Theme 2a Plate tectonics Flashcards
(20 cards)
What is an oceanic crust
Younger, heavier, can sink and is constantly being destroyed and replaced
What is a continental crust
Older, lighter, cannot sink and is permanent
What is happen and form at constructive (divergent) plate boundary
- 2 plates move away from each other forming new oceanic crust
- Gentle volcanoes, gentle earthquakes, no fold mountain
What is happen and form at destructive (convergent) plate boundary
- Oceanic crust moves toward continental and sinks under it, and is destroyed.
- Violent volcanoes, violent earthquakes, create fold mountain
What is happen and form at conservative (transform) plate boundary
- 2 plates move sideways past each other
- No volcanoes, violent earthquakes, no fold mountain
Earthquake distribution (in terms of places, not boundary type)
- Encircle the whole of the Pacific Ocean
- Extend down the entire length of the mid-Atlantic ocean
- Stretch across southern Europe and Asia, linking the Atlantic and Pacific Oceans
Volcanoes distribution (in terms of places, not boundary type)
- Encircle the whole of the Pacific Ocean (ring of fire)
- Extend down the entire length of the mid-Atlantic ocean
- Smaller areas in the southern Europe, the Caribbean, east Africa and the mid-Pacific Ocean
Volcano features and vocab
- Craters - circular depressions that are usually less than 1 Km in diameter; formed by the explosive ejection of material from a central vent
- Calderas - huge crater caused when a volcanic cone collapses into a partly empty magma chamber after a powerful eruption
- Parasitic cones - smaller cones develop on the sides of a bigger volcano; form when the main vent becomes blocked, magma finds another outlet
- Lava domes - features that often grow on the sides of stratovolcanoes; form from very viscous lava solidifies quickly => creating steep convex sides
+ Lava domes often collapse => lead to explosive eruptions and pyroclastic flows
Lahars can be caused by ?
- Melting snows
- Heavy rainfall/water content of magma
- Mix with ash
- Flow down steep slopes/gravity
- Triggered by earthquakes
What are problems caused by lahars
- Loss of life
- Destroy buildings/ homes
- Inundate farmland/ destroy crops, livestock
- Disrupt communications
- Bring down power lines, damage water pipes
- Destroy work places, damage factories
Information about volcanoes at constructive boundary
- Most volcanoes at constructive boundaries erupt under the ocean
- The lava cools quickly to form ball shapes (pillow lava)
- These volcanoes usually occur along a rift, not from one main vent
What are volcanic plugs
Formed when lava solidifies in the pipe of an extinct volcano. Over time, the volcanic cone made up of less resistant rocks wear away, leaving behind the solidified volcanic plug.
Causes of earthquakes
- 2 plates “stick”, pressure builds up
- One plate jerks forward sending shock waves to the surface
Causes of volcanoes
- At constructive margin
- Plates move away from each other, magma rises to fill the gap.
- There might be steam or ash ejections, explosions - At destructive margin
- Oceanic crust melts from friction and heat from mantle
- Newly formed magma is lighter so it rises to the surface
The structure of a composite cone or stratovolcano
- Found at destructive plate margins with an oceanic plate
- Formed by viscous (thick) lava
- Eruption starts violently creating ash and pulverised rocks, later lava flows out
- Have alternating layers of lava and rock fragments
Ways to prevent damage or deaths by earthquake ?
- Move away from areas of instability
- Forecasting/warning to public
- Build earthquake proof buildings
- Awareness / what action to take
- Practise drills
- Emergency services organised
- Emergency food/supplies
What are the effects / difficulties of earthquakes ?
- May occur in a country with low GNP, cost
- Psychological impacts
- Devastation may cover a wide area/large-scale affects many people
- Homelessness
- Damage to infrastructure
- Damage to economy
- Impacts on food supplies/famine
The structure of a shield volcano
- Found at constructive plate margins, , mid-plate volcanoes
- Composed almost entirely of long thin lava flows, built up over a central vent
- Continuous and non-violent eruption
- Have gentler upper slopes (about 5 degrees) and steeper lower slopes (about 10 degrees)
- Has convex shape, like a warrior’s shield lying flat on the Earth
Advantages brought by volcanoes
- Geothermal power - in countries like Iceland, rocks beneath the surface are hot => hot water underground generate electricity
- Fertile soils - some types of lava and ash weather rapidly in tropical conditions => form rich, thick soil layer. abundant in trace elements
- Tourism - when safe, volcanoes attract tourists => help the economy and creates jobs
- Minerals and mining - much of the sulfur mined is from around active volcanoes; other mineral deposits by volcanoes that are now extinct
- Volcanoes creating landmass - produce new islands, enlarge existing landmasses
Dangers of volcanic eruptions
- Ash falls - can be hazard to aircraft, block the sun => cooler, damages property by burying buildings
- Pyroclastic flows - impossible for people to escape => many deaths
- Lateral blasts - explode sideways => destructive within 40 Km
- Mudflows (lahars) - more dense than water => very destructive
- Volcanic gases - causing suffocation
- Acid rain - damage buildings, serious effects on plants & species
- Tsunami
- Lava flows - destroy buildings, rarely result in death
