Unit One
Volcanoes
Class notes:
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formation of volcano occurs as a result of plate movements
volcano occur where ever the plates are thin or weak
there is a strong spatial association between volcano and plate boundaries
some volcano – ie Hawaiian Islands are formed over a Hot Spot in the middle
of the Pacific Plate. – as the plate moves NW a chain of islands is formed –
NW- SE
What is a Volcano:
 A lava tube through which molten magma forces its way
upwards
 The vent / crater which is the upper end of the lava tube
through which gas and lava erupt
 The accumulation of lave materials such as lava, ash and rock
fragments around the vent.
lava is magma which reaches the surface
two main types of lava and each produces different types of volcano.
o 1. Acid lava or viscous lava. – sticky – slow moving lava
o produced along destructive plate boundaries
o this lava moves slowly down the side of the cone and eventually cools
to form steep sided cones
o 2. Basic lava – is thinner and more fluid – it moves more quickly
results in the formation of shield / basaltic lava volcano
most commonly found along constructive plate zones, where magma
rises directly from the mantle
Composite Cones:
- formed by alternative eruptions of lava and ash
- generally steep sided
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sometimes magma rising towards the earth’s surface may become trapped in
the crust
cools very slowly and hardens into rock – granite
over long periods of time – erosion leads to the exposure of these igneous
rocks – large masses of this intrusive volcanic rock is known as batholiths
a dyke is formed when erosion exposes magma that has solidified in the
fissures before reaching the surface
a sill is lava that hardens between layers of sedimentary rocks
a neck / a plug is lava that has hardened in the vent of a volcano and is then
exposed after erosion
Impacts:
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more than 500 million people live in regions around active volcanoes despite
the possible dangers
impacts of volcano will vary – type of volcano
Volcanoes Notes
Unit One
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violence of the eruption
preparedness of the population
eruptions may cause spectacular changes in landforms in a very short time –
Mt St Helens
large eruptions may result in short term weather changes – because of the
amount of ash and smoke released into the atmosphere reduces that amount of
sunlight reaching the earth’s surface
in the year after the Mt Pinatubo eruption in 1991, global temperatures
dropped by nearly 1 degree C
there is a spatial variation in the risks to people from an eruption
1902 – Caribbean island of Martinique, a pyroclastic flow generated by
eruption of Mt Pelee – swept down the mountain and killed 29,000
a lahar after the 1985 eruption of Nevada del Ruiz in Columbia killed 25,000
people in the township of Amaro
Mt St Helens – killed 61 – mostly through the release of poisonous gasses
Benefits:
 volcano soils can be very fertile – providing livelihood for millions of farmers
 volcano rocks are young rocks and can be rich in minerals
 potential source of renewable energy from hot springs associated with volcano
 places like Italy, New Zealand, Iceland Japan generate power from this source
 more land can be created – Heimaey & Hawaii
 volcano sites act as tourist locations – spectacular scenery
 knowledge we gain from scientific observation of volcano activity
 employment - volcanologists
Activities:
1. Produce an overlay map showing the distribution of volcanoes.
2. Describe the distribution of this global phenomenon.
3. Describe the degree of spatial association and spatial interaction that exists
between plate boundaries and the distribution of volcanoes.
4. Clearly mark the location of Mt St Helens, Mt Pinatubo, Nevada del Ruiz, Mt.
Fuji, Helgafell (Heimaey) and Mauna Loa (Hawaii) on the map.
5. Carefully sketch Figures 4.5.18, 4.5.19 and 4.5.20 into your books and label
the different volcanic features of these sketches.
6. Describe the factors contributing to the development of volcanoes as a global
phenomenon. Classify the factors using SHEEP†, or another classification
system. Identify criteria that you could use to evaluate each factors relative
importance and apply this criteria.
7. Based on your response to question 6 describe the most and least significant
factors contributing to the development of volcanoes.
8. Copy table 4.5.21 ‘Impacts of Volcanic Activity.’
Volcanoes Notes