Till or glacial till is unsorted glacial sediment.
Till is derived from the erosion and entrainment of material by the moving ice of a glacier. It is deposited some distance down-ice to form terminal, lateral, medial and ground moraines.
Till or glacial till is unsorted glacial sediment.
Till is derived from the erosion and entrainment of material by the moving ice of a glacier. It is deposited some distance down-ice to form terminal, lateral, medial and ground moraines.
Sediment is a solid material made of loose particles that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation; if buried, they may eventually become sandstone and siltstone (sedimentary rocks) through lithification.
Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.
A moraine is any accumulation of unconsolidated debris (regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice sheet. It may consist of partly rounded particles ranging in size from boulders (in which case it is often referred to as boulder clay) down to gravel and sand, in a groundmass of finely-divided clayey material sometimes called glacial flour. Lateral moraines are those formed at the side of the ice flow, and terminal moraines are those formed at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines (till-covered areas forming sheets on flat or irregular topography) and medial moraines (moraines formed where two glaciers meet).
U-shaped valleys, also called trough valleys or glacial troughs, are formed by the process of glaciation. They are characteristic of mountain glaciation in particular. They have a characteristic U shape in cross-section, with steep, straight sides and a flat or rounded bottom (by contrast, valleys carved by rivers tend to be V-shaped in cross-section). Glaciated valleys are formed when a glacier travels across and down a slope, carving the valley by the action of scouring. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice, called glacial till or glacial erratic.
Examples of U-shaped valleys are found in mountainous regions throughout the world including the Andes, Alps, Caucasus Mountains, Himalaya, Rocky Mountains, New Zealand and the Scandinavian Mountains. They are found also in other major European mountains including the Carpathian Mountains, the Pyrenees, the Rila and Pirin mountains in Bulgaria, and the Scottish Highlands. A classic glacial trough is in Glacier National Park in Montana, USA in which the St. Mary River runs. Another well-known U-shaped valley is the Nant Ffrancon valley in Snowdonia, Wales.
The Illinoian Stage is the name used by Quaternary geologists in North America to designate the Penultimate Glacial Period c.191,000 to c.130,000 years ago, during the late Middle Pleistocene (Chibanian), when sediments comprising the Illinoian Glacial Lobe were deposited. It precedes the Sangamonian Stage (corresponding to the global Last Interglacial) and follows the Pre-Illinoian Stage in North America. The Illinoian Stage is defined as the period of geologic time during which the glacial tills and outwash, which comprise the bulk of the Glasford Formation, accumulated to create the Illinoian Glacial Lobe.
In geology, drift is a name for all sediment (clay, silt, sand, gravel, boulders) transported by a glacier and deposited directly by or from the ice, or by glacial meltwater. Drift is often subdivided into unstratified (unsorted) drift (glacial till) that forms moraines and stratified drift (glaciolacustrine and fluvioglacial sediments) that accumulates as stratified and sorted sediments in the form of outwash plains, eskers, kames, varves, and so forth. The term drift clay is a synonym for boulder clay. Both are archaic terms for glacial tills with a fine-grained matrix.
In the United Kingdom, drift is also applied as a general term for all surficial, unconsolidated, rock debris and sediment that is moved from one place to accumulate in another and mapped separately or otherwise differentiated from underlying bedrock. In this usage, drift includes a wide variety of deposits, e.g. loess, glacial till, river deposits, colluvium, and so forth, of Quaternary age. However, this term is most commonly used to specifically describe glacial deposits.
The Prairie Pothole Region (PPR) is an expansive area of the northern Great Plains that contains thousands of shallow wetlands known as potholes. These potholes are the result of glacier activity in the Wisconsin glaciation, which ended about 10,000 years ago. The decaying ice sheet left behind depressions formed by the uneven deposition of till as buried ice blocks melted in ground moraines. These depressions are called potholes, glacial potholes, kettles, or kettle lakes. They fill with water in the spring, creating wetlands, which range in duration from temporary to semi-permanent. The region covers an area of about 800,000 sq. km and expands across three Canadian provinces (Saskatchewan, Manitoba, and Alberta) and five U.S. states (Minnesota, Iowa, North and South Dakota, and Montana). The hydrology of the wetlands is variable, which results in long term productivity and biodiversity. The PPR is a prime spot during breeding and nesting season for millions of migrating waterfowl.
77°28′S 162°31′E / 77.467°S 162.517°E
The McMurdo Dry Valleys are a series of largely snow-free desert valleys on the continental coastline of Victoria Land, Antarctica, east of the East Antarctic Ice Sheet and west of McMurdo Sound and the Ross Sea. The Dry Valleys are notable for being the coldest and driest desert in the world, as well as being the largest ice-free region in Antarctica; as a result, the Valleys have become a notable hotbed for scientific research in the Antarctic region. The Dry Valleys' unique climate is due to their location nestled within the Transantarctic Mountains along with high-pressure katabatic winds that scour away snowfall and humidity across the region. Surrounding mountains prevent the flow of ice from nearby glaciers. The region's geology is primarily granites and gneisses, and glacial tills dot the bedrock landscape, with loose gravel covering the ground. The Valleys are one of the driest places on Earth, though there are several anecdotal accounts of rainfall within the Dry Valleys.
Suffosion is one of the two geological processes by which subsidence sinkholes or dolines are formed, the other being due to collapse of an underlying cave or void, with most sinkholes formed by the suffosion process. Suffosion sinkholes are normally associated with karst topography although they may form in other types of rock including chalk, gypsum and basalt. In the karst of the UK's Yorkshire Dales, numerous surface depressions known locally as "shakeholes" are the result of glacial till washing into fissures in the underlying limestone.