Geologic Formations. More recent Quaternary age rocks are found in glacial deposits from the Pleistocene and Holocene eras and recent alluvial gravel deposits, present along Glacier’s extensive stream and river network. Landslide deposits are also prevalent in recent sediments due to the incredible relief in the park.
the boundary between these two altitudinal zones of a glacier is an irregular line which marks the highest point at which the glacier's winter snow cover is lost during melt season. the position of this line on the glacier is an indication of whether a glacier has a positive or negative budget.
Glacier Movement. A valley glacier has various components of flow. First, the entire glacier moves as a single mass over the underlying rock surface. The pressure from the weight of the glacier generates a layer of water that helps the ice glacier move downslope. This process is called basal sliding.
Just as the base of a glacier moves slower than the surface, the edges, which are more affected by friction along the channel walls, also move slower.
Firn line. A line across the glacier, from edge to edge, that marks the transition between exposed glacier ice (below) and the snow-covered surface of a glacier (right).
As glaciers carve U-shaped valleys, rocks plucked from the bedrock and frozen in the ice etch grooves and striations in the bedrock. Rocks scoured from surrounding valley walls create dark debris lines called lateral or medial moraines along the edges and down the center of glaciers.
Longitudinal surface structures (may be called longitudinal foliation or flow stripes) are common on glaciers and have a planar or layered structure that develops in ice during ice flow. The layers are characterised by variations in the ice crystals (e.g., coarse-clear and white bubble-rich).
A lateral moraine forms along the sides of a glacier. As the glacier scrapes along, it tears off rock and soil from both sides of its path. This material is deposited as lateral moraine at the top of the glacier's edges. Lateral moraines are usually found in matching ridges on either side of the glacier.
The yellow, black and brown stripes occasionally seen are formed in glaciers as the moving ice sheet picks up dirt and sediment on its way to the sea.
Last but not least, there are striped icebergs, which are also unique to Antarctica. These are created by the intrusion of seawater into vertical cracks, which occur in the ice shelf as it breaks away from land. As seawater floods up to fill cracks in the cold, light-coloured glacier ice, it freezes into a dark stripe.
Anatomy of a Glacier Definitions The accumulation (input) zone is where a glacier gains snow and ice through snowfall and compression. Ice begins to flow like a conveyor belt, driven by gravity and ever mounting snows. In the lower region or ablation (output) zone, the glacier loses ice through melting and evaporation.
As the glaciers expand, due to their accumulating weight of snow and ice they crush and abrade scour surfaces rocks and bedrock. The resulting erosional landforms include striations, cirques, glacial horns, arêtes, trim lines, U-shaped valleys, roches moutonnées, overdeepenings and hanging valleys.
The top layer is snow that thickens further up the glacier. Below this layer is firn, a transitional layer between snow and ice, which is as hard as ice but not as dense. The deepest layer is ice. The snow and firn are thickest at the top of the glacier and thin down-glacier to zero at the equilbrium line.
A moraine is a ridge-shaped mound of till that forms as a glacier recedes. There are different types of moraines that are named depending on which part of the glacier the sediment comes from.
PluckingErosion by Glaciers Plucking is the process in which rocks and other sediments are picked up by a glacier. The sediments freeze to the bottom of the glacier and are carried away by the flowing ice.
Glacial deposition is the settling of sediments left behind by a moving glacier. As glaciers move over the land, they pick up sediments and rocks. The mixture of unsorted sediment deposits carried by the glacier is called glacial till. Piles of till deposited along the edges of past glaciers are called moraines.
Movement of ice sheets. An ice sheet moves downslope in a number of directions from a central area of high altitude and is not restricted to a channel or valley. The ice sheet must expand because of the constant accumulation of ice and snow.
The central and upper portions of a glacier, as do those portions of a stream, flow more quickly than those near the bottom and sides, where friction between the ice and valley walls slows down the flow. In general, the rate of plastic flow is greater than the rate of basal sliding.
Glaciers in temperate zones tend to move the most quickly because the ice along the base of the glacier can melt and lubricate the surface. Other factors that affect the velocity of a glacier include the roughness of the rock surface (friction), the amount of meltwater, and the weight of the glacier. Basal sliding and plastic flow.
Basal sliding and plastic flow. A valley glacier has various components of flow. First, the entire glacier moves as a single mass over the underlying rock surface. The pressure from the weight of the glacier generates a layer of water that helps the ice glacier move downslope. This process is called basal sliding.
Ice sheets do not move as quickly as alpine glaciers because there is less slope and more mass involved. Ice sheets move mostly by plastic flow. Mountain ranges are completely buried by the ice sheet at the South Pole, which is greater than 3,000 meters thick. Movement of valley glaciers. Glaciers can move more than 15 meters a day.
Glaciers can move more than 15 meters a day. The larger volumes of ice on steeper slopes move more quickly than the ice on the more gentle slopes farther down the valley. These dynamics allow a glacier to replenish the ice that is lost in the zone of wastage.
This more rigid upper zone, which is called the zone of fracture, is carried along the top of the plastic flow piggyback style. Sometimes the zone of fracture moves faster than the underlying plastic flow. When this happens, especially down a steep slope, the surface breaks into a series of deep fissures called crevasses.
Uplift of the Colorado Plateau was a key step in the eventual formation of Grand Canyon. The action of plate tectonics lifted the rocks high and flat, creating a plateau through which the Colorado River could cut down. The way in which the uplift of the Colorado Plateau occurred is puzzling.
Instead of subducting at the usual steep angle, the Farallon Plate probably subducted at a shallower angle and a faster rate. Shallow-angle subduction allowed for deformation to move further inward from the plate margin – about 625 miles.
The story of how Grand Canyon came to be begins with the formation of the layers and layers of rock that the canyon winds through. The story begins about 2 billion years ago when igneous and metamorphic rocks were formed. Then, layer upon layer of sedimentary rocks were laid on top of these basement rocks. To look at rock layers, geologists use ...
Finally, beginning just 5-6 million years ago, the Colorado River began to carve its way downward. Further erosion by tributary streams led to the canyon’s widening. Still today these forces of nature are at work slowly deepening and widening the Grand Canyon.
Then, between 70 and 30 million years ago , through the action of plate tectonics, the whole region was uplifted, resulting in the high and relatively flat Colorado Plateau.
Grand Canyon is the result of a distinct and ordered combination of geologic events. The story begins almost two billion years ago with the formation of the igneous and metamorphic rocks of the inner gorge. Above these old rocks lie layer upon layer of sedimentary rock, each telling a unique part of the environmental history ...
Numerous normal faults cut across Grand Canyon. Normal faults form in response to extensional tectonics or in other words when a region is being slowly pulled apart, eventually resulting in a landscape such as Nevada’s basin and range.
Common Belt series rocks found in Glacier include the Appekuny, Prichard, Grinnell, and Snowslip Formations. Reddish-brown and greenish-gray in appearance, these rocks are comprised of argillite and quartzite material that was compressed under sea water to form mudstones.
The origin of Belt series sedimentary rocks dates from about 1,600 to 800 million years ago. Common Belt series rocks found in Glacier include the Appekuny, Prichard, Grinnell, and Snowslip Formations.
Stromatolites, ancient fossils of blue-green algae that provide evidence of earth’s earliest physical and chemical compositions, are found in these calcareous settings and record the only trace of Proterozoic life known in the Belt Sea. The diorite sill is a 30 to 100 meter thick intrusion within the Helena formation.
The diorite sill is a 30 to 100 meter thick intrusion within the Helena formation. A highly recognizable feature, the sill is a dark-banded, horizontal layer running through the pale gray Helena formation rocks. Cretaceous age rocks formed in outcrops along the east and south edge of Glacier some 70 to 100 million years ago.