Geology 20 (Glaciers and Ice Sheets)

Earth and Space Sciences X

29 Oct 201557:07

EducationalLearning

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TLDRThe video explores how glaciers form over hundreds of thousands of years from compacted snow that crystallizes into solid ice. It details how glaciers erode the land, transport sediment, and leave behind distinct landforms. The script discusses glacial cycles during ice ages as well as the possible causes of historical climate shifts from small orbital changes to today's human-induced factors. Overall, a compelling overview of how glaciers impact topography over time through erosion and deposition.

Takeaways

😄 Glaciers behave like metamorphic rocks, flowing under pressure and recrystallizing from snow into firm and glacial ice.
❄ Glaciers can erode underlying bedrock and transport huge amounts of sediment long distances through processes like plucking and abrasion.
🏔 Glaciers create distinctive landforms like U-shaped valleys, hanging valleys, aretes, horns, moraines, and erratics.
🌊 Glaciers influence and are influenced by sea levels over time through ice sheet advances and retreats.
🔎 Scientists study glacial deposits and moraines to infer ancient climate patterns and conditions like ice ages.
🌡 Earth's climate fluctuates naturally between glacial and interglacial periods over thousands-millions of years.
🌀 Changes in earth's orbit and axis angle/orientation contribute to cycles between cold glacial and warmer interglacial periods.
⛄ Glaciers currently only exist in cold, high-altitude and high-latitude regions where more snow falls than melts annually.
🚧 Glaciers can burst in sudden fast-moving surges, or dam huge meltwater lakes that breach violently like Lake Missoula.
🔥 Today's rapid climate warming and glacial melting likely relates more to modern human GHG emissions than natural cycles.

Q & A

What are the two main types of glaciers?
-The two main types of glaciers are valley glaciers and ice sheets. Valley glaciers exist in mountain valleys while ice sheets are larger and cover entire regions.
How does a glacier move?
-A glacier moves through a combination of basal sliding along the ground and internal deformation, where the ice flows like a viscous fluid. The bottom slides along the bedrock while the top moves faster due to the internal flow.
What landforms are created by glaciers?
-Glaciers create distinctive landforms like U-shaped valleys, hanging valleys, arêtes, horns, drumlins, moraines, outwash plains, kettles, and fjords.
What is plucking?
-Plucking is the process where blocks of bedrock are pulled loose and transported by glacial ice. The ice freezes onto and lifts the rocks as the glacier moves.
How does a glacier erode the underlying bedrock?
-Glaciers erode bedrock through abrasion and plucking. Rocks embedded in the ice grind and smooth the underlying surface like sandpaper. The ice also plucks and transports blocks of bedrock.
What are ice shelves?
-Ice shelves are the floating extensions of ice sheets that extend into the ocean. They can be grounded if shallow or float freely in deeper waters, and sometimes break off to form icebergs.
What is the evidence for past glaciations?
-The evidence for past glaciations includes features like moraines, drumlins, striations, hanging valleys, glacial erratics, and deposits like till which reveal that ice once covered areas.
What causes ice ages?
-There is no definitive explanation, but factors like changes in Earth's orbit, shifts in solar radiation, atmospheric changes, and plate tectonics may contribute to ice ages over time.
What ended the last ice age?
-The last ice age ended about 11,700 years ago. Increasing northern summer sunlight along with higher CO2 levels and warming oceans are believed to have caused the glaciers to retreat.
How do glaciers affect sea level?
-Glaciers tie up water on land in the form of ice. When they grow, such as in an ice age, they lower sea levels globally. When the ice melts during warmer interglacials, the water is released back into the oceans, causing sea level rise.

Outlines

00:00

😀 Introducing Glaciers

The first paragraph introduces glaciers, describing them as thick masses of ice that form over hundreds of thousands of years from compacted snow. It explains that glacial ice is a mineral with a crystal structure, allowing it to flow like a fluid. The paragraph also introduces the concepts of glacial zones of accumulation and wastage.

05:02

🌨️ Modern and Ancient Ice Sheets

The second paragraph discusses modern and ancient ice sheets in Greenland, Antarctica, Siberia, and Europe. It explains how ice sheets have advanced and retreated multiple times over the past 2.6 million years.

10:03

❄️ Glacier Structure and Movement

The third paragraph examines glacier structure and movement. It describes zones of fracture and plastic flow, crevasses, glacial velocity and surges, the role of basal slip, and features such as ice shelves and calving.

15:04

☃️ Glacial Ice Formation

The fourth paragraph outlines the process of glacial ice formation from compacted snow, explaining how air gets forced out and snow crystals fuse into interlocking ice crystals under pressure.

20:06

🥶 Internal Glacier Flow

The fifth paragraph contrasts internal glacier flow and basal sliding, discussing shear and how the brittle upper zone of a glacier fractures while plastic flow seals cracks at depth.

25:08

🗻 Alpine Glacier Erosion

The sixth paragraph examines alpine glacier erosion, describing how they shape mountain peaks and valleys, creating features like u-shaped troughs, hanging valleys, arêtes, and horns.

30:10

🏔️ Glacial Transport and Deposition

The seventh paragraph discusses glacial transport and deposition, covering processes like plucking and abrasion as well as landforms like moraines, drumlins, fjords, and outwash plains.

35:11

🧊 Glacial Till and Drift Deposits

The eighth paragraph differentiates between unstratified glacial till and sorted, layered glacial drift deposits, describing features like erratics, lateral moraines, outwash plains, kettles, and drumlins.

40:13

🌬️ Glacial Effects on Landscape

The ninth paragraph examines wider glacial effects on landscape, discussing drowned glacial troughs that created fjords, as well as isostatic rebound causing earthquakes and sea level changes from loading/unloading of ice.

45:13

💧 Catastrophic Glacial Outburst Floods

The tenth paragraph looks at catastrophic flooding events caused by failure of ice dams, using the huge Missoula Floods as an example case and examining the immense scale of the ripple marks left behind.

50:14

🌡️ Cycles of Glaciations and Interglaciations

The eleventh paragraph introduces cycles of glaciations and interglaciations, examining onset and alterations between these stages over the past 3 million years in the Northern Hemisphere and 30 million years in the Antarctic.

55:17

🔁 Orbital Influences on Glacial Cycles

The final paragraph suggests influences on glacial cycles like elliptical orbits, shifts in axial tilt, and precessional wobbles, which may act as triggers between glacial and interglacial periods.

Mindmap

Keywords

💡glacier

A glacier is a thick mass of ice that forms over hundreds of thousands of years by the accumulation, compaction and recrystallization of snow. Glaciers behave like viscous fluids and are able to flow like rivers. The video focuses on the formation, movement and geological impacts of glaciers.

💡ablation

Ablation refers to the loss of ice from a glacier, usually through melting at the terminus. If ablation exceeds accumulation at the formation zone, the glacier will retreat. Understanding ablation is key to analyzing glacial budgets and advance/retreat cycles.

💡moraine

A moraine is a landform composed of unsorted glacial sediments (till) that are directly deposited by glacier ice. The video describes lateral, medial, ground and terminal moraines created by alpine glaciers.

💡drumlin

Drumlins are smooth, elongated hills composed of till that are molded under moving ice sheets. They indicate the direction of past ice flow.

💡ice age

An ice age refers to a long interval of time when ice sheets and glaciers expand across earth's surface. The video explains how ice ages are normal earth cycles spanning millions of years.

💡interglacial

An interglacial period is a warmer interval between colder glacial periods. The video describes the cyclical alternation between glacial and interglacial stages.

💡sea level

Glacial advance and retreat significantly affects global sea levels. At the last glacial maximum 18,000 years ago, sea level was 330 feet/100 m lower due to water being locked in ice sheets.

💡orbit

Variations in the ellipticity, angle and wobble of Earth's orbit are closely tied to climate fluctuations between glacial and interglacial periods over 100,000 year cycles.

💡plate tectonics

Continental drift changes ocean currents over millions of years. This gradual climate change is too slow to explain recent warming, implying other factors like human activity.

💡solar fluctuations

Changes in solar intensity are a potential trigger for ice ages and interglacials. The video cites this as a long-term factor unrelated to recent climate shifts.

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Transcripts

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