How are glacial landforms developed? Flashcards
What is the process of oxidation in chemical weathering?
Some minerals in rocks react with oxygen, especially iron, becoming soluble under acidic conditions.
Oxidation damages iron-rich cements in sandstone.
What is carbonation in the context of weathering?
Rainwater combines with dissolved carbon dioxide to produce weak carbonic acid, which reacts with calcium carbonate in rocks.
This leads to the formation of calcium bicarbonate, which is soluble.
Define the term ‘solution’ in geological processes.
Any process by which a mineral dissolves in water, including specific processes like carbonation.
Some minerals dissolve only in very acidic water.
How do tree roots contribute to biological weathering?
Tree roots grow into cracks in rocks, exerting outward pressure and causing weathering.
They can also bring rock and soil to the surface when they topple.
What role do organic acids play in weathering?
Organic acids from decomposing plant and animal matter increase soil acidity and react with minerals in a process called chelation.
Blue-green algae can also produce weathering effects.
True or False: Carbonation is less effective in low temperatures.
False
Carbonation is more effective in cold water as carbon dioxide is more readily absorbed.
What is mass movement in geological terms?
The movement of slope material when gravitational forces exceed frictional forces.
This includes processes like rock fall and slides.
Describe the process of plucking in glacial erosion.
Meltwater seeps into rock joints, freezes, and pulls pieces of rock away as the glacier advances.
Plucking is also known as quarrying.
What is abrasion in the context of glacial processes?
Debris embedded in a glacier scours surface rocks as the glacier moves, wearing them away.
This process is similar to sandpapering.
List factors that influence rates of glacial abrasion.
- Presence of basal debris
- Debris size and shape
- Relative hardness of particles and bedrock
- Ice thickness
- Basal water pressure
- Sliding of basal ice
- Movement of debris to the base
- Removal of fine debris
Each factor affects the efficiency of abrasion differently.
What is nivation?
A glacial process that includes freeze-thaw action, solifluction, transport by running water, and possibly chemical weathering.
Nivation is responsible for the enlargement of hillside hollows.
What is the difference between till and outwash?
Till is deposited directly by ice, while outwash is deposited by meltwater.
Both are types of glacial deposits.
Fill in the blank: Glacial deposits are collectively known as _______.
[drift]
What are the two types of glacial till?
- Lodgement till
- Ablation till
Lodgement till is deposited by advancing ice, while ablation till is from melting ice.
What characterizes glacial till?
- Angular or sub-angular shape
- Unsorted
- Unstratified
These characteristics differentiate it from water-borne deposits.
Describe the formation of a corrie.
Corrie formation starts with nivation, leading to the accumulation of snow, which compresses into glacier ice and deepens the hollow through rotational movement and plucking.
Corries have a steep back wall and an over-deepened basin.
True or False: The length to height ratio of a corrie is usually between 2.8:1 and 3.2:1.
True
This ratio indicates the typical proportions of corries.
What is a rock lip?
A rock lip is a threshold feature in glacial landforms, marking the edge of a corrie or glacial hollow.
How is a corrie formed?
A corrie forms through glacial erosion, where ice deepens the hollow, leaving a higher lip as the front ice erodes less rapidly.
What can happen to a corrie in a post-glacial landscape?
It may become filled with water, forming a small circular lake or tarn.
What is an arete?
An arete is a narrow, steep-sided ridge found between two corries, often described as knife-edged.
What is the primary shape of a glacial trough?
Glacial troughs are usually U-shaped but can also be parabolic due to weathering and mass movement.
What is the role of glaciers in shaping valleys?
Glaciers erode the sides and floor of valleys, making them deeper, wider, and straighter.
What are roche moutonnees?
Roche moutonnees are projections of resistant rock in glacial troughs, shaped by pressure melting and abrasion.
What are ellipsoidal basins?
Ellipsoidal basins are major erosional landforms created by ice sheets, such as those formed by the Laurentide ice sheet.
What is a terminal moraine?
A terminal moraine is a ridge of till marking the maximum advance of a glacier, typically crescent-shaped.
What distinguishes a lateral moraine from a terminal moraine?
A lateral moraine runs along the edge of a glacial valley, while a terminal moraine is located at the glacier’s snout.
What is an erratic?
An erratic is a rock that differs in geology from the surrounding area, transported and deposited by glacial activity.
What is a drumlin?
A drumlin is a streamlined hill of glacial debris, often pear-shaped and aligned in the direction of ice flow.
Fill in the blank: A _______ is formed when a large mass of unstratified drift is deposited at the end of a period of ice sheet advance.
till sheet
What is lichenometry?
Lichenometry is a method of dating that uses the size of lichen colonies to estimate the age of rock surfaces.
What is the significance of isostatic lowering in glacial landscapes?
Isostatic lowering occurs due to the weight of ice sheets, altering the surface landscape.
What are recessional moraines?
Recessional moraines are ridges running parallel to the terminal moraine, formed during temporary pauses in glacier retreat.
What geological period contributed to the formation of the Snowdonia landscape?
The Snowdonia landscape formed between 500 and 400 million years ago during the Ordovician era.
True or False: Glacial landforms are interrelated and together make up characteristic landscapes.
TRUE
What happens to the ice cap at the end of the glacial period?
The ice cap melts, leading to the retreat of valley glaciers.
How do glaciers differ from rivers in terms of erosive power?
Glaciers have far more erosive power than the rivers that originally cut the valleys.
What is the Matterhorn an example of?
The Matterhorn is an example of a pyramidal peak formed by glacial erosion.
What is the typical elongation ratio for drumlins?
Typical elongation ratios for drumlins range from 2:1 to 7:1.
Describe the orientation of drumlins compared to roche moutonnees.
Drumlins are aligned in the direction of ice flow, while roche moutonnees indicate the direction of ice movement.
What is the Ffrancon glacial trough?
A U-shaped valley eroded by ice from the Ogwen valley, Llanberis Pass, and Glyder Mountains.
It is characterized by its formation through glacial activity.
What blocked the path of ice from the Ogwen valley?
An ice sheet that diverted the ice to the northwest.
This diversion affected the flow into the area now known as the Irish Sea.
What is a hanging valley?
A small former river valley occupied by less deep ice, resulting in less erosion compared to the main valley.
This leads to the formation of waterfalls where they meet the main valley.
What is a roche moutonnee?
A landform created by glacial erosion, featuring a smoothed up-glacier side and a steepened down-glacier side.
An example is found at Maes Caradoc.
Define aretes.
Narrow ridges formed between two cirques eroding back to back.
Examples include Crib-y-Ddysgl and Crib Goch in Snowdonia.
What is a terminal moraine?
A ridge of debris deposited at the end of a glacier.
Found on the western side of Nant Ffrancon, formed by the glacier from Cwm Gach.
What are drumlins?
Elongated hills formed by glacial deposition, typically 50-70 m high.
Found in the Conwy Valley, indicating the direction of glacial movement.
What are erratics?
Rocks that have been transported by glaciers and deposited in areas where they differ from the local geology.
Examples include rocks from Snowdonia found near Harlech.
What geomorphic processes modified the Snowdonia landscape after glacial retreat?
Permafrost processes, freeze-thaw cycles, and mass movement.
These processes led to features such as stone stripes and blockfields.
What is a blockfield?
A landscape covered with large boulders resulting from freeze-thaw weathering.
Commonly found on mountain summits and ridges in Snowdonia.
What created the increasingly parabolic shape of the Nant Ffrancon valley?
Mass movement processes leading to debris accumulation at the base of slopes.
This shape results from the ongoing erosion and deposition processes.
When was Snowdonia subjected to significant tectonic uplift?
During the period when the landscape was shaped by tectonic forces, leading to mountain formation.
Specific dates and events would require further research.
What is the Laurentide ice sheet?
A massive ice sheet that covered parts of North America during the Quaternary period.
It significantly influenced the landscape of Minnesota.
What geological features are found in Minnesota?
Volcanic and sedimentary rocks, granitic materials, and metamorphic gneiss.
These features are part of the Laurentian Shield.
How did the Laurentide ice sheet affect Minnesota’s landscape?
It eroded high mountains and created an ellipsoidal basin filled with thousands of lakes.
The erosion was particularly deep in the Arrowhead region due to weaker shale rocks.
What are lobes in the context of glaciation?
Tongues of ice that extend from a main ice sheet, responsible for transporting and depositing till.
In Minnesota, these lobes advanced and retreated multiple times.
What is the significance of the Quaternary period?
It encompasses the last 2 million years, characterized by glacial advances and retreats.
This period has been crucial for shaping many northern landscapes.
What are striations and what do they indicate?
Striations are grooves or scratches in rock that indicate the direction of ice advance.
They are formed by the abrasive action of moving glaciers.
How thick are many till deposits in the west of Minnesota?
More than 100 m thick.
Borehole drilling has shown till deposits in some areas to be as deep as 160 m without reaching bedrock.
What landscape features are found in the far southeast of Minnesota?
Steep hills and deep valleys.
This area was not extensively covered by the ice sheet.
What was the erosional impact of the Laurentide ice sheet?
Considerable, shaping the overall landscape of Minnesota.
Unlike alpine glaciation, it does not produce spectacular landforms.
What is characteristic of the till deposited by the Wadena Lobe?
Red and sandy, derived from red sandstone and shales.
It includes features like the Alexandria moraine and drumlin fields.
What is a proglacial lake and give an example?
A lake formed at the edge of a glacier, such as Lake Agassiz.
Lake Agassiz covered 440,000 km2 at its maximum.
What river drained from Lake Agassiz?
Glacial River Warren.
It flowed over a recessional moraine at Brown’s Valley.
What are the conditions of periglacial environments?
Permafrost, seasonal temperature variations, and freeze-thaw cycles.
These environments occur in high latitudes and continental interiors.
