Unit 3 (Revision Guide) Flashcards
What is a tectonic plate and how do oceanic and continental plates differ?
Original: A tectonic plate is a rigid segment of the Earth’s lithosphere that moves over the asthenosphere. Oceanic plates are thinner (about 10–16 km), denser, and mainly composed of basalt, while continental plates are thicker (more than 33 km), less dense, and primarily made of granite.
Simple Terms: A tectonic plate is a large piece of the Earth’s crust that moves. Oceanic plates are thinner and heavier, made mostly of basalt. Continental plates are thicker and lighter, made mostly of granite.
What do the terms ‘island arc’ and ‘ocean trench’ refer to in plate tectonics?
Original: An island arc is a curved chain of volcanic islands that forms along a subduction zone where one oceanic plate descends beneath another. An ocean trench is a deep underwater depression formed at convergent boundaries where one tectonic plate is forced beneath another, such as the Mariana Trench.
Simple Terms: An island arc is a chain of volcanoes formed when one ocean plate goes under another. An ocean trench is a deep valley in the ocean floor where one plate slides under another.
What is sea floor spreading?
Original: Sea floor spreading is the process by which new oceanic crust is created at divergent (constructive) plate boundaries, such as the Mid-Atlantic Ridge, where magma rises from the mantle as tectonic plates move apart, solidifying to form new ocean floor.
Simple Terms: Sea floor spreading is when new ocean crust forms as plates move apart and magma rises to fill the gap, making the ocean floor wider.
What is a landform that can develop at a convergent plate boundary?
Original: Fold mountains can develop at convergent plate boundaries when two continental plates collide, causing the crust to crumple and fold upwards due to compression, as seen in the Himalayas.
Simple Terms: Fold mountains can form when two plates collide and push the land upward, like the Himalayas.
What features may be found at a divergent plate boundary?
Original: At divergent plate boundaries, features such as mid-ocean ridges, rift valleys, volcanic activity, and new oceanic crust formation can be found. These occur as tectonic plates move apart and magma rises to fill the gap, solidifying into new crust.
Simple Terms: At divergent boundaries, you can find mid-ocean ridges, new crust, rift valleys, and volcanoes where plates move apart.
How does plate tectonics help explain the development of mountains?
Original: The theory of plate tectonics explains mountain formation through the collision of tectonic plates at convergent boundaries. When continental plates collide, the crust is compressed and forced upward, forming fold mountains. When oceanic plates subduct beneath continental plates, volcanic mountains can form.
Simple Terms: Mountains form when plates collide and push the land up, or when magma rises at subduction zones to form volcanic mountains.
How does the theory of plate tectonics explain the formation of volcanoes, ocean trenches, and island arcs?
Original: Plate tectonics explains that volcanoes form at subduction zones, divergent boundaries, and hotspots due to magma rising to the surface. Ocean trenches form at convergent boundaries where one plate subducts beneath another. Island arcs develop at oceanic-oceanic convergent boundaries when the descending plate melts, creating magma that rises to form volcanic islands.
Simple Terms: Volcanoes form when magma rises at boundaries and hotspots. Ocean trenches form where plates slide under each other. Island arcs form when one ocean plate goes under another, causing magma to rise and create volcanic islands.
What is hydrolysis in the context of weathering?
Original: Hydrolysis is a chemical weathering process where water reacts with minerals, particularly feldspar in igneous and metamorphic rocks, transforming them into clay minerals like kaolinite. This process weakens the rock structure and promotes further breakdown.
Simple: Hydrolysis is when water reacts with minerals in rocks, turning them into clay, which makes the rocks weaker and easier to break.
What is carbonation in the context of weathering?
Original: Carbonation is a chemical weathering process in which carbon dioxide from the atmosphere dissolves in rainwater to form weak carbonic acid. This acid reacts with calcium carbonate in rocks like limestone, converting it into soluble calcium bicarbonate, which is easily washed away.
Simple: Carbonation is when rainwater mixes with carbon dioxide to form a weak acid that dissolves rocks like limestone, making them easier to break down.
Under what circumstances might freeze-thaw weathering occur?
Original: Freeze-thaw weathering occurs in environments with temperatures that fluctuate above and below freezing. During the day, water enters cracks in rocks, and at night, it freezes and expands by about 9%, widening the cracks. Repeated cycles cause the rock to fracture and break apart.
Simple: Freeze-thaw weathering happens where temperatures go above and below freezing. Water gets into cracks, freezes and expands, making the cracks bigger until the rock breaks.
What is meant by the term basal surface of weathering?
Original: The basal surface of weathering refers to the lower boundary between the weathered and unweathered rock. It is the zone where weathering processes have penetrated to their maximum depth, often influenced by factors like water infiltration and temperature changes.
Simple: The basal surface of weathering is the line between the weathered, broken-down rock and the solid, unweathered rock underneath.
Define the weathering processes of wetting and drying and heating and cooling.
Original: Wetting and drying cause expansion and contraction in clay minerals, leading to rock fragmentation. Heating and cooling, particularly in dark crystalline rocks, cause thermal expansion during the day and contraction at night, resulting in granular disintegration or block disintegration of rocks.
Simple: Wetting and drying make rocks expand and shrink, which can break them. Heating and cooling do the same by making rocks expand in heat and contract when it cools.
What is meant by the term acid rain in weathering?
Original: Acid rain refers to rainwater that has absorbed pollutants like sulfur dioxide and nitrogen oxides from the atmosphere, forming sulfuric and nitric acids. This acidic precipitation accelerates chemical weathering by dissolving minerals, especially in carbonate rocks like limestone and marble.
Simple: Acid rain is rain with pollution that makes it more acidic, speeding up how fast rocks break down.
Define physical (mechanical) weathering and chemical weathering.
Original: Physical (mechanical) weathering is the breakdown of rocks into smaller fragments without changing their chemical composition, through processes like freeze-thaw and exfoliation. Chemical weathering involves the alteration of rock minerals through reactions with water, oxygen, and acids, leading to decomposition and new mineral formations.
Simple: Physical weathering breaks rocks into pieces without changing what they are made of, while chemical weathering changes the minerals in rocks using water, air, and acids.
How do temperatures and precipitation influence the types of weathering processes?
Original: High temperatures and precipitation accelerate chemical weathering by providing water and enhancing reactions like hydrolysis and carbonation. Freeze-thaw weathering, a mechanical process, requires temperatures to fluctuate around freezing with sufficient moisture for ice expansion in rock cracks.
Simple: Warm and wet climates speed up chemical weathering, while places with freezing and thawing cause more physical weathering like cracking rocks.
What factors affect the type and rate of chemical and physical weathering?
Original: Factors include climate (temperature and precipitation), rock type and composition, presence of vegetation, and the availability of water. For example, limestone is more susceptible to chemical weathering due to carbonation, while freeze-thaw is prominent in colder, moist climates.
Simple: The type of rock, the climate, how much water is around, and plants all affect how quickly and in what way rocks break down.
How can both chemical and physical weathering be said to be controlled by climate alone?
Original: Climate controls temperature and moisture availability, which are critical for both chemical and physical weathering. Warm and wet climates enhance chemical reactions, while climates with temperature fluctuations around freezing promote mechanical processes like freeze-thaw weathering.
Simple: Climate decides temperature and rainfall, which control if rocks break down through chemical reactions or by cracking and breaking apart.
What is the difference between a rock slide and heave?
Original: A rock slide is a rapid downslope movement of rock material along a defined surface, typically occurring on steep slopes. In contrast, heave is a slow, imperceptible movement of soil particles caused by freeze-thaw cycles, which push particles upward and allow them to settle downslope.
Simple Terms: A rock slide is fast and involves rocks sliding down a slope. Heave is very slow and involves soil moving bit by bit due to freezing and thawing.
What are the main differences between a flow and a slide?
Original: A flow involves a mixture of water, soil, and debris moving chaotically down a slope, with no clear sliding surface. It typically occurs at higher moisture levels and lower slopes. A slide involves a cohesive mass of material moving along a well-defined plane, often triggered by factors like undercutting or increased water content.
Simple Terms: A flow is messy and happens when wet soil and rocks move down a slope. A slide is more organized, with material sliding together along a clear path.
How can mass movement processes affect the shape of slopes?
Original: Mass movement processes such as flows, slides, and falls can reshape slopes by steepening upper parts, flattening lower parts, and creating scarps and debris deposits. These movements can also lead to the formation of terraces, gullies, or accumulations of loose material at the slope base, altering the overall slope profile.
Simple Terms: Mass movements can change slopes by making them steeper or flatter and by leaving piles of rocks and soil at the bottom.
What conditions lead to solifluction, and how does it occur?
Original: Solifluction occurs in cold climates with permafrost or seasonally frozen ground. It happens when the upper layer of soil thaws and becomes saturated, allowing it to slowly flow downslope over the still-frozen subsoil. This process is common in tundra environments and leads to the formation of lobes and terraces on slopes.
Simple Terms: Solifluction happens in cold places when the top soil gets wet and slowly slides over the frozen ground underneath.
Why does soil creep occur at very low velocities?
Original: Soil creep occurs at very low velocities due to the gradual and continuous movement of soil particles under the influence of gravity. Factors such as freeze-thaw cycles, wetting and drying, and biological activity (like the movement of roots or burrowing animals) contribute to this slow process, causing particles to move incrementally downslope.
Simple Terms: Soil creep is super slow because tiny bits of soil move a little at a time, often due to freezing and thawing or when soil gets wet and dries.
How does soil creep affect the shape of a slope over time?
Original: Over time, soil creep leads to the gradual smoothing and rounding of slopes. It can cause fences, walls, and trees to tilt downslope, create terracettes (small ridges), and lead to the bending of tree trunks. This slow process subtly alters the slope profile, making it more uniform.
Simple Terms: Soil creep makes slopes smoother and can cause things like fences and trees to lean downhill.
What conditions lead to rock falls, and how do they occur?
Original: Rock falls occur on steep slopes or cliffs where the cohesion between rock masses is weakened by factors such as freeze-thaw cycles, physical weathering, and tectonic activity. When the shear strength of the rock is exceeded, individual rock fragments detach and fall freely down the slope, often accumulating as talus at the base.
Simple Terms: Rock falls happen on steep slopes when rocks break loose and drop straight down, usually due to weathering or freezing and thawing.
How do landslides and rock slides impact slopes?
Original: Landslides and rock slides significantly alter slopes by removing large volumes of material rapidly, steepening upper slopes, and depositing debris at lower elevations. They create scarps at the head of the slide and chaotic deposits at the toe, potentially blocking rivers and forming natural dams. The disruption of vegetation and soil structure also makes slopes more susceptible to further erosion.
Simple Terms: Landslides and rock slides change slopes quickly by moving lots of soil and rocks, making parts steeper and leaving piles at the bottom
How do rock type and structure influence slope development?
Original: Resistant rocks, such as granite, maintain steeper and more stable slopes due to their higher shear strength and lower susceptibility to weathering. In contrast, weaker rocks like shale and sandstone erode more easily, leading to gentler slopes. The presence of joints, bedding planes, and faults also dictates how slopes evolve, with well-jointed or layered rocks more prone to sliding along these planes.
Simple Terms: Hard rocks keep slopes steep, but softer rocks wear away faster and make slopes gentler.
How can human activities affect slope form and stability?
Original: Human activities such as deforestation, construction, mining, and road building can destabilize slopes by removing vegetation that stabilizes soil, increasing water infiltration, and altering natural drainage patterns. Excavation and undercutting for roads can steepen slopes beyond their natural angles of stability, triggering landslides and erosion. Additionally, the weight of structures and vibration from traffic can exacerbate slope instability.
Simple Terms: Cutting down trees and building roads can make slopes weaker and more likely to slide or erode.
How and to what extent can human activities affect the shape and form of slopes?
Original: Human activities can significantly alter slopes by decreasing or increasing their stability. Mining, quarrying, and construction can destabilize slopes by removing material or creating steep, unsupported faces. Deforestation reduces root support, while diverting drainage channels can increase water infiltration and erosion. In contrast, stabilizing efforts such as reforestation and engineered supports can enhance slope stability.
In simple terms: Human activities like mining, cutting down trees, and building roads can make slopes weaker and more likely to collapse. Changing how water flows can also cause more erosion and landslides. However, planting trees and building support structures can help make slopes stronger.
How can human activity decrease the stability of a slope, based on case studies?
Original: Human activity, such as urban expansion and deforestation, has decreased slope stability in areas like Rio de Janeiro and Hong Kong. In Rio, unchecked deforestation and poor urban planning have led to landslides, with steep slopes becoming more vulnerable due to heavy rainfall and soil erosion. Similarly, in Hong Kong, rapid urbanization on unstable slopes has triggered deadly landslides.
In simple terms: In places like Rio de Janeiro, cutting down trees and building too much on hills has made slopes weaker, causing landslides. In Hong Kong, building on unstable land without enough support has also led to deadly landslides.
What strategies can be used to modify slopes so they are less prone to mass movement?
Original: Slope stability can be improved through several strategies: Grading involves reshaping slopes to a gentler angle to reduce stress. Hydrogeological methods lower water levels within slopes by installing drainage systems, preventing water buildup that can trigger landslides. Mechanical methods include rock netting, ground anchoring, and pinning to physically support unstable slopes. Additionally, stepwise netting can stabilize the surface by securing a wire mesh to the slope. These strategies help prevent mass movements effectively.
In simple terms: To make slopes safer, we can flatten them to reduce stress, add drains to stop water from making them slippery, and use nets or anchors to hold the soil in place. Planting vegetation can also help keep the soil stable.
