landforms/processes Flashcards
what is slab pull?
Slab pull occurs on destructive plate margins -> denser oceanic plate sinks below continental= a subduction zone as the sinking plate (‘slab’) descends into the mantle, its weight creates a gravitational force that pulls the rest of the plate behind it.
What is ridge push?
Ridge push occurs on constructive plate boundaries (plates move apart)- magma rises from the mantle and cools and solidifies= new oceanic crust-> a ridge is formed that is elevated compared to the surrounding sea floor d2 heat and buoyancy of the newly formed crust. As the ridge is higher, it means that gravity causes new crust to slide away from the ridge edge
Explain the formation of island arcs:
form on destructive plate margins (denser oceanic plate subducts beneath continental) aided by convection currents and slab pull-> subduction zone where the descending plate begins to heat up and melt as it moves deeper into the Benioff zone. The magma rises through the overlying crust due to its buoyancy= erupts on the surface forming volcanos. Over time, these create a chain of islands which often are aligned in a curved shape, forming island arcs. e.g. pacific ring of fire
processes involved in the formation of a deep sea trench:
Deep sea trenches are formed at destructive plate margins, specifically in subduction zones where oceanic plates are forced beneath continental, aided by the processes of slab pull and convection currents. Therefore, as the oceanic plate sinks into the mantle, it forms a depression in the ocean floor known as a deep-sea trench. For example, the Mariana Trench. Over time, the process of plate convergence and subduction maintains the trench’s structure and depth.
Outline the role of convection currents in plate movement:
Convection currents are driven by heat from the Earth’s core and mantle-> material in the lower mantle is less dense and lighter= rises towards the lithosphere where it spreads outwards. Eventually, as it becomes less dense, it cools and sinks downwards into the mantle again= ongoing cycle-> movement exerts force on the base of plates, causing them to move.
outline the factors which lead to the formation of mudflows/lahars:
Mudflows/lahars are associated with the rapid melting of ice and snow following a volcanic eruption and associated geothermal activity. (1) These only occur where there is a substantial amount of snow or ice, typically at high altitudes. (1) The debris is comprised of water, volcanic ash, rocks, and pyroclastic flurry. (1) The lahar will typically flow down a valley side and river channel valleys. (1)
Outline the processes involved in the formation of young fold mountains:
Young fold mountains occur on collision plate margins as two continental plates move towards each other and collide, creating immense pressure and build up that means sediment and rock is forced upwards, creating fold mountains such as the Himalayas. This occurs due to the collision of the Indian and Eurasian plates.
Explain the formation of rift valleys:
form on constructive plates (2 continental plates move apart)-> earth’s brittle crust fractures as it is stretched and thinned. As vertical fractures form, one block of rock slides downwards relative to another= areas of crust drop down between parallel faults due to gravity- forming a valley, while surrounding areas elevate either side, forming a rift valley.
BUT crust is much thinner in these areas-> magma rises towards the lithosphere (convection currents)= volcanos
e.g. The east african rift valley
explain the formation of oceanic ridges:
formed on constructive plate ( plates move apart)-> magma that rises from the mantle fills this gap (less dense than surrounding rock- aided by the process of convection currents) As the magma reaches the surface, it cools and solidifies=new oceanic crust. Over time, this continuous movement of plate pushes older crust outward, widening the ridge and forming parallel bands of oceanic crust on either side d2 sea floor spreading-submarine volcanos are common e.g. cocos ridge.
explain the process of sea floor spreading/evidence of this:
SFS occurs as molten rock in the mantle rises towards the lithosphere along mid-atlantic ridges (convection currents) As the magma reaches the ocean floor, it cools and solidifies= new basaltic crust, meaning as more magma erupts and solidifies, older crust is pushed away from the ridge. This continuous process causes the oceanic plates on either side of the ridge to move apart= expanding ocean basin over time. As new crust forms, iron-rich minerals within the rock align with Earth’s magnetic field-> symmetrical patterns of magnetic stripes on either side of the ridge= evidence of sea floor spreading.
Explain the formation of a hotspot volcano:
Hotspots= localised sources of high heat energy-> volcanic activity (mantle plumes heat the crust, causing melting rock to form magma) As this material is less dense than surrounding rock it rises towards the lithosphere (d2 convection currents)-> magma is erupted= volcanic activity. As tectonic plates continue moving, old volcanoes drift away from the plume and become inactive, while new volcanoes form directly above the hotspot-> island chains e.g. Hawaiian Islands
