Snow On The Red Rocks
Jon Burch Photography
Photograph - Digital Capture
Looks like... Snow is precipitation in the form of flakes of crystalline water ice that fall from clouds. Since snow is composed of small ice particles, it is a granular material with an open and therefore soft structure, unless subjected to external pressure. Snowflakes come in a variety of sizes and shapes including types that fall in the form of a ball due to melting and refreezing, rather than a flake, and are known as hail, ice pellets or snow grains.
The process of precipitating snow is called snowfall and tends to form within regions of upward movement of air around a type of low-pressure system known as an extra tropical cyclone. Snow can fall toward the north and south poles of these systems' associated warm fronts and within their comma head precipitation patterns.
This type of precipitation occurs where relatively warm water bodies such as lakes are present. Because water evaporates from lakes, lake-effect snowfall becomes a concern downwind within the cold cyclonic flow around the backside of extra tropical cyclones. Lake-effect snowfall can be heavy locally and thunder snow is possible within a cyclone's comma head and lake effect precipitation bands. In mountainous areas, heavy snow is possible where upslope flow is maximized within windward sides of the terrain at higher elevations if the atmosphere is cold enough. Snowfall amount and its related liquid equivalent precipitation amount is measured using a variety of different rain gauges.
Once on the ground, snow can be categorized as powdery when light and fluffy, fresh when recent, or heavier and granular when it begins the cycle of melting and refreezing. Eventually snow forms into ice once it comes down, and after multiple melting and refreezing cycles forming a dense mass called a snow pack. When powdery, snow moves with the wind from the location where it originally landed, forming deposits called snowdrifts that may have a depth of several feet. After attaching itself to hillsides, blown snow can evolve into a snow slab causing an avalanche hazard on steep slopes. The existence of a snowpack keeps temperatures lower than they would be otherwise, as the white snow reflects greater amounts of sunlight, and any absorbed heat goes into melting the snow rather than increasing its temperature.
The water equivalent in snowfall is measured to monitor how much liquid is available to flood rivers from the melt water that will occur during the following spring. Snow cover can protect crops such as wheat, from the extreme cold. If the snowfall stays on the ground uninterrupted for a series of years, the snowpack develops into a mass of ice called glacier. Fresh snow absorbs sound, lowering ambient noise over a landscape due to the trapped air between snowflakes that attenuates vibration. These acoustic qualities quickly minimize and reverse, once a layer of freezing rain falls on top of snow cover producing a squeaking sound at low temperatures when walking across the top.
The red rocks of Sedona show layers of time in the rock strata. Defining the boundary between the Colorado Plateau to the north, the Basin and Range to the south and the base of the Mogollon Rim, Courthouse Butte, Bell Rock and the other red rocks form an escarpment that runs east-west through the middle of Arizona. The Mogollon Rim is about 200 miles long, and ranges between 2000 and 3000 feet in height. In the Sedona region, erosion has gradually eaten away at the rim, moving it northward a distance of about four miles and leaving behind some of the most spectacular and picturesque canyons and buttes found anywhere in the world.
The deep red color for which Sedona is famous is due to the presence of hematite or iron oxide, staining the sandstone of Schnebly Hill and Hermit Shale layers. The steep terrain is due the top layers of the strata being composed of basalt and limestone, which are both harder than the underlying sandstone. Water running off the edge of the escarpment dissolves the lower layers, creating the steep cliffs. Eventually enough soft material is broken down and eroded, undercutting the cap layer, subsequently breaking it off in large slabs allowing it to fall into the canyons. This process exposes new softer material and the process repeats, with the cliff face about twenty feet further north than it was before.
The red rocks themselves were formed by a layer of rock known as the Schnebly Hill Formation. Schnebly Hill is a thick layer of red to orange-colored sandstone, and a member of the Supai Group, which was deposited during the Permian Period about 299 to 251 million years ago. Approximately 800 to 1000 feet thick, Schnebly Hill is the major component of Sedona's well known "Red Rocks" visible in the area.
The Schnebly Hill formation is comprised of the Sycamore Pass and Bell Rock members, which are separated by a ten to twelve foot thick layer of grey-colored limestone called the Fort Apache Member, formed during a major incursion of an ancient Sea. There are no fossils in the Schnebly Hill sandstones, and virtually none in the thin limestone layers. - Wikki
Photograph copyright Jon Burch Photography
March 15th, 2013
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