Non Case Study Specific 20 mark content

How do plates move?

Plate movement is driven by convection currents originating in the mantle

What are the differences between shield volcanoes and composite volcanoes?

Composite volcanoes are steep sided explosive volcanoes built by thick lava and ash like Mount Ontake

Shield volcanoes have gentle slopes formed by broad, runny lava flows

How do destructive plate margins explain the formation of composite volcanoes?

• When two plates meet such as an oceanic and continental plate the oceanic plate is denser so subducts beneath the continental plate

• As the plate moves in towards the mantle increasing pressure and temperature causes water to be released from the subducting slab

• This lowers the melting point of the overlying mantle wedge leading to the partial melting and the formation of magma

• The less dense magma rises through the continental crust and may accumulate in magma chambers before erupting at the surface

• As the lava is high in silica and high in viscosity as gases are trapped

What are the main limitations of plate tectonic theory in explaining the development of landforms associated with plate movement?

• Hotspots as the theory struggles to explain landforms created in the middle of plates, such as volcanic island chains like Hawaii

• It struggles to explain localised or complex tectonic movements, such as the movement of smaller, fragmented plates like the Anatolian plate which caused the 2023 Turkish earthquake

• Plates do not move in smooth, consistent, fluid motions; they become stuck, causing a build up of friction and episodic, irregular landscape jolts are hard to model precisely.

What are hotspots and describe the example?

• Hotspots form island chains when a stationary plume of magma, from deep in the mantle melts through a moving tectonic plate

• A hotspot stays in a relatively fixed position under the Earth’s oceanic crust, melting it to create magma

• The tectonic plate moves continuously over the stationary hotspot and as the plate moves the volcano becomes extinct and a new volcano is formed and this repeats over time to form an island chain.

• The Hawaiian islands were formed by the Pacific Plate moving northwest over a fixed hotspot creating a chain of islands

How can collision occur at plate boundaries?

• At a destructive plate boundary two tectonic plates with similarly density collide

• This means neither subducts, causing the crust to buckle, fold, and push upward, forming high mountain ranges

• Such as the young fold mountains in the Himalayas caused by the Indian tectonic plate colliding with the Eurasian plate

How can variation occur along the same plate boundary and name two examples?

• Along the same plate boundary variation in the tectonic landforms which form there is common

• At the Andes plate boundary the Nazca plate is subducting under the South American Plate and the same boundary is present along the whole plate margin

• Yet the Northern Andes has more volcanic activity, the central Andes has very high mountains and a thick crust

• While the Southern Andes has more glacial erosion and fewer volcanoes

• Iceland has formed over a constructive plate boundary at the Mid Atlantic Ridge between the North American plate and Eurasian Plate

• Yet Iceland is unusually volcanic and elevated due to a hotspot beneath the ridge increasing magma supply

What has happened with storm frequency of category 4 and 5 hurricanes in recent decades and why?

• The frequency of category 4 and 5 hurricanes in recent decades has risen

• As warmer sea temperatures provide more energy (latent heat) and make the threshold of 26.5 degrees ocean temperature present for longer periods of time

• However not all regions show increased frequency and the main trend is higher intensity

What is happening with wildfire frequency?

• Wildfire frequency is increasing strongly in fire-prone regions but not everywhere

• Higher temperatures lead to drier vegetation, longer drought periods and more intense flames

• Such as Fort Mcmurray high temperatures exceeding 30 degrees and dry boreal forest led a huge fire to form

• Some regions such as parts of Europe show less consistent wildfire increase and human management can reduce risk heavily

What is the way that the risk of hazards also depends on human vulnerability?

• Hazard risk= hazard times vulnerability

• Controlled burns in Fort McMurray along with artificial intelligence cameras which can detect fires within minutes of ignition for example and the cancellations of public services and evacuation of 1.2 million for Typhoon Jebi massively reduce risk

• Thus these adaptations over time can offset the increase