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/cm3 Firn: It is snow that persists for an entire year and has a density of about 0.6 g/cm3 Glacial Ice: It forms at a depth of about 50 meters deep and has a density of about 0.9 g/cm3 • 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 km2. 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 50,000km2). • 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.