only isostatic response to erosion. In such tectonically active mountains as the Himalayas and the European Alps, measured uplift reflects a combination of tectonic driving forces and erosionally driven isostatic uplift. Given the rates at which mountains grow and then decay, we can infer that dozens of major mountain ranges have come and gone on Earth throughout its history.

Although relatively few of Earth's mountains are now believed to be in perfect equilibrium, many of them may have achieved such a balance at some time in their history. Mountain ranges, it appears, often go through three distinct phases. The first, formative stage begins with the converging of plates or some other tectonic event that thickens crust and causes topography to rise. During this stage, rates of uplift exceed those of erosion. Erosion rates increase dramatically, however, as elevations and relief increase. Depending on the size of the range and the local climate, uplift may persist until erosion rates or the strength of the crust limits the average elevation of the range from increasing any more. This is the second stage, a steady state that may continue as long as the rates of uplift and erosion remain equal. When uplift diminishes, erosion begins to dominate and the final stage begins. In this final stage, the average elevation of the mountain range begins a long, slow decline. The cycle may be interrupted or complicated at any stage by tectonic or climatic events as well as the feedback among those processes and erosion.

Examples Erosion Prevention Methods - there are others!

Revetments: an engineering technique used on a sloping surface or creating a sloping surface using stone, concrete or other material that creates a slope to absorb the energy of incoming water (click here);
Rock armour/riprap: large boulders placed in front of a cliff or slope to deflect (wave) energy away and protect from erosion (click here);
Gabions: a cage-like structure filled with rocks or concrete (click here).
Tree revetment is a river bank erosion control system that uses small fallen trees anchored horizontally in place along the river bank to prevent erosion. The trees slow the flow of water, which cuts back on the rate of erosion. They also catch sediment in the tree branches and prevent it from flowing down the river.
Coir logs are another erosion repair method made using coconut fiber. Coir logs are large in diameter, which makes them ideal for supporting river banks or being used for erosion control on hills, shorelines, and other areas prone to erosion. Even though they’re big, coir logs are easy to place. Once they’re in position, they can help establish vegetation growth. They’ve been effectively used in construction sites, restoration projects, and stabilization areas. Most coir logs will last two to five years before biodegrading. (click here)
Natural vegetation has a major impact on erosion. For the most part, slopes that have vegetation erode slower than those without. This is because the roots of the vegetation generally increase the soil’s strength, which makes it less prone to mass failure. Additionally, plants can act as shock absorbers during heavy rainfall, which also slows the rate of erosion.
Soil erosion mat: While these mats are sometimes made with wood fiber or straw, one of the top materials used is coir coconut fiber. This is because coir is strong yet natural. Plus, unlike straw or wood, coir can last in the wet conditions anywhere from two to five years. (click here for an image)

Sources/Additional Information:

Soil Erosion

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Questions - if you are delayed in sending your responses, please post a note. If sending responses for more than one cacher, clearly indicate the cachers' names in your submission; regardless, EACH cacher must post their own unique photo at GZ.

1. Required Photo for all cachers - to demonstrate that you were on site, post a photo of you/your caching name & date/your GPS/another caching object (etc.) in front of the High Drive sign (the final WP).

2. Based on your observations of Mays Peak and the surrounding area, identify an example (one of each) of how tectonic, erosional and climatic forces interact to shape these mountains. Please note that you are providing 3 distinct examples (one per category).

3. As you walk from GZ to the WP, identify 3 different examples of erosion prevention that you can observe between GZ and the posted WP.

4. Choose 1 method from your answer to Q4. To what extent is this method effective on Mays Peak and why?

Thanks for visiting and have fun!

Additional Waypoints

01ACPJP - High Drive Sign (stop here)
N 38° 48.028 W 104° 53.982
Required Photo for log...stop your observations by this point.
P0ACPJP - Parking lot
N 38° 47.431 W 104° 54.228
Porta-potties also available