Flashcards
Constructive (divergent) Margins
Flashcards do conjunto (20)
- 1What happens when plates move apart in oceanic areas?Produces Mid-Oceanic ridges
- 2What happens when plates move apart in continental crust?Produces rift valleys
- 3What is the space between diverging plates filled with? Therefore what does this prove about constructive margins?Filled with basaltic lava upwelling from below. Constructive margins are therefore some of the youngest parts of the Earth’s surface, where new crust is continually being created.
- 4What are oceanic ridges? Length and heightOceanic ridges are the longest continuous uplifted features on the surface of the planet, and have a total length of 60,000km. In some parts they rise 3,000m above the ocean floor.
- 5What do convection currents diverging result in?Causes the plates to also diverge
- 6What does the diverging create?This creates a gap between the plates, which leaves room for magma to rise up in it and over the crust.
- 7What happens when the magma rises?This magma then solidifies and forms a new crust
This process repeats many times and is the process of forming mid-oceanic ridge. - 8What is ridge push?Ridge push occurs when the weight of the ridge pushes the rest of the tectonic plate away from the ridge.
- 9What is slab pull?Slab pull – the weight of the tectonic plate is subducted below the overlying plate, dragging the rest of the plate with it. The precise form appears to be influenced by the rate at which the plates separate:
- 10Slow rate of slab pull (10-15mm annually):As seen in parts of the mid-atlantic ridge, produces a wide ridge axis (30-50km) and a deep (3,000m) central rift valley with inward facing fault scars.
- 11Intermediate rate of slab pull (50-90mm annually):Such as that on the Galapagos ridge (Pacific), produces a less well-marked rift (50-200 m) with a smoother outline.
- 12Rapid rate of slab pull (>90mm annually):(>90mm per year), such as on the east Pacific rise, produces a smooth crest and no rift
- 13What also occurs along the ridge?Volcanic activity also occurs along the ridge – forming underwater volcanoes which can rise about sea level.
- 14Why aren't the volcanoes large?These are volcanoes with fairly gentle sides because of low viscosity of basaltic lava. Eruptions are frequent but relatively gentle.
- 15Give an example of volcanoes formingThe Reykjanes formation is a section of the Mid-Atlantic Ridge, which bisects the Atlantic Ocean.
At its base the volcano is approximately 30 miles (50 kilometers) across. The peak contains a depression known as a caldera that is 6 miles (10 kilometers) wide. - 16What happens as new crust forms?As new crust forms and spreads, transform faults occur at right angles to the plate boundary. The parts of the spreading plates on either side of these faults may've at different rates, leading to friction and ultimately to earthquakes. These tend to be shallow focused, originating from the surface.
- 17Where do rift valleys form?At constructive margins in continental areas, such as east Africa, the brittle crust fractures as sections of it move apart. Areas of the crust drop down between parallel faults to form rift valleys.
- 18Where is the largest rift valley?The largest of these features is the African rift valley which extends 4,000km from Mozambique to the Red Sea. From the Red Sea it extends north to Jordan, a total distance of 5,500km.
In some areas, the inward-facing scarps are 600m above the valley floor and are often marked by series of parallel step faults - 19What is this region also associated with?The area is also associated with volcanic activity (e.g. highest mountain in Africa, Mt Kilimanjaro).
- 20Why is this?The crust here is much thinner than in the neighbouring areas, suggesting that tension in the lithosphere is causing the plate to thin as it starts to split. The line of the African rift is thought to be an emergent plate boundary, the beginning of the formation of a new ocean as eastern Africa split away from the rest o the continent.
Informações
- Descrição
- A2 A2 Geography (Tectonics) FlashCards sobre Constructive (divergent) Margins, criado por Alice Kimpton em 14-11-2016.
- Criado por
- Alice Kimpton · nov 2016
- Atualizado
- 18 jan 2017
- Visualizações
- 10
- Avaliação