Global tectonics: Earth's interior, earthquakes and global geomorphology
- Created by: sikemi__
- Created on: 01-06-21 14:38
Differences between continental and oceanic crust
- Continental is thicker (approx 35km) vs Oceanic (7km)
- Continental is older (approx 2 billion years) vs Oceanic (60 million)
- Continental is less dense than oceanic
5 landforms formed by tectonic processes
- Fold mountains
- Ocean trenches
- Rift valleys
- Ocean ridges
- Island arcs
What are the main types of plate boundaries?
- Divergent
- Convergent
- Transform
How do volcanoes form?
- When one plate moves under another (usually oceanic under continental), creating a subduction zone, high pressure squeezes water out of the rock, lowering the melting temperature of the rock
- Melted rock (magma) rises up as it is less dense than surrounding rock and collects in magma chambers
- 'Eventually, some of the magma pushes through vents and fissures to the Earth's surface' (USGS,2020)
- Becomes lava when it erupts
How do fold mountains form?
- Convergent plate boundary
- Layers of accumulated rock crumple and fold
- Himalayas = newer fold mountains (50 million years ago). These tend to be higher. - Appalachians = older fold mountains (480 million years). These tend to be smaller as they have been subjected to erosion and weathering
How do ocean trenches form?
- Convergent boundary (oceanic-oceanic or oceanic-continental)
- More dense plate subducts, forming an undersea trench
- Deepest is Marianas Trench (36,000ft below sea level)
How do rift valleys form?
- Divergent plate boundary
- Called ocean ridges in the ocean
- Continental rift valleys e.g. East African Rift
- Further deepened by erosion
- When the tensional forces are strong enough to cause the plate to split apart, a center block drops between the two blocks at its flanks, creating a rift valley
How do ocean ridges form?
- Divergent boundary
- Plates move away from each other due to mantle convection and slab pull, creating new crust as magma rises when the mantle upwells
- When eruptions happen along the boundary, lava builds up to create ridges
- As the plates move, new crust is formed
How do island/volcanic arcs form?
- Created along a subduction zone, paralleling the trench
- Subducting plate expels water, lowering the melting point and creating magma which collects in chamber
- Eventually the magma ascends, forming a chain of volcanoes as the plate moves
Name landforms formed at convergent boundaries
- Fold mountains
- Island/volcanic arcs
- Ocean trenches
Name landforms formed at divergent boundaries
- Ocean ridges
- Rift valleys
Name landforms formed at transform boundaries
- Fault lines (build up pressure due to friction creating an earthquake) e.g. San Andreas Fault
- Oceanic fracture zones (form large valleys, or trenches) e.g. Molokai fracture zone
- The Dead Sea Rift
What are the 5 types of volcanoes?
- Shield
- Composite cone
- Lava dome
- Cinder and Scoria Cones
- Other (Rhyolitic caldera complexes and mid-ocean ridge)
Characteristics of shield volcanoes
- Broad, gently sloping flanks
- Dome shape
- Built almost entirely of layers of solidified basaltic lava flows
- Most feature a central summit vent, and often flank vents, that eject low-viscosity basaltic lava that flows long distances in all directions
- E.g. Mauna Loa and Kilauea (Hawaii)
Characteristics of lava dome volcanoes
- - Often form in the craters or on the flanks of composite volcanoes but they can form independently
- - When high-viscosity rhyolitic magma flows from composite volcanoes, it solidifies quickly around a vent
- - Pressure from magma within the volcano expands the dome and eventually it erupts
- - E.g. Mount St Helens
Characteristics of composite cone volcanoes
- Steep upper flanks and a symmetrical appearance
- Alternating layers of material such as ash and cinders, blocks and lava deposited by past eruptions
- Also called stratovolcanoes
- Higher risk (explosive)
- Flying rocks and lava bombs, mudslides
- E.g. Mount Fuji
Characteristics of cinder and scoria cone volcanoe
- Simplest and smallest volcano type (usually less than 1000ft)
- Circular cone of hardened lava, ash and tephra around a single vent
- Formed when volcanic material fragments and falls to the ground after being ejected into the air from the vent
- E.g. Lava Butte, Oregon
Characteristics of rhyolitic caldera mid-ocean rid
- Ancient volcanoes that erupted so explosively they collapsed into the magma chamber beneath them, forming a giant crater, or caldera (e.g. Yellowstone)
- Mid-ocean ridges are undersea areas along tectonic plate boundaries where the plates are diverging.
What are the different volcano eruption types?
- Explosive (gas-driven explosions that propels magma and tephra)
- Effusive (outpouring of lava without significant explosive eruption)
- Phreatic (heat from magma interacting with water)
- Strombolian and Hawaiian eruptions. (least violent)
- Subplinian
What comes out of volcanoes?
- Magma/lava
- Gas (water vapour, CO2, SO2, hydrogen sulphide). Released through eruptions and fumaroles
- Pyroclastic material (tephra)
- Ash (small grain/glass)
- Bombs
- Lahars
How do hotspots form?
- - Hotspot - an area in the mantle from which heat rises as a thermal plume from deep in the Earth
- - Magma is formed by melting rock (due to pressure and temperature) and magma rises and erupts to form volcanoes
- - As the plate moves over the hotspot, the volcanoes move away and are replaced by new ones
- - Leads to chains of volcanoes like Hawaiian Islands
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