Tectonic Processes & Hazards - EQ1 - 1.1 Flashcards
How do we map the structure of the earth
- seismic waves
Why do we map the tsructure of the earth using seismic waves
- it is 6,500km to the centre of the core
- the core’s heat is expected to be 6,000 degrees celcius
What is the composition of states of matter in the asthenosphere
- 90% solid & 10% liquid
What is the asthenosphere
- it is the upper layer of the earth’s mantle below the lithosphere
- the extreme pressure & heat in this layer cause the rocks to flow like a liquid
- the rocks in the asthenosphere are not as dense as the ones in the lithosphere - allowing the movement of tectonic plates around on the Earth’s surface
What is the lithosphere broken up into
- 7 major & minor parts called tectonic plates
Tectonic plates move…
It is this movement that creates…
relative to eachother over the asthenosphere
earthquakes & volcanic erruptions
Tectonic plates are very….. that vary greatly in…& move…
large slabs of solid rock that vary greatly in size & move slowly (about 2-15 cm a year)
What is the limitation to our understanding of tectonic plates
- plate boundaries are not clearly defined, in reality we are still working at where they are exactly
- the situation is complicated by the existence of faults
What are tectonic faults
- multiple cracks which spread out from boundaries
Where are the majority of earthquakes distributed
- the majority of earthquakes (about 95%) occur close to or at a plate boundary
- many occur around the ‘Ring of Fire’ surrounding the pacfic ocean
The most powerful earthquakes are usually associated with ….. or……. plate boundaries
- convergent or divergent
Where are volcanoes found
- most active volcanoes occur at or near to plate boundaries
- about 75% occur aorund the ‘Ring of Fire’ surrounding the Pacific Ocean
- most occur at either convergent or divergent plate boundaries, or at hotspots
What is the percentage distribution of tsunamis
- over 70% of tsunamis occur around the Pacific Ocean
- 15% Mediteranean Sea
- 9% Carribbean Sea & Atlantic Ocean
- 6% Indian Ocean
Where are most tsunamis found
Since they are caused by tectonic activity, they mostly occur at convergent boundaries
Where 2 tectonic plates meet, they form a ………. - each creating ……
- plate boundary
- distinct landforms & processes
It is at ……. ……. where most tectonic activity occurs
plate boundaries
What are plate margins
- the area adjacent to plate boundaries
- they include areas either sude of the boundary that may be affected by the movement
What are the 5 different plate boundary types
- divergent
- convergent
- transform
- collision
- complex
What are the 3 categories for covergent boundaries
- oceanic & continental
- oceanic & oceanic
- continental & continental
What are the categories for divergent & conservative boundaries
- oceanic & oceanic
- continental & continental
What are divergent plate boundaries
- constructive
- plates move apart (usually oceanic)
Where are divergent boundaries most often found
- ocean ridges
What normally occurs along divergent plate boundaries
- large numbers of shallow focus & generally low magnitude earth quake events
Give examples of where diveregent plate boundaries occur
- between Nazca & Pacific Plates
What are convegent plate boundaries
- destructive
- these are actively forming collisions with late material melting in the mantle causing frequent earthquakes & volcanic erruptions
Give an example of convergent plate boundaries
- West Coast of South America
What are transform plate boundaries
- conservative
- plates moving past eachother or in the same direction & at different speeds
What are collision plate boundaries
- where 2 continental plates converge
What are complex plate boundaries
- where serveral types are found along a relatively short distance
What is an example of a complex plate boundary
- North East of Caribbean Plate
What is an example of a transform plate boundary
- Between the North Pacfic & American Plates
With conservative plates, the relative movement is….. & classified as either…
- horizontal
- sinistral (to the left)
- dextral (to the right)
With conservative plates, the lithosphere is neither….nor…..
created nor subducted
While conservative plates do not result in ……., they are sites of……
- volcanic activity
- extensive shallow focus earthquakes usually at a considerable magnitude
What do plate boundaries depend on
motion & plate type
Explain the defining characteristics of plate boundaries
-motion
- Motion - whether the plates are moving apart (divergent), colliding (convergent) or sliding past each other, (conservative or transform)
Explain the defining characteristics of plate boundaries
-plate type
Plate type: whether the tectonic plates are oceanic or continental
Decribe oceanic plates
- Oceanic plates make up the ocean floor and are high density, basaltic rock, but only 7-10 km thick
Describe continental plates
- Continental plates make up the Earth’s landmasses and are much thicker at 25-70 km but made of less dense, granitic rock
Intraplate earthquakes can occur…. - the causes of these are…
- anywhere
- not fully understood
What is the cause of intraplate earthquakes
- Tectonic stresses causing ancient fault lines to reactivate
- The plates are moving over a spherical surface and this causes zones of weakness
Give an example of an intraplate earthquake
- New Madrid Seismic Zone, on the Mississippi river generates earthquakes up to 7.5, but it is thousands of miles from the nearest plate boundary
What can also trigger intraplate earthquakes
- human activity, such as the weight of water in a reservoir, fracking of gas or large explosions
Some volcanic eruptions are ……… meaining they are distant from ………. at locations called ………
- intra plate
- a plate boundary
- mid-plate hotspots
What happens at mid-plate hot spots
- Isolated plumes of convecting heat in the asthenosphere, called mantle plumes, rise towards the surface, generating basaltic volcanoes that tend to erupt continuously
- A mantle plume is stationary, but the tectonic plate above moves slowly over it.
- Over millennia, this produces a chain of volcanic islands, with extinct ones most distant from the plume’s location.
What are mantle plumes
- concentrated areas of heat & convection where molten viscous silicate material rises from the outer core/mantle boundary to about 700 km
At plate boundaries, mantle plumes are ….-like
sheet
At hotspots, mantle plumes are ….-column like
column
Describe how intraplate volcanoes can form in oceanic plates
- these have magma, rising through the mantle from the edge of the outercore,
- that it is able to melt its way though, forcing molten material to the surface, creating volanoes that grow from the seabed
Describe how intraplate volcanoes can form in continental plates
- these are much thicker but get stretched enough in places for the magma from a hot spot (linked to a mantle plume) to breakthrough
Intra Plate Volcanoes in the Hawaii Islands
The hawaii islands have …. volcanoes which are the youngest of ….. volcanoes found along a …..km line to the north-west
- 15
- 150
- 6000
Intra Plate Volcanoes in the Hawaii Islands
………. and …………… are the most active volcanoes on the planet.
The sub-marine volcano …….. is youngest in the Hawaiian chain, being created as the ……………………………..
- Kilauea and Mauna Loa are the most active volcanoes on the planet
- The sub-marine volcano Lo’ihi is youngest in the Hawaiian chain, being created as the Pacific Plate moves north-westwards over the hot spot
Mantle plumes and hot spots
- There are ….. massive mantle plumes in the Earth’s mantle layer, one centred under the …………. plate and the other under the …………. plate.
- 2
- Pacific
- African
Mantle plumes and hot spots
From these mantle plumes ……………………. are created where magma rises through the ……………………. and sometimes breaks through the……….
- From these mantle plumes small hot spots are created where magma rises through the asthenosphere and sometimes breaks through the crust
Mantle Plumes and Hot Spots
Isolated hot spots occur where there is an………
upwelling of molten material directly from the outer core/mantle boundary to the surface (for example, the Hawaiian islands)
Explain the causes of tectonic hazards - explosive volcanoes
- volcanoes, often explosive, are found in the Andes fold mountains because unstable mantle material and melted oceanic plate force their way to the surface.
Explain the causes of tectonic hazards - gentle volcanoes
- Gentle volcanic activity is found at constructive plate boundaries as mantle material moves upwards to fill the gaps left by diverging plates
- for example, between the Nazca and Pacific plates.
Explain the causes of tectonic hazards - small earthquakes
- Constructive plate boundaries only have small earthquakes, as there is not much friction or strain as plates diverge.
Explain the causes of tectonic hazards - strong earthquakes
- Transform plate boundaries (conservative) have a large amount of friction, and when strain is released the shockwaves can be strong.
Explain the causes of tectonic hazards - largest earthquakes
- Converging plates create the largest amount of friction and strain, with earthquake focal points following the Benioff zone to considerable depths
Explain the causes of tectonic hazards - tsunami
- An upward or downward movement of the crust must disturb a mass of seawater
- This movement will be associated with an undersea earthquake, and so is usually linked to a destructive (convergent) plate boundary
