1b - Tectonics Flashcards
What are the main components of the Earth’s structure?
Crust
Mantle
Core
Describe the Earth’s crust
The crust is the solid outer layer of the Earth which is the thinnest and least dense layer
Coolest part - ranging from air temperature to 900C
Densities - ranging from 2.7-3.3g/cm3
Its divided into tectonic plates that move due to convection currents
Describe the Earth’s mantle
The asthenosphere is the mantle directly below the lithosphere which is semi-molten and viscous - solid layer under such high pressure that the rock flows
Mainly composed of peridotite
Under the asthenosphere is the liquid lower mantle
Temp range - 1000-4000C
Density - 3.4-5.6g/cm3
Describe the Earth’s core
The outer core is liquid iron and nickel with temperatures of 4000-6000C
The inner core is iron at temperatures of 5000-6000C, with such high pressures that the iron is solid
Density - 9-13g/cm3
Radioactivity and heat caused by radioactive decay of uranium and thorium
What are the types of tectonic plates?
Continental - older, less dense, mainly granite
Oceanic - newer, denser, mainly basalt
Both are less dense than asthenosphere rocks
Define lithosphere
Lithosphere - the crust and the solid upper layers of the mantle
How does convection currents contribute to plate movements?
The core heats the molten rock in the mantle making it less dense and it rises to the Earth’s surface
It cools and spreads out near the lithosphere, dragging the tectonic plates
Molten rock cools and flows back to the core to be reheated
At constructive boundaries, plate moves apart/ at destructive boundaries plates move towards one another
What are the three main types of plate boundaries?
Convergent (destructive)
Divergent (constructive)
Conservative
What happens at convergent plate boundaries?
Two plates move towards one another, colliding, and the denser oceanic plates flows beneath the continental plate (subduction)
The subducted plate melts and magma builds up, and forces its way to the surface producing a composite cone volcano
What happens at divergent plate boundaries?
The plates move away from one another
Magma rises through the gap forming shield volcanoes
New land is produced as magma cools
What happens at conservative plate boundaries?
Two plates move past one another and rub together producing lots of pressure and friction
One plate slips, causing large earthquakes
What are hotspots?
Hotspots are points on the Earth’s crust with very high heat flow, linked to increased volcanic activity
What are the types of volcanoes?
Shield
Composite cone
Describe shield volcanoes
Formed on constructive plate boundaries or hotspots
Wide volcanoes, gentle sloping sides, wide base
Formed due to less viscous/thin lava which flows a long distance before cooling
Frequent eruptions with long durations but low violence
Low explosivity - magma not held under pressure
Describe composite cone volcanoes
Formed on destructive plate boundaries
Steep volcanoes, steep sloping sides, narrow base
Formed due to layers of viscous lava that has dried near the vent
Infrequent eruptions but high explosivity - lava trapped in chamber before violently escaping
Where is the energy produced by an earthquake at its greatest?
Epicentre - the point on the surface directly above the focus
Focus - the central point of the earthquake deep under the surface, where the earthquake happens
How can tsunamis form?
By earthquakes, causing plate movements
By large meteor strikes
By underwater volcanic eruptions
Which all cause water to be displaced giving out large waves
What were the primary impacts of the earthquake in Kashmir, Pakistan?
- 7.6 Mw earthquake in 2005
- 80,000 killed + 140,000 injured
- largely due to modern building collapsing (lots of school buildings)
- during Ramadan so people asleep after pre-dawn meal
- 3.5 million people displaced
- 90% livestock killed
What were the secondary impacts of the earthquake in Kashmir, Pakistan?
- occurred in remote, steep mountainous regions causing landslides which buried people & cut off road access
- unseasonal torrential rain added to slope stresses and instability
- broken sewerage pipes -> contaminated water supply and disease
- cold harsh winter, hypothermia deaths
What were the short term responses of the earthquake in Kashmir, Pakistan?
- US marine and army helicopters from Afghanistan deployed which flew tents, basic provisions and medical supplies
- US issued $5.4bn of aid
- Due to Ramadan spirits, people brought car supplies to camps
- UN provide 2.4m blankets, 1.2m quilts and 200,000 tarpaulins
- response limited by lack of road access and poor relations with India
What were the long term planning for the earthquake in Kashmir, Pakistan?
- limited long term planning
- modern concrete construction but not of sufficient quality
- loss of skilled labourers meant that the traditional Dhaji Dewari buildings were limited
What were the primary impacts of the earthquake in Christchurch, New Zealand?
- 7.1 Mw Earthquake followed by 6.3Mw in 2011
- 185 killed - mainly from CTV building collapse
- $40bn in economic losses
- 3000 injured
- 100,000 damaged buildings and over 10,000 needed to be demolished
What were the secondary impacts of the earthquake in Christchurch, New Zealand?
- significant liquefaction leads to infrastructure loss (older building and transport systems)
- loss of tourism and finance problems
- suggested by economists that it will take 50+ years for economy to completely recover
- schools had to amalgamate
- produced 400,000 tonnes of silt
What were the short term responses for the earthquake in Christchurch, New Zealand?
- rescue crews from USA, UK, Australia and more came within 12 hours
- Australia gave $5 million in aid
- Gov declared a state of national emergency
- chemical toilets provided for 30,000 residents
- power restored within 2.5 days
- isolation tents for gastroenteritis
- missing person centre - volunteers and welfare centres for 3000 people
What were the long term managements for the earthquake in Christchurch, New Zealand?
- gov has significant seismic focus on newer buildings
- good geopolitical relationships with governments
- engineers used colour coding practice to divide Christchurch into 4 zones after the earthquake to aid in future mitigation depending on damage/usability
- many NGOs including Save the Children helped with long term recovery efforts
- Canterbury Earthquake Recovery Authority was created to organise the rebuild of the region
What were the primary impacts of the earthquake in Tohoku, Japan?
- 9 Mw Earthquake in 2011
- 667-1479 deaths - collapsed buildings
- 1000 damaged buildings
- 800 aftershocks of 4.5 Mw
- heavy damage to transport infrastructure
What were the secondary impacts of the earthquake in Tohoku, Japan?
- majority of deaths,>17,000 deaths, due to Tsunami - most aged over 65
- over 127,000 collapsed buildings & over 1.2m damaged severely due to tsunami
- Dam collapse at Fukishima led to meltdown of nuclear generators as cooling systems failed
- $300 billion economic damage
What were the short term responses of the earthquake in Tohoku, Japan?
- search and rescue teams from UK, US, New Zealand
-130,000 people displaced with many in shelters - transport and communication networks restored quickly
- tens of thousands of temporary houses built within the first 2 weeks
- Red Cross and Red Crescent provided support as did NGOs
What were the long term managements of the earthquake in Tohoku, Japan?
- advanced warning systems (Pacific tsunami Warning Centre) put in place to communicate message to public
- 1000 seismometers located in Japan (to aid prediction)
- Detected earthquake one min before it reached mainland
- huge seawall out in place to protect coastline
- good gov relationships, abundance of aid
- 140,000 evacuated
- since 2007 - Japanese smartphones fitted with Warning systems
- 1 Sept now National Disaster prevention Day in Japan - education, practice drills
