Restless Earth Flashcards
Name 2 features of continental crust
30-50km thick and made of granite (low density igneous rock)
Name 2 features of oceanic crust
6-8km thick and made of basalt (higher density igneous rock)
How are earthquakes caused at conservative boundaries?
As plates slide past each other, friction between them causes earthquakes. These are rare but very destructive
How are volcanoes formed at constructive boundaries?
As plates move apart, magma rises up through the gap. The magma is basalt and is very hot and runny. It forms lava flows and shallow sided volcanoes
How are earthquakes caused at constructive boundaries?
Earthquakes are caused by friction as the plates tear apart. These earthquakes are small and don’t do much damage
How are volcanoes formed at destructive boundaries?
As plates push together the oceanic plate is subducted. As it sinks it melts and makes magma called andesite. Sea water is dragged down with oceanic plate making the magma less dense so it rises through the continental crust. The water erupts as very explosive steam
How are earthquakes caused at destructive boundaries?
Sinking oceanic plate can stick to the continental plate. Pressure builds up against the friction. When the plates finally snap apart a lot of energy is released as an earthquake. They can be devastating, especially if shallow
Give an example of a conservative plate boundary
The San Andreas Fault
What is the Volcanic Explosivity Index?
The VEI measures destructive power of a volcanic eruption on a scale of 1 to 8
Give two advantages of the volcano Sakurajima in Japan
40% of the land is fertile volcanic soil, growing tea and rice. Hot springs and lava flows are a popular tourist attraction; the area is a national park
How many people live at the base of the volcano Sakurajima in Japan?
7000 people
Give a disadvantage of the volcano Sakurajima in Japan
The nearest city, Kagoshima, has a population of 650,000; a big eruption could devastate it with ash, lava bombs and pyroclastic flows
How are aircraft used to predict a volcanic eruption?
They measure the amount of gas given off by the volcano, which would increase as the chance of an eruption increases
How are tiltmeters used to predict a volcanic eruption?
They detect when a volcano swells up and fills with magma
How are seismeters used to predict a volcanic eruption?
They monitor earthquakes, which would increase as the chance of a volcanic eruption increases
How do concrete lahar channels protect against volcanic eruptions?
They divert dangerous mud flows
How do concrete shelters protect against volcanic eruptions?
They protect against volcanic bombs and ash
Why are tectonic hazards increased in developing countries?
People live in risky locations as there’s nowhere else to live
Can’t afford safe well-built homes so often buildings collapse
They don’t have insurance
Governments don’t have money and resources to provide aid
Poor communications so warning and evacuation may not happen
Where and when did Mount Nyiragongo erupt?
Democratic Republic of Congo in January 2002 on a constructive plate boundary - hot and runny basalt lava
What were the primary effects of the eruption of Mount Nyiragongo?
River of lava 1000m wide, 20km long flowed into city of Goma
14 villages destroyed + 12,500 homes
100 people died from lava + poisonous gas
400,000 people evacuated, many became refugees
Earthquakes triggered
What were the secondary effects of the eruption of Mount Nyiragongo?
120,000 people homeless
Little clean food + water so cholera spread
In first week UN sent 260 tonnes of food
Governments around world gave $35 million to aid refugees
By June 2002 some roads cleared and water supply repaired
What are the focus and epicentre of an earthquake?
An earthquake starts at the focus. The epicentre is the point on the Earth’s surface above the focus and is the first place to shake
What happened in the Nigata (Japan) earthquake in 2007?
In city of 90,000, 11 people died + 1000 injured
350 buildings destroyed
Tsunami warning issued but false alarm
Epicentre offshore so less shaking on land
Happened at 6pm - people alert and remembered drill
What happened in the Kobe (Japan) earthquake in 1995?
City of 1.5 million - very high population density
5000 died and 26,000 injured
Many fires started and couldn’t be reached due to collapsed buildings
Damage was $200 billion
Epicentre was close to Kobe
Happened at 6am - people were asleep and confused in the dark
