Dynamic Planet: Glaciers

Dynamic Planet/Glaciers

• Glaciers is the topic of Dynamic Planet for the 2025 season
• The Dynamic Planet event was previously glaciers in 2013, 2014, and 2019

GMOA Notes

• The GMOA Notes are unsuitable for the Dynamic Planet topic

What are Glaciers

• Glaciers form from large masses of snow and ice accumulated over years
• Glacier thickness can range from a few dozen meters to over 2 kilometers
• Glaciers originate on land and can flow into the sea
• Glacier ice is formed from compression of snow and dense glacial ice
• Glaciers are immense bodies of ice, in gigaton mass, leaving behind unique landforms

Hubbard Glacier

• Hubbard Glacier is a tidewater valley glacier in Alaska and Canada
• It is the largest glacier in North America
• Hubbard Glacier has created and released many glacial lakes, creating floods
• This includes the second-largest glacial lake outburst flood (GLOF) ever recorded
• It routinely breaks off giant chunks of ice into Disenchantment Bay

Lambert Glacier

• Lambert Glacier is an outlet glacier on Antarctica
• Lambert Glacier is the largest glacier in the world, excluding ice fields, ice caps, and ice sheets
• It drains around 8% of the Antarctic Ice Sheet

Siachen Glacier

• The Siachen Glacier is a valley glacier in the eastern Karakoram range between India and Pakistan
• It is part of the ongoing Indian-Pakistani conflict in Kashmir
• At 76 kilometers long, it is the second-longest non-polar glacier in the world
• The Himalayan region is sometimes called the "Third Pole" due to extreme temperatures

Vatnajokull Glacier

• Vatnajokull is an ice cap in Iceland
• It is the largest glacier in Iceland, covering more than 9% of Iceland's land area
• This is the second-largest glacier by area in Europe
• It is known for its jökulhlaups, or glacial outburst floods, triggered by the volcanic activity of the island

Larsen B Glacier

• Larsen B was an ice shelf attached to the Antarctic Peninsula
• Approximately 3,250 square kilometers of Larsen B's floating ice broke off from the continent in 2002
• The rest disappeared and was stable for thousands of years
• Warm water currents were eating away at the underside of the shelf leading up to its collapse
• Smaller chunks being calved off occurred notably in 1998
• Ponds of meltwater formed during the 24-hour exposure to the sun during the Antarctic summer further caused collapse in 2002
• The light-blue mix in those frames is a mélange of slush and icebergs

Patagonian Ice Fields

• The North and South Patagonian Ice Fields are technically separate ice fields
• They are among the largest ice fields in the world
• They cover much of the Andes Mountains in Argentina and Chile
• The South Patagonian field is the larger of the two
• During the Last Glacial Period, the two fields were joined together as one
• They covered almost all of southern Chile and became an important site for climate change research

Greenland Ice Sheet

• The Greenland Ice Sheet covers about 80% of the surface of Greenland
• The Greenland Ice Sheet is second in size only to the Antarctic Ice Sheet
• With an average thickness of 2.1 km, a complete melt of the Greenland Ice Sheet would cause 7-8 meters of sea-level rise

Antarctic Ice Sheets

• The East and West Antarctic Ice Sheets comprise the vast majority of ice in Antarctica
• They also comprise the majority of ice in the world
• Both have dozens of outlet glaciers on their fringes
• Both are separated by the Transantarctic Mountains
• The East Antarctic Ice Sheet is significantly larger, having 9 times the volume of the West Antarctic Ice Sheet
• It contains about 4/5ths of all the world's ice
• The East Antarctic Ice Sheet is about 2.2 km thick on average, while the West is only 1.3 km thick
• Most of the West Antarctic Ice Sheet actually sits below sea level, which has left it more susceptible to melting and collapse
• Ice shelves that buttress it are also at risk
• West Antarctic Ice Sheet collapse would cause 6 meters rise in sea level
• A collapse of the East Antarctic Ice Sheet would cause a rise of over 55 meters

Laurentide Ice Sheet

• The Laurentide Ice Sheet was a historical ice sheet that covered most of North America during the Pleistocene glaciation
• It was 4-5 kilometers thick in many areas and perforated by many nunataks
• It left behind moraines, eskers, and till shaping modern North America
• The Great Lakes were deepened under the forces of the Laurentide Ice Sheet, reaching their present-day form
• It disappeared mostly at the end of the Pleistocene glaciation 11.7 Ka ago
• Left behind numerous large ice caps and glaciers in its former ranges, mostly in Canada

Glacier Formation

• Glaciers can form anywhere that the average annual temperature is low enough for snow to last all year round
• Typically these are located at high latitudes or high elevations
• Glaciers are found on approximately 15,000,000 square kilometers, around 10% of the world's land area in all seven continents
• Australia doesn't have glaciers, but New Zealand does

Néve and Firn

• First-year glacial snow is called névé which is partially melted & re-frozen, slightly compacted, and granular
• Note, névé is not a commonly recognized scientific term
• Accumulated snow that survived one melt season is known as firn
• Firn is denser and more re-frozen than névé and is very stiff

Glacier Composition

• Snow accumulates and lower, older snow begins to have its air bubbles squeezed out
• Once this ice lasts through summer months and achieves the critical mass that allows it to flow, it is considered a glacier
• When ice is formed under pressure, it is denser than "normal" ice due to lack of air bubbles
• The lack of air bubbles is also why glaciers and icebergs are bluish
• The difference in density between glacier ice and regular ice is only a few grams per cubic meter

Glacier Formation Factors

• A wide variety of conditions affect the formation and preservation of glaciers
• Some parameters have a much larger or smaller impact than others
• Precipitation, temperature, and insolation have the greatest impact

Preservation of Glaciers

• Debris cover can play a role
• Small amounts such as windblown dust and small rocks will absorb more heat
• Glaciers can become fully encased in debris
• The debris will create a protective shield, prevent sunlight from melting the glacier

Glacier Movement

• Glaciers move due to gravity
• Steeper inclines will lead to faster flow
• Glaciers generally cannot flow independently on level ground or over uphill terrain until they are over 60m thick
• Glaciers flow in three main ways
• Basal Sliding
• Internal Deformation
• Bed Deformation

Advance and Recession

• Adavance and recession of a glacier should not be confused wit hits flow
• A glacier never flows backward up the mountain, but it can have a net loss of ice at its terminus

Basal Sliding

• Occurs at the base of a glacier across the bedrock upon which it lies, typically with meltwater
• Thinner, steeper glaciers are most active
• Basal sliding is accomplished in three ways: Basal Slip, Enhanced Basal Creep, and Regelation Flow

Basal Slip

• Occurs when a thin layer of water between the ice and underlying rock lubricates the glacier for faster flow
• Meltwater can come from pressure-melting, percolation, and water channels such as moulins
• Basal slip is generally more applicable to smoother bedrock surface
• If enough meltwater is present, basal slip can allow for a surge to occur

Enhanced Basal Creep

• Takes place when the ice encounters a large obstacle
• The increase in pressure causes ice to deform plastically around the obstacle

Regelation Flow

• Happens when ice encounters a small bedrock obstacle
• The ice melts under the pressure and refreezes on the other side
• Only happens if the object is small enough to allow the latent heat on the lee side to be quickly be conducted to the stoss side

Internal Deformation

• Also known as Creep, Internal Flow, Plastic Flow, and Plastic Deformation
• Involves ice crystals slowly sliding across each other within the glacier
• Ice deforms because it behaves plastically with extreme pressures
• This is standard within glaciers
• Internal deformation occurs in all types of glaciers and is not reliant on meltwater

Variations in Internal Deformation

• Glaciers flow faster near their centers than their periphery due to internal deformation
• Ice can slide better against other ice than the rough, rocky bed
• Leads to the 'sagging' shape that can sometimes be seen in the ice

Bed Deformation

• Sometimes called Subglacial Deformation
• Involves the shifting of softer sediments to allow the glacier to move downhill
• Subglacial till is composed of unsorted sediments with a wide range of sizes
• Finer sediments deform readily when shear stress is applied and also have groundwater between particles
• Bed deformation depends on meltwater at the base
• Basal sliding is more efficient if water remains directly under surface of the ice
• Bed deformation is more prevalent where the sediment becomes saturated with water

Thermal Regime

• Meltwater is important in glacier flow
• The temperature of a glacier determines its thermal regime
• Thermal regime is generally considered another method of classifying glaciers

Cold-Based Glaciers

• Frozen effectively year-round, excluding seasonal melting near the surface
• Importantly, the base of the ice is frozen
• Generally found at higher latitudes and lower seasonal variations in temperatures
• Minimal to no meltwater and move exclusively via internal deformation
• The ice is generally frozen to the rock

Warm-Based Glaciers

• Also known as Wet-Based, known for meltwater
• They are close to their melting point during the year throughout the entire thickness of the glacier
• Generally found at lower latitudes
• Movement is largely through basal sliding
• Meltwater plays a substantial role, mainly coming from surface melt that is channeled to the bottom

Polythermal Glaciers

• Have components of both warm and cold temperatures
• Vary depending on the location
• Most valley glaciers are polythermal and contain elements of both warm locations depending on location

Other Factors Controlling Flow

• Bedrock conditions and terminal conditions play a major role in glacier movement
• Friction with rougher bedrock surfaces slows the motion of a glacier

Ice Shelf Buttressing

• Ice Shelf Buttressing occurs when an ice shelf prevents an outlet glacier from advancing
• Ice Shelf Buttressing is critical to the stability of Antarctic and Greenland ice sheets
• Tidewater glaciers, which empty into water without ice shelf-buttressing, generally have higher rates of flow and calving

Mass Balance

• Glacier's mass balance is the difference between accumulation and ablation
• Accumulation is the addition of snow or ice onto the glacier
• Ablation is the depletion of ice from the glacier
• Glaciers advance if there is net positive gain in ice
• Glaciers retreat when the opposite occurs
• Visual appearance of advance or retreat should not be confused with the flow of a glacier, which is always away from the glacier head

Zones and Sections

• Head: The upper/beginning only in mountain glaciers
• Foot/Terminus: The downhill end more in mountain/outlet glaciers; ice sheets will drain exclusively into outlet or terminate as ice shelf Ablation Zone: Area where annual melting is greater than accumulation always on lower "half" including terminus.
• Accumulation Zone: Where annual accumulation is greater than melting only on upper "half" becoming larger in winter
• Snow/Equilibrium/Firn Line: Line that divides the zones depending on time. On warmer months, up higher.

Moulins

• Are narrow, near-vertical tubes which start at the surface
• They are generally characteristic of mountain glaciers