Chapter 2 Living with Tectonic Hazards - Risk or Opportunity

GATEWAY 1: Why are some areas prone to tectonic hazards? What is a natural hazard? ● A natural azard ​ is a naturally occurring event that threatens human lives and causes damage to property. ● Tectonic hazards ​ are caused by plate movements when continental crusts and ocean floors move. ○ They can include earthquakes or volcano eruptions. ● Climate hazards ​ are caused by severe and extreme weather and climate conditions. ○ They can include floods or storms. Internal structure of the earth Crust Lithosphere = Crust + Uppermost Mantle Oceanic Continental Location ● Beneath deep oceans ● Beneath Earth’s continental land masses and under shallow seas close to continent Thickness ● Between 5 - 8 km ● Between 35 - 70 km Density ● Heavy, dense. ● Lighter rock. Minerals ● Mainly basalt. ● Granite Age of Rock ● Less than 200 million years old. ● Wide range from very recent to 4 billion years old. Mantle Upper Mantle Lower Mantle ● 800C to 3000C ● 2900km thick ● Mostly solid rock that flows under high temperature and pressure. ● Layer of solid rock + asthenosphere ● Solid rock Core Outer core Inner Core ● Central part of Earth ● 3500km thick ● 3000C to 5000C ● Mainly liquid ● 2100 km thick ● Solid ● 1400 km thick What are tectonic plates? ● Tectonic plates are solid slabs of rocks which are made up of the continental crust or oceanic crust or both, attached on its underside to the upper part of the mantle. ● Edges of these plates are called plate boundaries. ● Important plates are, ​ NA Plate, SA Plate, Pacific Plate, African Plate, Eurasian Plate, Indo-Australian Plate, Antarctic plate How and why do plates move? ***FAQ*** ● Tremendous heat found in Earth’s core causes rocks in mantle to melt and become magma. ● Liquid mantle material, called magma, is intensely heated and expands, rising up. ● Rising and spreading lava pulls the plates apart, causing them to diverge as they are dragged along and move away from each other. ● Then the magma cools and sinks, pulling the plates along. ● The sinking mantle material heats up again as it nears the core, creating a convection current and causing the whole process to repeat. Notes by some weirdo called Conrad Soon.. I don’t guarantee the full accuracy of the information here. Special thanks to Mrs Wong, the most wholesome and pure Geography ahma.

Different types of plate boundaries Divergent plate boundaries ● Oceanic-oceanic plate divergence ○ Associated landforms are ​ mid-ocean ridges ​ and volcanic islands. ■ Mid-Atlantic Ridge ​ where the ​ North American and Eurasian plates diverge. ■ Iceland ​ and the ​ Azores ​ examples of volcanic islands formed. ○ As the two oceanic plates move apart, they form fractures at the plate boundary. ○ The magma wells up from the zone of divergence, cools and solidifies to form a ridge of new seafloor known as a mid-oceanic ridge. ○ The plate boundary where divergence occurs is called a constructive plate boundary. ○ As the plates move apart, the ridges move away from the spreading zone and new ridges are formed. ○ Therefore, the youngest ridges are closest to the spreading zone and oldest are further away from it. ○ The rows and rows of ridges spread out from the zone of divergence in a process known as ​ seafloor spreading ​ , creating new seafloor. ○ At various points along the mid-oceanic ridge, magma may build up and solidify to form undersea volcanoes. ○ When these volcanoes grow above sea level, they form ​ volcanic islands ​ like the Azores. ● Continental-continental plate divergence ○ Associated landforms are ​ rift valleys and block mountains. ■ East African Rift Valley ​ is an example of a rift valley formed by the divergence of the Nubian and Somalian boundaries of the African plate. ○ When two continental plates diverge, the rocks at the boundary start to stretch and fracture due to tensional forces, creating normal faults. ○ The land between the two plates move apart and a central block of land between two parallel faults can sink downwards, creating a rift valley. ○ This process also creates ​ block mountains ​ , a block of land with steep slopes but usually with a flat top, as the surrounding land sinks downwards, causing it to be left standing higher than the surrounding land. Convergent plate boundaries ● Oceanic-continental plate convergence ○ Associated landforms are ​ oceanic trenches ​ , ​ fold mountains ​ and ​ volcanoes ​ . ■ Peru-Chile Trench and Andes Mountains ​ formed by the ​ ​ subduction of the oceanic Nazca plate into the continental South American plate. ■ Sunda Trench, Barisan Mountains ​ formed by the subduction of the oceanic Australian plate into the continental Eurasian plate. ○ Oceanic plate is thinner and denser, while continental plate is thicker and lighter. ○ As a result, the oceanic plate subducts under the continental plate ○ Downward movement of the plate can be violent, producing seismic shocks known as earthquakes as the friction created between the two moving rock masses accumulates and is suddenly released. Notes by some weirdo called Conrad Soon.. I don’t guarantee the full accuracy of the information here. Special thanks to Mrs Wong, the most wholesome and pure Geography ahma.

○ The downward movement of the oceanic plate dips into the mantle and may produce a long and deep oceanic trench ■ Peru-Chile trench off the South American coast caused by the subduction of the Nazca plate into the S.A plate. ○ Downward movement of oceanic plate may cause the melting of mantle material above it, which produces magma. ○ The magma escapes through any breaks or fractures, and when it escapes through vents in the surface, it forms a volcano. ○ When continental plate rides over the oceanic plate, its edges and sediments near the edge are compressed and folded to form fold mountains ● Oceanic-oceanic plate convergence ○ Associated landforms are ​ oceanic trenches ​ and volcanic islands ​ . ■ Mariana Trench ​ and ​ Mariana Islands caused by the subduction of the denser Pacific plate into the less dense Philippine plate. ○ When two oceanic plates collide, the denser oceanic plate will subduct under the less dense oceanic plate. ○ A deep ocean trench is formed at the point of subduction. ○ The subducted oceanic plate causes the mantle material above it to melt and form magma. ○ This magma then rises through the crust and forms volcanoes, eventually, a chain of subduction volcanoes is formed. ○ Earthquakes may also occur due to the accumulation in tensile stress due to continuous friction between the two plates being suddenly released as seismic energy. ● Continental-continental plate convergence ○ Associated landforms are ​ fold mountains. ■ Himalayas in Northern India ​ are formed by the convergence of the Indian plate into the Eurasian plate. ○ When two continental plates collide, due to their similar densities they do not subduct and instead merely push into each other. ○ The resultant compressional force creates immense pressure which causes the rocks to buckle and fold, resulting in the formation of fold mountains. ○ There is no volcanic activity as there is little to no subduction of plates. Transform plate boundaries ● Transform plate boundary ○ Associated landforms are ​ transform faults. ■ San Andreas faultline ​ caused by the Pacific and North American plates sliding past one another. ○ At a transform plate boundary, two plates slide past each other. ○ This sliding action causes them to grind against each other and experience friction. ○ This friction accumulates as tensile energy which can be suddenly released as seismic en