Anatarctica is lake Vostok Ice movement and ice shelf formation • Continental ice moves by plastic flow from the thickest parts towards the thinner edges (Like pancake batter!) • Once the ice arrives at the edge of the water it forms the ice shelf The ice shelf becomes unstable and breaks apart forming icebergs If the glacier terminates at/near sea level at high latitudes the ice doesn’t melt at the front but it breaks into icebergs Calving= the breaking off of large pieces of ice (icebergs where the glacier has reached the sea) From chasing ice movie A giant iceberg, ~ 1.5 times the size of Greater Paris, broke off from the northern section of Antarctica’s Brunt Ice Shelf on 2/26/2021. New radar images, captured by the Copernicus Sentinel-1 mission, show the 1270 sq km iceberg breaking free and moving away rapidly from the floating ice shelf. Glaciologists have been closely monitoring the many cracks and chasms that have formed in the 150 m thick Brunt Ice Shelf over the past several years. Source ESA Type of glaciers: Valley (alpine) glaciers • Form on mountainous areas at high elevation • Flow down a valley from where it accumulates on the top of the mountains Movement of Alpine glaciers Alpine glaciers move under their own weight and downslope (work of gravity!) Like in a river, movement will be faster on the surface, slower at the bottom This causes the formation of fracture called crevasses Crevasses • Zone of fracture affects the uppermost 50 meters, where the ice behaves in a brittle, not plastic way – Tension causes crevasses to form • Highly pressured Ice can melt in places at the base of the glacier, producing rivers and lakes under the alpine glacier Lake under swiss glacier The glacier Terminus • Terminus is the front end of the glacier. • The ice reaches low elevation where the temperature is higher → melting ice washes off forming braided streams and lakes at the end of the glacier Ice caves at the terminus of the glacier Budget of a glacier • This applies to both continental and alpine glaciers • The budget of a glacier is the balance of mass between the accumulation (where the ice forms) and zone and the ablation zone (where melting of ice prevails) Zone of accumulation Zone of ablation The work of Ice: Glacial Erosion • • Plucking—lifting of rocks Abrasion Some of these large boulders are carried along with the ice and are left behind when the ice melts as erratic blocks The work of Ice: Glacial Erosion Abrasion is a form of erosion that creates grooves in the rocks at the bottom of the glacier (glacial striations), these show the direction of ice movement q glacial abrasion can also polish the rock rocks to a shine! Landforms by glacial erosion – Cirque – Horn – Arete – U-shaped valley – Hanging valley – Fjiord • Cirque bowl shaped depressions eroded by accumulating and moving glaciers • arrete (long ridges shaped by the moving glacier Hooker glacier, New Zealand small valley glaciers and cirques and ridges southeast of the terminus of Tonsina Glacier, north-central Chugach Mountains, Alaska, photo by Bruce Molnia, USGS HORN from glacial erosion of adjacent cirques The Matterhorn – Swiss Alps Hanging valley Formed when a smaller glacier “merged” into a larger one Yosemite NP U-shaped valley carved by glacier Darwin Canyon, Ca Fjord Glacial valley at sea level, is flooded by sea water and forms these long and deep navigable channels Unidentified locations in Norway from wikimedia Glacial lakes – from erosion • The scouring work of ice can generate depressions of the bottom of the glaciers. • Once the glacier is gone, these depressions will fill with water generating lakes that take names as “cirque lakes or Tarns if they form in the cirque, and pater noster lakes when there are several of them in sequence Tarn in the Carpatian Mountains Paternoster lakes form in a chain of glacially-dug bowls in front of the Lyell Glacier (Yosemite National Park, California) photo by NP service Till • Much like a stream of water, the glacier erodes rocks but also transports and deposits the eroded material • The material deposited by glacier is called Till • Poorly sorted, subrounded, and scratched! Products of glacial erosion: Glacial flour Pulverized rock fragments eroded by the grinding of rocks and transported by glaciers can remain as suspended load in lakes and rivers in mountain areas Peyton Lake, Banff, Alberta Depositional landforms: Moraines Moraines are accumulation of till to form ridges or layers Lateral moraine – till accumulates by the side of the valley Terminal/end moraine till accumulates at the terminus Medial moraine – till accumulates in the middle, at the convergence of two lateral moraines Ground moraine – till accumulates at the bottom of the glacier Examples of lateral and medial moraines Examples of Terminal moraine Terminal moraines mark the most advanced position of the glacier Two terminal moraines – sierra Nevada, convict lake Glacial lakes – from moraines • Glacial lakes form where the work of glacier created a basin that can hold water. • The Great Lakes are an example of glacial lakes formed by a combination of glacial processes with end moraines damming water Oceans The coastal zone The transitional zone between the ocean and the continental environments The coastal zone ✓ Types of coastal zone/coastlines ✓ Interactions between the sea and the coastline: erosion/transport/deposition ✓ Currents affecting the coastlines: longshore, rip, tides ✓ Coastal Hazards Emergent Coastlines • Steep Cliffs and marine terraces • Pacific Coastlines are mostly emergent • Relatively narrow beaches Submergent coastlines • Features of a submergent coast are: – Highly irregular shoreline – Estuaries – drown river mouths – Barrier Islands • Atlantic Coastlines are mostly submergent Chesapeake Bay is a submergent coastline Interaction of the sea with the coastlines • The coastline is shaped by the action of waves and longshore currents: • EROSION, TRANSPORT AND DEPOSITION Waves • Generated by the wind blowing onto the surface • Wave motion is influenced by water depth and shape of shoreline Wave erosion on emergent coastlines -> rocky shores/cliffs Breaking waves exert great force on the shore, generating typical erosional features fractures Waves erosional force Erosion is always more intense at headlands All type of coastlines experience higher level of erosion at headlands Because of the morphology of the sea bottom, waves arrive at a low angle with coastaline energy concentrates to sides and front of headlands ◼ Over time, wave erosion straightens any irregular shoreline Wave erosion on sandy shores • Waves break on the shore with significant mass and velocity → powerful erosion agents • The erosional power changes with the season La Jolla beach, Summer Winter Interaction between water and shore: longshore currents • Oblique waves produce longshore currents (surface currents) • In the surf zone, current flow parallel to the coast Which way is the longshore drift going? Rip Currents • Form where the coastline has a break in morphology that interefer with the longshore current • Rip current pull away from the shore longshore currents: water in motion erosion, transport and deposition Several landforms are created by the deposition of material carried by longshore currents • Barrier islands – bars • Tombolo • Spits • Sand/sediments are moved by the longshore currents • In time patterns of transport and deposition can significantly alter the coastline • example Barrier Islands Elongated, low ridges of sand (sand bars) that parallel the coast 3 to 30 kilometers offshore ◼ sand transported and deposited by longshore currents ◼ Landward of barrier island Marshes and wetlands can form Spits • Elongated ridges of sand • extends into the mouth of an adjacent bay • Often the end hooks landward modern barrier islands made of materials from moraines from earlier Glaciations The continental ice sheet advanced across Cape Cod to the islands about 23,000 years ago. Tombolo Greece Saunders, RI Tides • Periodic rise and fall of a body of water due to gravitational interactions between the Moon and Earth, and to a lesser degree, to the Sun. • The wavelength of an average tide can be up to 17,000 km (over 10,500 miles). Tides are caused by gravitational interaction Earth-Moon, the Sun plays a minor role Tidal currents Horizontal flow of water accompanying the rise and fall of the tide • Flood current advances into the coastal zone as the tide rises • Ebb currents- seaward movement of water as tide falls Their effect is especially evident through inlets Tidal flats • intertidal environments, found behind barrier islands and in bays • Mostly covered in water at high tide Currents and the coastal zone Surface currents are primarily driven by wind and Earth’s rotation, Surface currents have a climate-regulation effect on the coastal zone Global ocean surface currents: blue lines show cool currents; red lines show warm currents. Coastline Erosion hazard from storms Hurricane landing Hurricane strength: Saffir-Simpson scale Storm surge = coastal floods • raise average coastal water levels and can cause large damaging waves to reach land. • If the surge lands during high tide, the effect is significantly amplified. Coastline Erosion hazard: Longshore currents Tucker’s Island case study, New Jersey 1856 1928 1953 2005 In 1927, the lighthouse was destroyed when powerful longshore currents washed over 300 yards of the surrounding land out to sea. Building structures to prevent coastline erosion: 1-groins • • • • Built to maintain or widen beaches Constructed at a right angle to the beach to trap sand Updrift deposition Downdrift erosion • Groins Building structures to prevent coastline erosion: 2 – Jetties built in pairs to develop and maintain harbors Extend into the ocean at the entrances to rivers and harbors Breakwater • Offshore barrier parallel to the coast • Protects boats from the force of breaking waves Seawall • parallel to shore and close to the beach • Stops waves form reaching the beach areas behind the wall Other strategies to prevent coastline erosion: beach nourishment Miami Before and after Beach Nourishment • describes a process by which sand lost through erosion and longshore drift is replaced from sources outside of the eroding beach • Other strategies to avoid coastline erosion: relocation Cape Hatteras Light house 1893 Geology evidence of Climate Change • Climate is the product of Earth’s heat budget from the interactions between the Earth Systems – There are long and short term variables that affect climate • Evidence of climate change – Past glacial climate can be studied from landforms tills and moraine deposits Inter-glacial (warming periods) and life • Some interglacial periods were very warm and the sea-level rose much above the present level. • These fast fluctuations affect the development of coral reefs → getting smaller and smaller Bahamas Proxies of past climate: 1 – Ice core geochemistry • Collected from the polar ice caps Antarctica, Greenland or from alpine glaciers • Lower ice layers are older than the top layers – the core contains ice formed over thousand of years. • The inclusions or Atmospheric gases, especially greenhouse gases and volcanic ashes within the ice can then be used to reconstruct a climatic record over the age range of the core. Past climate proxies 2: oxygen stable isotopes • Fossils from limestone: CaCO3 calcite More O18= COLD & DRY → Glacial conditions. More O16 = WARM & WET → Interglacial conditions. Past climate proxies 3: pollen • Habitat and climate shifts in recent and historic past can be identified 

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