Parts of a Glacier Division A Study Guide- Part 2 Zones of a glacier Zone of Accumulation: The region where snowfall adds ice to the glacier. It occurs where the temperature remains cold enough year-round so that winter snow does not melt or sublimate away entirely during the summer. Zone of Ablation: The region where ablation subtracts ice from the glacier through melting or sublimation. Equilibrium Line: A boundary between the zone of accumulation and ablation controlled by elevation and latitude. Head: The uphill, top end of a glacier. Terminus: The downhill, bottom end of a glacier. Snowline: The area between the summer melting and accumulation area where the snow lasts from season to season. Brittle Zone: Crevasses are common in this zone. Brittle-Plastic Transition (dotted line): A line between the brittle and plastic zones at about 60m. Deep, because ice cannot crack below that. Plastic Zone: Ice cannot crack in this zone.
Types of moraines Glacial Moraine: A stripe of debris or sediment dropped by a glacier. Lateral Moraine:A stripe of debris along the side of a glacier from sediment dropped on the glaciers surface from its edge. Medial Moraine: A stripe of debris in a glacier constituting two lateral moraines from when two valley glaciers merge. End/Terminal Moraine: A stripe of sediment accumulated at a glacier s toe that has been built up. Recessional Moraine: A secondary terminal moraine deposited during a temporary glacial standstill during its retreat. Ground Moraine: An accumulation of lodgment till at the base of the ice deposited as the glacier retreats. They often form small hills or plains and may be turned into a drumlin by overriding ice. Ice within a glacier Fresh Snow: It contains up to 90% air and is very loosely packed. Its density is about 0.1 g/cm 3 Firn: It is snow that persists for an entire year and has a density of about 0.6 g/cm 3 Glacial Ice: It forms at a depth of about 50 meters deep and has a density of about 0.9 g/cm 3
Characteristics of a glacier Pyramidal Peak (1): It is a sharp, triangle shaped peak with the faces separated by ridges. Arête (2): It is a sharp ridge between two cirques of corries. Cirque/Corrie (3): It is a bowl-shaped hollow with steep sides and back filled with ice. Tarn (4): It is when a lake forms in a in the floor of a cirque. Alluvial Fan (5): It is a fan shaped pile of rock or debris washed down by the stream and piled up where the valley side joins the valley floor. Ribbon Lake (6): It is a long and narrow lake in a valley carved by a glacier. Truncated Spur (7): It is a ridge formed from where a glacier cut sharply through the valley. Misfit Stream (8): A stream in the valley that is too small to have formed the valley on its own. Hanging Valley (9): It is where the valley floor is higher than the main valley s floor. U-shaped Valley (10): A valley cut by a glacier with steep sides and a relatively flat floor
Crevasses: A deep crack or fracture in a ice sheet or glacier. Sun Cups: Bowl-shaped depressions on the surface of a glacier that form from the uneven heating of the surface of the glacier of ice cap. Cryoconites: A powdery windblown dust made of a combination of small rock particles and other material which is deposited and builds up on snow. Ice Cave: A type of natural cave that contains significant amounts of perineal ice year round. Moulin: A circular opening in the ice that allows water to enter from the surface. Striations: Horizontal scratches or gouges cut into the bedrock by abrasion. Chatter Marks: Crescent-shaped marks left by the chipping of the bedrock through plucking. Nunataks: An isolated peak of rock projecting above the surface of the ice. Snake Coils: Essentially miniature tunnel valleys, they are a snake coil-like shaped that occur along some ablation lines. Melt Ponds: Pools of open water that form on (and sometimes under) sea ice in spring and summer. Tunnel Valleys: a large, long, U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets
Types of Glaciers Division A Study Guide Mountain/Alpine Glaciers: Also known as alpine glaciers, they exist and mountain ranges and generally move from high to low elevations. Cirque Glacier: It is a bowl shaped hollow filled with ice. Mountain Ice Cap: It is a mass of ice that covers less than 50,000 km 2. Piedmont Glacier: They are fans or lobes of ice that form where a valley glacier spreads out to the adjacent plain. Valley Glacier: They are rivers of ice that flow downstream. Ice Tongue: valley glaciers that protrude out into the ocean as they elongate. Continental Glaciers/Ice Sheets: They are vast ice sheets that spread over thousands of kilometers of continental crust (must be greater than 50,000km 2 ). Antarctic Peninsula: the northernmost part of the mainland antarctica West Antarctic Ice Sheet (Lesser Antarctica): a segment of the Antarctic ice sheet on the side of the Transantarctic Mountains East Antarctic Ice Sheet (Greater Antarctica): a segment of the Antarctic Ice Sheet on the east side and the largest ice sheet in the world Temperate Glaciers: They occur where atmospheric temperatures become warm enough for the glacial ice to be around its melting temperature throughout the year. Polar Glaciers: They occur in regions where atmospheric temperatures stay cold enough year round that the ice remains below melting temperature throughout the year. Tidewater Glaciers: Glaciers that flow out out into sea along the coast. Ice Shelves: Broad, flat sheets of ice from continental glaciers entering the sea. Ice Fields: A large area of interconnected glaciers (usually found in mountainous regions). Ice Streams: A region of an ice sheet that moves significantly faster than the surrounding ice. Rock Glaciers: Distinctive landforms consisting of something between angular rock debris frozen in interstitial ice and former true glaciers overlain by a layer of talus.
Formation/Maintenance of Glaciers Division A Study Guide Solar Variability A change in the amount of energy produced by the sun Solar Cycle: Duration of 11 years from minimum to minimum Maximum is with maximum sunspots, while minimum is the opposite Most notable difference in temperature and ozone in the stratosphere Discovered by Samuel Heinrich Schwabe in 1843 Counted by Wolf Index Magnetic Cycle: Sunspots occur at different latitudes during different parts of the cycle Sunspots are strongly magnetized The magnetic polarity of sunspot pairs is: o Constant in a cycle o Opposite across the equator in a cycle o Reversed from one cycle to the next Since the cycle reveses, it takes 22 years for it to return to its original state The sun s magnetic field is generated by the solar dynamo Studied by George Hale Sunspots: Dark spots on the surface of the sun Regions of reduced surface temperature that emit more heat Caused by concentrations of magnetic field flux which create convection The closer they are to the equator, the closer it is to a solar minimum First appear at mid-latitudes Move towards the equator until a solar minimum occurs (then the cycle reverses)
Maunder Minimum: A time of very few sunspots that spanned from 1645 to 1715 Coincided with the middle of the little ice age that occured in Europe and North America Previously thought to have caused the little ice age (new research shows that there was also an increase in volcanic activity at the time) Named after Edward Walter Maunder after he extensively studied the event Insolation Amount of the sun s energy that strikes Earth s surface Milankovitch Cycle: The collective effects of the changes in the Earth s movement on its climate over thousands of years o Based on the following changes: Eccentricity: Earth s orbital path around the sun o 1,000 year cycle from one orbit to another and back again Obliquity: Variation in the tilt of Earth s axis over a 41,000 year cycle o Moves from 22 to 25 degrees o 41,000 year cycle from one tilt to another and back again Precession: Wobble of Earth s axis o 19,000 to 26,000 year cycle Dust Particles from Earth s surface carried into the atmosphere o Includes wind-eroded dust, volcanic particles (dust and gas), forest fires, etc Dust particles reflect incoming solar ultraviolet rays back to space, causing Earth s surface to cool
Greenhouse Gases Gases that absorb heat and raise the temperature of the atmosphere (can be natural and anthropogenic) Water vapor: the most abundant greenhouse gas; the warmer the atmosphere, the more vapor it can hold Carbon dioxide: released into the atmosphere through burning of wood and fossil fuels Methane: primary component of natural gas (used in houses for heat) Nitrous oxide: naturally present in the atmosphere through the nitrogen cycle Tropospheric Ozone: when pollutants break up the ozone layer, creating more tropospheric ozone CFCs: a harmful pollutant once used in refrigerators and aerosols Ocean Current Circulation The North Atlantic Deep Water Current is one long, continuous ocean current that takes about 1000 years to complete (The Great Conveyor) The warmer water from the equator rises, while the colder water from the poles sinks The more saline water sinks (it is more dense), while the less saline water rises o When glaciers melt, the water has a lower salinity, disrupting the current Sea Ice Ice that originates in the ocean from the ocean water freezes Reflects incoming solar radiation (albedo of about 95%) Blocks ocean water from sinking, thus preventing thermohaline circulation of ocean currents
Glacial Geology - Depositional Features Division A Study Guide Ice Rafted Debris: Rock material carried away by ice and meltwater Erratic: Rocks transported through glaciers actions placed into areas of differing rock types Kame Terraces: Debris deposited between glaciers and valley walls form conical, hilly deposits Till: Deposits formed underneath glaciers plastered down by moving ice as it drags debris across the land surface. Eskers: Superglacial material from the surface of a glacier carried through a moulin and into the glaciers plumbing system forming long snake-like (sinuous) ridges from the meltwater of a retreating glacier Drumlins: Material accumulates under a glacier, ix covered with till, and then reshaped into an elongated ridge; indicate the relative direction of the flow of the glaciers at the time they were formed Moraines: piles of rock material that have eroded from the valley walls and pushed to the front and sides of a glacier (see parts of a glacier) Glacial Flour (rock flour): Consists of fine-grained, silt-sized particles of rock; can accumulate in a lake, turning the water a turquoise-blue color Stratified: Heavier debris is dropped earlier than lighter debris, so the deposit is layered (stratified deposits are carried by water)