Living with tectonic hazards (3) Flashcards
1
Q
What is a volcano and where can we find them?
A
- a volcano is a landform formed by magma ejected from mantle on earth’s surface
- found mainly along convergent or divergent plate boundaries
- a few found far away from plate boundaries (hotspots)
- most volcanoes found along the Pacific Ring of Fire
2
Q
Parts of volcano
A
- magma chamber
- vent
- pipe
- crater
- secondary cone
3
Q
Magma chamber
A
-refers to a reservoir of molten rock located beneath the earth’s crust
4
Q
Vent
A
-refers to openings in the earth surface with a pipe leading into the magma chamber
5
Q
Pipe
A
-refers to the passageway through which magma rises
6
Q
Crater
A
-refers to bowl-shaped opening at top of volcano
7
Q
Secondary cone
A
- during formation of volcano, vent may be blocked
- forces magma to find a new exit route to the surface
- a secondary cone of newer volcanic material will then form
8
Q
How are volcanoes formed?
A
- about 25 to 150km below earth’s crust, rocks melt (due to subduction) due to high heat and these molten rocks are known as magma
- magma and gases such as hydrogen and carbon dioxide will rise towards earths surface, form magma chamber
- when cracks and fractures are formed, magma from magma chamber rises to surface thru the vent
- magma is ejected onto the earth’s surface as lava
- hot and liquid lava then piles up arnd the vent in successive layers to form a volcano
9
Q
Two types of volcanoes
A
- stratovolcano
- shield volcano
10
Q
Stratovolcano: Where are they found?
A
-along convergent boundaries
11
Q
Stratovolcano: Examples
A
- Mount Fuji, Japan
- Mount Vesuvius, Italy
12
Q
Stratovolcano: Characteristics
A
- conical shape
- steep slopes
- higher in height
- secondary cones
- narrow base
- powerful eruptions
13
Q
Stratovolcano: How are they formed?
A
- developed from successive eruptions lava and ash
- ash deposits contain coarser rock fragments ejected from the vent
- after initial eruption, subsequent eruption ejects lava which covers soft ash and prevents it from being eroded
14
Q
Shield volcano: Where are they usually found?
A
-along divergent boundaries
15
Q
Shield volcano: Examples
A
Mauna Loa, Hawaii
16
Q
Shield volcano: Characteristics
A
- broad base
- gentle slope
- lower in height
- non-explosive eruption
17
Q
Shield volcano: How are they formed?
A
- formed when low-silica or basic lava is ejected
- basic lava flow easily, spreads over a large area before solidifying
- with successive eruptions, base of volcano increases in size as lava accumulates
18
Q
How and why are shape of volcanoes different?
A
- dependent of viscosity of lava (thickness/stickiness)
- acidic/high silica vs basic/low silica lava
19
Q
Acidic/ high silica lava
A
- higher viscosity, thicker, stickier
- move slowly
- does not flow far
- loud explosions
- produces steep-sided volcano
- produced at destructive boundary
20
Q
Basic/low silica lava
A
- lower viscosity
- move rapidly
- flows far
- quiet explosions
- produce gentle-sloping volcano
- produced at constructive boundary
21
Q
What is released during a volcanic eruption?
A
- lahar
- pyroclastic flows
22
Q
Lahars
A
- volcanic mudflows created when water (from rain or melt water from glaciers) and ash mix
- contain more rock debris (60 to 90 percent) compared to pyroclastic flow
- can travel much further than pyroclastic flow (50 miles from volcano)
- can move at the speed of a freight train (20 to 40 miles per hour)
- overflows riverbanks, sweep away roads and towns
23
Q
Pyroclastic flows
A
- avalanches containing hot volcanic ash and volcanic bombs
- hot, heavy cloud of ash and gases roll above and races ahead of flow
- on steep volcanoes pyroclastic can reach speeds of 100 miles per hour
24
Q
Risks of living near volcanoes
A
- Destruction
- landslides
- pollution
- change in temp
25
Q
Destruction
A
- volcanic materials produced by volcanic eruptions include lava and rock fragments or volcanic bombs
- lava with high temperatures of between 500 to 1400 degrees burns the areas it flows thru
- low silica lava moves rapidly and flows over long distances, causing damage to larger areas
- pyroclastic flow destroys everything in its path with hot rock fragments travelling at speeds greater than 80km/h
- exposure to hot gases and ash can result in serious injury or even death
- e.g Pompeii
26
Q
Landslides
A
- can range from a few rock fragments falling from the volcano to landslides of several hundred of cubic kilometres
- have the potential to obstruct river flow, causing floods, blocked roads and buried villages, farmlands
- e.g. erruption of Nevado de Ruiz in Andes Mountain released a pyroclastic flow, mixed with glacial ice, triggered lahars , killing more than 20000 ppl in 1985
27
Q
Pollution
A
- volcanic eruptions can release gases such as carbon an hydrogen monoxide, sulphur dioxide, carbon dioxide
- ash particles ejected during a volcanic eruption has the potential to :
1. eventually settle on ground, block sunlight, suffocate crops, cause severe respiratory problems for ppl and animals
2. be carried by wind to areas further from the source, disrupt daily lives - e.g. eruption of Eyjafjallajokull in Iceland 2010 produced extensive volcanic ash clouds containing tiny particles of abrasive glass, sand and rock
- caused the closure of air space over much of Europe
- airline industry suffered a loss of US$ 1.8 billion
28
Q
Change in temperature
A
- sulphur dioxide (from eruption) may react with water vapour and other chemicals in atmosphere to form sulphur-based articles
- these articles reflect the sun’s energy back into space and temporarily cool the earth for periods of time
- e.g. mt Pinatubo eruption in June 1991 caused global temp to drop by about 0.5 degrees between 1991 to 1993
29
Q
Why do people continue living near volcanic areas despite risks?
A
- source of fertile soil for farming
- source of raw materials
- source of tourism/ revenue
- source of energy
30
Q
Source of fertile soil for farming
A
- lava and ash from volcanic eruptions break down to form fertile volcanic soils (favourable to agriculture)
- e.g. the volcanic soils of Java and Bali in Indonesia support the cultivation of crops like tea, coffee and rice
31
Q
Source of raw materials
A
- volcanic rocks can be rich in precious stones and minerals
- can only be extracted after the upper layers of volcanic rocks are eroded (after millions of years)
- e.g diamonds are heated and pressurized carbon that is cooled in magma pipes beneath earth’s surface
- when refined it is used as industrial tools, in scientific research and as jewellery
- e.g. volcanic rocks are also good resources for building materials and production of other daily items
- in East Java (Indonesia), workers collect sulfur from active volcanoes
- used to make matches, fertilizers and refine sugars
- job opportunities for locals, income is higher, pay more taxes, overall economy benefits
32
Q
Source of tourism/revenue
A
- volcanic areas provide a variety of activities for tourists to engage in
- many people visit the volcanoes to hike, camp or enjoy the scenery
- e.g. the Roman town of Pompeii Italy was buried by layers of ash from the nearby Mount Vesuvius when it erupted in 79CE, killing about 2000
- unearthed site revealed buildings, pottery and mosaics intact
- abt 3 mil ppl visit every year, creating jobs in tourism industry, income higher, country economy benefit due to taxes
33
Q
Source of energy (alternative energy)
A
- when groundwater comes into contact with hot rocks beneath the surface, heats and erupts as hot water or steam
- can be harnessed to drive turbines and produce electricity
- e.g. most of Iceland’s electricity is generated from geothermal energy because of the large number of volcanoes in the country
- over 70 percent of the homes in Iceland are heated by volcanic steam
