Rock Cycle
The Earth is active.
- Volcanoes are erupting and earthquakes are shaking;
- Mountains are being pushed up and are being worn down;
- Rivers are carrying sand and mud to the sea;
- Huge slabs of the Earth's surface called tectonic plates are slowly moving - about as fast as your fingernails grow.
Weathering and Erosion
Rocks of every sort and shape are worn away over time. Weathering is the process which breaks rocks into smaller bits. There are three main types:
- Physical weathering is a physical action which breaks up rocks : An example of this is called freeze-thaw weathering when water gets into tiny cracks in rocks. When the water freezes it expands, if this is repeated the crack grows and bits eventually break off.
- Chemical weathering is when the rock is chemically attacked: An example of this is the breakdown of limestone by acid rain.
- Biological weathering is when rocks are weakened and broken down by animals and plants. An example would be a tree root system slowly splitting rocks.
Erosion is a type of physical weathering which involves wearing down rocks.
There is an important point to remember. ROCKS ARE WEATHERED AT DIFFERENT RATES.
Granite is made up of large interlocking crystals (igneous rock) that give it a granular texture and make it one of the toughest rocks on Earth.
Sedimentary rocks such as sandstone tend to be much weaker.
Transportation
The rock cycle goes round and round, taking hundreds of millions of years. Once the rock has been broken down into smaller bits it's got to somehow move. Streams and rivers carry the small bits towards the sea (continually wearing down as the they progress). Big rivers such as the Ganga and the Bhramputra carry millions of tonnes of sediments out to sea each year.
|
Deposition Deposition simply means that the sand and sediments in the sea eventually settle to the bottom.LOOK AT THIS ANIMATION:- Sedimentary Rocks Sedimentary rocks are formed in three steps:
Sedimentary rock features
|
 |
Metamorphic Rocks
Heat and pressure make Metamorphic Rocks
Earth movements can push all types of rock deeper into the Earth. These rocks are then subjected to massive temperatures and pressures causing the crystalline structure and texture to change. THEY DO NOT MELT. The high pressure involved are often associated with mountain building processes.
Slate
This is formed from mudstone or clay and is the most common kind of metamorphic rock in Britain. Pressure causes new minerals to grow in parallel sheets - which makes slate split easily to make roofing tiles.
Marble
Marble is limestone that has been squashed and heated .The shells of the limestone breakdown and recrystallise into tiny crystals. Marble is chemically the same as limestone but it is much harder and far more expensive. Some of the finest marble comes from Italy and it is used for sculptures and as a fine building material.
Igneous Rocks
Igneous rocks form when molten rock (Magma if it is below the surface or lava if it has erupted from a volcano) solidifies. These rocks can be identified by the following tell-tale clues:
- Igneous rocks contain a minerals randomly arranged in
- If the rock has small crystals this means that it had rapidly cooled, possibly because it was erupted into the ocean. We call it an EXTRUSIVE IGNEOUS rock. If the rock has large crystals it means that it slowly cooled, the molten rock solidifies deep down within the crust without ever reaching the surface via an eruption. We call it an INTRUSIVE IGNEOUS rock.
- The rock are usually tough and hard (With the most famous exception being pumice stone).
This bit is worth remembering:
| BIG CRYSTALS | COOLED SLOWLY UNDERGROUND | INTRUSIVE |
| SMALL CRYSTALS | COOLED QUICKLY AFTER AN ERUPTION | EXTRUSIVE |
COMMON IGNEOUS ROCKS
Basalt
This is the most common form igneous rock which makes up most of the ocean floors. It is smooth and velvety-black in appearance and very hard. Basalt is formed when magma is erupted onto the sea-bed, as soon as it hits the cold sea water it cools quickly - it's got tiny crystals.
Pumice
This rock floats on water. Carbon dioxide and water dissolved in the molten rock is released with the decrease in pressure as it reaches the surface. Lava cools quite quickly in the air so the bubbles of gas get trapped.
Granite
If molten rock doesn't reach the surface via a volcano and cools underground instead, it solidifies very slowly (WHAT WOULD THE CRYSTAL SIZE BE?). This is because overlying layers of rock insulate the magma keeping it warm, this only allows gradual cooling. Some crystals grow to a much bigger size giving granite a speckled appearance. Granite is the most common form of igneous rock
- A volcano is generally a conical shaped hill or mountain built by accumulations of lava flows, tephra, and volcanic ash.
- About 95% of active volcanoes occur at the plate subduction zones and at the mid-oceanic ridges.
- The other 5% occur in areas associated with lithospherichot spots.
- These hot spots have no direct relationships with areas of crustal creation or subduction zones.
- It is believed that hot spots are caused by plumes of rising magma that have their origin within the asthenosphere.
- Most active volcanoes have a crater at the top. Materials which poured out from it usually include lava, steam, gaseous compounds of sulphur, ash and broken rock pieces.
- Volcanoes erupt when magma and pressure come together, and the pressure blasts the magma out of the top it shoots out what's left of the magma.
- Volcanoes are also found on planets other than Earth, like the Olympus Mons on Mars.
- Over the last 2 million years, volcanoes have been depositing lava, tephra, and ash in particular areas of the globe.
- These areas occur at hot spots, rift zones, and along plate boundaries where tectonic subduction is taking place.
Types of Volcanoes
Not all volcanoes are the same. Geologists have classified five different types of volcanoes. This classification is based on the geomorphic form, magma chemistry, and the explosiveness of the eruption.
The least explosive type of volcano is called a basalt plateau. These volcanoes produce a very fluid basaltic magma with horizontal flows. The form of these volcanoes is flat to gently sloping and they can occupy an area from 100,000 to 1,000,000 square kilometers. Deposits of these volcanoes can be as thick as 1800 meters. Large basalt plateaus are found in the Columbia River Plateau, western India, northern Australia, Iceland, Brazil, Argentina, and Antarctica.
Some basaltic magmas can produce very large slightly sloping volcanoes, 6 to 12°, that have gently flowing magmas called shield volcanoes Shield volcanoes can be up to 9000 meters tall. The volcanoes of the Hawaiian Islands are typical of this type. Extruded materials from this type of volcano mainly consist of low viscosity basaltic lava flows
A cinder cone is a small volcano, between 100 and 400 meters tall, made up of exploded rock blasted out of a central vent at a high velocity . These volcanoes develop from magma of basaltic to intermediate composition (andesite). They form when large amounts of gas accumulate within rising magma. Examples of cider cones include Little Lake Volcano in California and Paricuti Volcano in Mexico.
Composite volcanoes are made from alternate layers of lava flows and exploded rock. Their height ranges from 100 to 3500 meters tall. The chemistry of the magma of these volcanoes is quite variable ranging from basalt to granite. Magmas that are more granitic tend to be very explosive because of their relatively higher water content. Water at high temperatures and pressures is extremely volatile. Examples of composite volcanoes include Italy's Vesuvius, Japan's Mount Fuji, and Washington State's Mount Rainier and Mount St. Helens.
The most explosive type of volcano is the caldera. The cataclysmic explosion of these volcanoes leaves a huge circular depression at the Earth's surface. This depression is usually less than 40 kilometers in diameter. These volcanoes form when "wet" granitic magma quickly rises to the surface of the Earth. When it gets to within a few kilometers of the surface the top of the magma cools to form a dome. Beneath this dome the gaseous water in the magma creates extreme pressures because of expansion. When the pressure becomes too great the dome and magma are sent into the Earth's atmosphere in a tremendous explosion. On the island of Krakatau, a caldera type volcano exploded in 1883 ejecting 75 cubic kilometers of material in the air and left a depression in the ground some 7 kilometers in diameter.
A potentially very destructive caldera covering an area of about 2000 square kilometers exists under Yellowstone National Park in the United States. Investigations have discovered that over the last 2 million years this volcano has exploded on a regular interval of about 700,000 years. The last eruption occurred 630,000 years ago and the next could take place anytime.When the Yellowstone caldera last erupted, it blasted 1,000 cubic kilometers of volcanic ash and rock into the atmosphere. The ash ejected into the atmosphere created climatic havoc on a global scale. The ash would have blocked sunlight from being received at the ground surface for a few years. A reduction in the reception of solar radiation would have caused the globle climate to cool significantly. Over time this ash settled back to the Earth's surface covering more than half of North America.
Weathering is the breakdown and alteration of rocks and minerals at or near the Earth's surface into products that are more in equilibrium with the conditions found in this environment. Most rocks and minerals are formed deep within the Earth's crust where temperatures and pressures differ greatly from the surface. Because the physical and chemical nature of materials formed in the Earth's interior are characteristically in disequilibrium with conditions occurring on the surface. Because of this disequilbrium, these materials are easily attacked, decomposed, and eroded by various chemical and physical surface processes.
Weathering is the first step for a number of other geomorphic and biogeochemical processes. The products of weathering are a major source of sediments for erosion and deposition. Many types of sedimentary rocks are composed of particles that have been weathered, eroded, transported, and terminally deposited in basins. Weathering also contributes to the formation of soil by providing mineral particles like sand, silt, and clay. Elements and compounds extracted from the rocks and minerals by weathering processes supply nutrients for plant uptake. The fact that the oceans are saline in the result of the release of ion salts from rock and minerals on the continents. Leaching and runoff transport these ions from land to the ocean basins where they accumulate in seawater. In conclusion, weathering is a process that is fundamental to many other aspects of the hydrosphere, lithosphere, and biosphere.
There are three broad categories of mechanisms for weathering:
- Chemical
- Physical
- Biological
Products of Weathering
The process of weathering can result in the following three outcomes on rocks and minerals:
(1). The complete loss of particular atoms or compounds from the weathered surface.
(2). The addition of specific atoms or compounds to the weathered surface.
(3). A breakdown of one mass into two or more masses, with no chemical change in the mineral or rock.
The residue of weathering consists of chemically altered and unaltered materials. The most common unaltered residue is quartz. Many of the chemically altered products of weathering become very simple small compounds or nutrient ions. These residues can then be dissolved or transported by water, released to the atmosphere as a gas, or taken up by plants for nutrition. Some of the products of weathering, less resistant alumino-silicate minerals, become clay particles. Other altered materials are reconstituted by sedimentary or metamorphic processes to become new rocks and minerals.
Chemical Weathering
Chemical weathering involves the alteration of the chemical and mineralogical composition of the weathered material. A number of different processes can result in chemical weathering. The most common chemical weathering processes are hydrolysis, oxidation, reduction, hydration, carbonation, and solution.
Hydrolysis is the weathering reaction that occurs when the two surfaces of water and compound meet. It involves the reaction between mineral ions and the ions of water (OH- and H+), and results in the decomposition of the rock surface by forming new compounds, and by increasing the pH of the solution involved through the release of the hydroxide ions. Hydrolysis is especially effective in the weathering of common silicate and alumino-silicate minerals because of their electrically charged crystal surfaces.
Oxidation is the reaction that occurs between compounds and oxygen. The net result of this reaction is the removal of one or more electrons from a compound, which causes the structure to be less rigid and increasingly unstable. The most common oxides are those of iron and aluminum, and their respective red and yellow staining of soils is quite common in tropical regions which have high temperatures and precipitation. Reduction is simply the reverse of oxidation, and is thus caused by the addition of one or more electrons producing a more stable compound.
Hydration involves the rigid attachment of H+ and OH- ions to a reacted compound. In many situations the H and OH ions become a structural part of the crystal lattice of the mineral. Hydration also allows for the acceleration of other decompositional reactions by expanding the crystal lattice offering more surface area for reaction.
Carbonation is the reaction of carbonate and bicarbonate ions with minerals. The formation of carbonates usually takes place as a result of other chemical processes. Carbonation is especially active where the reaction environment is abundant with carbon dioxide. The formation of carbonic acid, a product of carbon dioxide and water, is important in the solution of carbonates and the decomposition of mineral surfaces because of its acidic nature.
Water and the ions it carries as it moves through and around rocks and minerals can further the weathering process. Geomorphologists call this phenomena solution. The effects of dissolved carbon dioxide and hydrogen ions in water have already been mentioned, but solution also entails the effects of a number of other dissolved compounds on a mineral or rock surface. Molecules can mix in solution to form a great variety of basic and acidic decompositional compounds. The extent, however, of rock being subjected to solution is determined primarily by climatic conditions. Solution tends to be most effective in areas that have humid and hot climates.
The most important factor affecting all of the above mentioned chemical weathering processes is climate. Climatic conditions control the rate of weathering that takes place by regulating the catalysts of moisture and temperature. Experimentation has discovered that tropical weathering rates, where temperature and moisture are at their maximum, are three and a half times higher than rates in temperate environments.
Physical Weathering
Physical weathering is the breakdown of mineral or rock material by entirely mechanical methods brought about by a variety of causes. Some of the forces originate within the rock or mineral, while others are applied externally. Both of these stresses lead to strain and the rupture of the rock. The processes that may cause mechanical rupture are abrasion, crystallization, thermal insolation, wetting and drying, and pressure release.
Abrasion occurs when some force causes two rock surfaces to come together causing mechanical wearing or grinding of their surfaces. Collision between rock surfaces normally occurs through the erosional transport of material by wind, water, or ice.
Crystallization can cause the necessary stresses needed for the mechanical rupturing of rocks and minerals. Crystal growth causes stress as a result of a compound's or an element's change of physical state with change in temperature. The transformation from liquid to solid crystalline form produces a volumetric change which in turn causes the necessary mechanical action for rupture. There are primarily two types of crystal growth that occur; they are ice and salt. Upon freezing the volumetric change of water from liquid to solid is 9%. This relatively large volumetric change upon freezing has potentially a great rupturing effect. Several researchers have discovered in the laboratory and the field that frost action plays a major role in weathering in temperate and polar regions of the Earth. The threshold temperature for frost action is at least - 5° Celsius, and it is at this temperature that the most effective rupturing occurs.
The crystallization of salt exhibits volumetric changes from 1 to 5 percent depending on the temperature of the rock or mineral surface. Most salt weathering occurs in hot arid regions, but it may also occur in cold climates. For example, cavernous salt weathering of granite is widespread in the dry valley regions of South Victoria Land, Antarctica. At this location outcrops and large boulders are pitted by holes up to 2 meters in diameter. Researchers have also found that frost weathering is greatly enhanced by the presence of salt.
The physical breakdown of rock by their expansion and contraction due to diurnal temperature changes is one of the most keenly debated topics in rock weathering research. Known as insolation weathering, it is the result of the physical inability of rocks to conduct heat well. This inability to conduct heat results in differential rates of expansion and contraction. Thus, the surface of the rock expands more than its interior, and this stress will eventually cause the rock to rupture. Differential expansion and contraction may also be due to the variance in the colors of mineral grains in rock. Dark colored grains, because of their absorptive properties, will expand much more than light colored grains. Therefore, in a rock peppered with many different colored grains, rupturing can occur at different rates at the various mineral boundaries.
wetting and drying of rocks, sometimes known as slaking, can be a very important factor in weathering. Slaking occurs by the mechanism of "ordered water", which is the accumulation of successive layers of water molecules in between the mineral grains of a rock. The increasing thickness of the water pulls the rock grains apart with great tensional stress. Recent research has shown that slaking in combination with dissolved sodium sulfate can disintegrate samples of rock in only twenty cycles of wetting and drying.
Pressure release of rock can cause physical weathering due to unloading. The majority of igneous rocks were created deep under the Earth's surface at much higher pressures and temperatures. As erosion brings these rock formations to the surface, they become subjected to less and less pressure. This unloading of pressure causes the rocks to fracture horizontally with an increasing number of fractures as the rock approaches the Earth's surface. Spalling, the vertical development of fractures, occurs because of the bending stresses of unloaded sheets across a three dimensional plane.
Biological Weathering
Biological weathering involves the disintegration of rock and mineral due to the chemical and/or physical agents of an organism. The types of organisms that can cause weathering range from bacteria to plants to animals.
Biological weathering involves processes that can be either chemical or physical in character. Some of the more important processes are:
1. Simple breaking of particles, by the consumption of soils particles by animals. Particles can also fracture because of animal burrowing or by the pressure put forth by growing roots.
2. Movement and mixing of materials. Many large soil organisms cause the movement of soil particles. This movement can introduce the materials to different weathering processes found at distinct locations in the soil profile.
3. Simple chemical processes like solution can be enhanced by the carbon dioxide produced by respiration. Carbon dioxide mixing with water forms carbonic acid.
4. The complex chemical effects that occur as a result of chelation. Chelation is a biological process where organisms produce organic substances, known as chelates, that have the ability to decompose minerals and rocks by the removal of metallic cations.
5. Organisms can influence the moisture regime in soils and therefore enhance weathering. Shade from aerial leaves and stems, the presence of roots masses, and humus all act to increase the availability of water in the soil profile. Water is a necessary component in several physical and chemical weathering processes.
6. Organisms can influence the pH of the soil solution. Respiration from plant roots releases carbon dioxide. If the carbon dioxide mixes with water carbonic acid is formed which lowers soil pH. Cation exchange reactions by which plants absorb nutrients from the soil can also cause pH changes. The absorption processes often involves the exchange of basic cations for hydrogen ions. Generally, the higher the concentration of hydrogen ions the more acidic a soil becomes.
Factors that Influence Weathering
-
Rock Type and Structure:
-
Different rocks are composed of different minerals, and each mineral has a different susceptibility to weathering. For example a sandstone consisting only of quartz is already composed of a mineral that is very stable on the Earth's surface, and will not weather at all in comparison to limestone, composed entirely of calcite, which will eventually dissolve completely in a wet climate.
-
Bedding planes, joints, and fractures, all provide pathways for the entry of water. A rock with lots of these features will weather more rapidly than a massive rock containing no bedding planes, joints, or fractures.
-
- If there are large contrasts in the susceptibility to weathering within a large body of rock, the more susceptible parts of the rock will weather faster than the more resistant portions of the rock. This will result in differential weathering.
- Slope - On steep slopes weathering products may be quickly washed away by rains. On gentle slopes the weathering products accumulate. On gentle slopes water may stay in contact with rock for longer periods of time, and thus result in higher weathering rates.
- Climate- High amounts of water and higher temperatures generally cause chemical reactions to run faster. Thus warm humid climates generally have more highly weathered rock, and rates of weathering are higher than in cold dry climates. Example: limestones in a dry desert climate are very resistant to weathering, but limestones in a tropical climate weather very rapidly.
- Animals- burrowing organisms like rodents, earthworms, & ants, bring material to the surface were it can be exposed to the agents of weathering.
- Time - since a rate is how fast something occurs in a given amount of time, time is a crucial factor in weathering. Depending on the factors above, rates of weathering can vary between rapid and extremely slow, thus the time it takes for weathering to occur and the volume of rock affected in a given time will depend on slope, climate, and animals.
Fold Mountains
Fold mountains are created by uplift and folding of tectonic plates as they move towards each other and collide. This is known as a compressional plate margin. An example is the Andes Mountain range in South America Nazca Plate colliding with the South American Plate
The plates may be either 'continental and continental' or 'continental and oceanic'. The plates move towards each other, but there isn't a free space for them to move into because they are already touching each other. With two massive plates of rock pushing against each other and continually moving, all that rock has to go somewhere!
At a destructive plate margin where oceanic and continental plates collide, the oceanic plate is subducted, pulled under the continental plate - whilst the continental plate is crumpled upwards to form a mountain range. The Andes are an example of fold mountains formed at a destructive plate margin.
When two continental plates move towards each other, both plates are forced upwards in a series of folds. This caused big problems for early geologists who struggled to explain why they were finding fossils of sea creatures high up in mountains such as the Himalayas! We now know that the fossils got there due to uplift of sedimentary rocks found along the edges of the plates. Previous suggestions often centered on religious myths / beliefs such as Noah's Great Flood.
You can simulate this process using two flat strips of modeling clay or old carpet. Put them side by side and push them together. One or both will crumple up and form a mini mountain range on your table top.
Human Activity in Fold Mountains
The European Alps are a popular tourist location, as well as home to over eleven million people. Countries such as France,Italy,Switzerland,Austria and Germany have developed tourism in their mountains and have thriving tourism sectors. Not all fold mountain areas as as well developed as the Alps of course. The Himalayas are popular with tourists, but much harder for Europeans, Africans and Americans to get to. Whilst the European Alps are the most populated mountains in the world, the Himalayas have a low population density and are so high that people cannot survive for long in the highest parts!
In the Alps the economy is based on forestry (coniferous trees on steep slopes), keeping dairy cattle and sheep (valley floors, and high pasture in summer), herding goats in the highest areas, and meeting the needs of tourists throughout the summer and winter.
The Alps have hot, dry summers and cold, snowy winters, so the tourism industry has two profitable seasons; Summer and Winter.
During the summer (June to September) the area fills with tourists from across Europe, staying in hotels, camping sites and rented homes. Typical summer activities include walking, climbing, enjoying the clean air and beautiful views, hang gliding and other adventure activities.
Winter brings skiing, winter climbing, snow boarding and people wanting a 'traditional' Christmas with snow, sleighs and fir trees. Many winter resorts have been built specifically for tourism, such as Les Deux Alps and Val d'Isere, whilst others have adapted over time, such as Chamonix, Val Ferret and Grindelwald. Most winter resorts have a well developed summer tourist industry too.
Power Generation in Fold Mountains
HEP took of after the Second World War when it became possible to transmit the power over long distances and produce more and more power from better power plants. Today, almost two thirds of Switzerland's electricity comes from HEP. Hydro-electric power has important ecological advantages because it doesn't produce air pollution, greenhouse gases or waste products. It is renewable too, so once the plant is built you don't have 'raw materials' costs as you do with coal or oil powered generation.
On the other hand, to ensure a constant water supply for a modern HEP plant, it is necessary to create reservoirs. Local people can sometimes object to this, especially if their homes are in a valley due to be flooded to create a new reservoir. Additionally, because the rivers are now controlled and flow into reservoirs before they reach the lowland valleys, their ecosystems have changed. Rivers that used to be fast flowing have less water in them, and are more likely to become polluted. To protect them, governments set minimum discharge rates through the HEP dams to ensure that the rivers keep flowing. The people running the HEP plants don't always like this because water that is discharged without going through the turbines doesn't produce electricity or profits. It's a delicate balancing act between the needs of power users and the needs of the ecosystem and other river users.
Landform
A landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography.
Landform elements also include seascape and oceanic waterbody interface features such as bays, peninsulas, seas and so forth, including sub-aqueous terrain features such as submersed mountain ranges, volcanoes, and the great ocean basins.
Aeolian landform
Aeolian landforms are features of the Earth's surface produced by either the erosive or constructive action of the wind.
- This process is not unique to earth, and it has been observed and studied on other planets, including Mars.
- In aeolian processes, wind transports and deposits particles of sediment.
- Aeolian features form in areas where wind is the primary source of erosion.
- The particles deposited are of sand, silt and clay size.
- The particles are entrained in by one of four processes.
- Creep occurs when a particle rolls or slides across the surface.
- Lift occurs when a particle rises off the surface due to the Bernoulli effect.
- If the airflow is turbulent, larger particles are transported by a process known as saltation.
- Finally, impact transport occurs which one particle strikes another causing the second particle to move.
Fluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used.
Fluvial processes comprise the motion of sediment and erosion or deposition (geology) on the river bed.
Erosion by moving water can happen in two ways. Firstly, the movement of water across the bed exerts a shear stress directly onto the bed. If the cohesive strength of the substrate is lower than the shear exerted, or the bed is composed of loose sediment which can be mobilized by such stresses, then the bed will be lowered purely by clearwater flow. However, if the river carries significant quantities of sediment, this material can act as tools to enhance wear of the bed (abrasion). At the same time the fragments themselves are ground down, becoming smaller and more rounded (attrition).
Sediment in rivers is transported as either bedload (the coarser fragments which move close to the bed) or suspended load (finer fragments carried in the water). There is also a component carried as dissolved material.
For each grain size there is a specific velocity at which the grains start to move, called entrainment velocity. However the grains will continue to be transported even if the velocity falls below the entrainment velocity due to the reduced (or removed) friction between the grains and the river bed. Eventually the velocity will fall low enough for the grains to be deposited. This is shown by the Hjulstrøm curve.
A river is continually picking up and dropping solid particles of rock and soil from its bed throughout its length. Where the river flow is fast, more particles are picked up than dropped. Where the river flow is slow, more particles are dropped than picked up. Areas where more particles are dropped are called alluvial or flood plains, and the dropped particles are called alluvium.
Glacial landforms
Glacial landforms are those created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations.
As the glaciers expanded, due to their accumulating weight of snow and ice , they crushed and scoured surface rocks and bedrock. The resulting erosional landforms include striations, cirques, glacial horns, arêtes, trim lines, U-shaped valleys, roches moutonnées, overdeepenings and hanging valleys.
