Avalanche in Willow Creek Gulch Earthcache
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in our disclaimer.
This Idaho earthcache is ONLY available from Eastbound I-90. Do NOT attempt to access it from Westbound I-90! There is a full pulloff (though no restrooms) for cars and RVs/trailers.
Unfortunately, there are few exits in the vicinity, thus it would not be easy to “flip around” to access this cache. Give the kiddies or yourself a chance to stretch and learn something at the same time.
Logging Requirements:
Send the answers to #1-#6 to me through my geocaching profile (Since the advent of the "new" Message the Owner feature, I prefer messages through that venue).
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Location 1: Cords: 47 27.629 115 44.141
1. Facing Southwest (look to your left when standing between the signs) try to determine how far up the cliff the old railroad bridge was located based on the scaring still visible on the hillside. Describe what the scaring looks like.
2. Based on the information on avalanches listed above, what type of avalanche caused the destruction in this area? How did you come to this conclusion
3. What three minerals have been mined here with over 5 billion dollars worth mined to date (see signage)?
Location 2: 47 27.627 115 44.179
4. Measure the size of the boulder. At an average weight of 180 lbs per cubic foot, multiply length x width x height to measure this boulder. Based on the layers seen to your left (Southeast of these cords), match the TYPE of rock at your feet with the hillside and estimate how far up the hillside do you project that this bounder fell from.
5. In your estimation, how did the boulder likely end up at its current location on the valley floor?
6. (Per current gc.com guidelines, photos are no longer allowed to be required. HOWEVER they are encouraged, since they can help clarify that you have visited the location if your other logging requirement answers are vague). Take a picture of yourself and your GPSr somewhere at the pull off with something recognizable behind you that does NOT give away answers to other logging requirements.
History:
A spectacular avalanche, on Feb 10, 1903 swept away part of a Northern Pacific Railroad trestle that towered over the valley you are standing on. The trestle let NPR trains descend from this pass from 1890 to 1903.
As a result of the avalanche, that had wiped out the trestle and track, the train engine plunged 80 feet and was buried in 30 feet of snow; a passenger car dangled over open space; and a caboose with 8 people trapped inside dropped into a deep snowbank. Incredibly, no one was killed! After the accident, a new less hazardous trestle with a much slighter grade was erected by the Northern Pacific Railroad.
Geology:
The Bitterroot Mountains of this area are located on the eastern edge of the Idaho batholith. A batholith is a large exposed body of granite that is left exposed at the surface of the ground. Usually, these large bodies of granite are flat, largely due to glacial weathering. However, in this case, the granite was pushed up to form this very large and steep mountain range. Since the granite batholith was left behind, glaciers have eroded the granite, making the mountains even more grand. Add to that the action of large bodies of molten granite pushing up through the already rugged cliffs and you see the uniquely steep and precipitous mountains before you. The resulting range has several peaks over 10,000 feet, and in its northerly climate, some portions of this dramatic mountain range receive over 500” of snowfall.
Therefore, avalanches are a major part of the ongoing morphing of the mountains in Idaho. Avalanches are snow events where something triggers a reaction that results in a rapid flow of snow down a slope. These events are huge and can even trap air and water with the snow, creating a monstrous geological-altering event as ice, rocks, trees, and other material are torn from the mountain and descent the slopes to the bottom, often blocking streams and changing the topography of the surrounding hills.
There are several different types of avalanches. These classifications are based on:
• The type of snow involved
• The nature of the failure (what caused the snow to start sliding)
• What was the surface under the slide
• The mass of the flowing snow
All avalanches also share common elements: a trigger which causes the avalanche, a start zone from which the avalanche originates, a slide path along which the avalanche flows, a run out where the avalanche comes to rest, and a debris deposit which is the accumulated mass of the avalanched snow once it has come to rest.
Types of avalanches:
These categories are somewhat fluid, but tend to be summarized in one of four types:
• Loose Snow Avalanches – these usually occur early in the snow season with freshly fallen snow that has a light density. These usually occur on steep terrain. The trigger usually happens and one point and then spreads out down the slop as more and more snow is added. Visually, it forms a teardrop. These avalanches are usually rather compact and cover limit areas. Because of the light density of the snow, trees and rocks may survive this type of avalanche and the debris field will likely be small.
• Slab Avalanches – These are the avalanches that cause the most death and destruction. These happen late in the snow season, when there is a strong, cohesive layer of snow that has formed a compacted “slab.” Often, new snow is blown onto the top of a slab, usually on the leeward side of a slope, causing a shift in weight/pressure on the slab. Thus causing the slab to crack and fracture. This fracturing spreads quickly and soon huge slabs are rushing down the hillside. Because of their density and thus speed, they can trap boulders and trees (and people) and cause great damage in their wake. The debris field and scaring are evident for many years after the avalanche.
• Isothermal avalanches – these occur when packed snow becomes saturated with water. Thus they are usually a late-season event (during melt) and are not as extensive as Slab avalanches. Many are mostly water and act in a fashion similar to a flood. These avalanches tend to start at a point and spread out like a fan. Their debris field is small to medium and lies at the bottom of shallow slopes.
• Powder Snow Avalanches – These avalanches are the largest and most powerful of avalanches, with some of these exceeding speeds of 180 mph and carry 10 million tons of snow over long distances. These avalanches tend to flow along valley bottoms and event can go “uphill” for short distances. These avalanches usually start when a cloud of power snow falls over a cliff or precipice and mixes with air, dislodging underlying snow when it lands in the valley below. This resulting turbulence is called a gravity current.
As an additional geological note, mining since 1884 (and still active) in the area has resulted in 5 billion dollars worth of three important minerals (see logging requirement below) has made this area the largest producer of Silver in North and South America, with over 1 billion ounces of silver mined.
Congrads to Ben-san, Beadgal and RockhoundMT on FTF!
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Resources: Signage at the pull off
www.wikipedia.org “Avalanche”
Additional Hints
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