Natural Disasters-Volcanic Eruptions

Topic 4-Lesson 1

Introduction Volcanic eruptions can cause catastrophic

damage. On November 13th 1985 the volcano Nevado del Ruiz erupted in Colombia, South America. This eruption killed 23,000 people!

IntroductionDetailed warnings

had been given but ignored. Lessons from this eruption have been used to educate local governments, police and military officials so evacuations procedures can be carried out in future to save lives.

Plate Tectonics and VolcanoesMost volcanoes are found along plate

boundaries. They occur where plates collide and separate. Edges of crustal plates can be plotted by using the locations of volcanoes. These volcanoes are generally explosive.

Plate Tectonics and VolcanoesSome volcanoes are found towards the

centre of plates. These seem to be less explosive than those found at or near plate boundaries. The Hawaiian Islands are an example of such volcanoes.

Plate Tectonics and VolcanoesAs we discussed earlier, the extinct

volcanoes found in Australia were also toward the centre of a crustal plate. Plates drift over a hot spot and leave a trail of volcanoes. In Australia they get younger as you follow them south. What direction can we infer Australia is moving from this information?

People and Volcanoes As we know, volcanoes can harm people

but they can also help us. Volcanic materials break down to form some of the most fertile soils on Earth. Because of this, people still risk living near active volcanoes.

People and Volcanoes Some other uses for volcanism include:

Volcanic products for construction materialsAbrasive and cleaning agents (pumice-foot

scrub)Raw materials for chemical and industrial

uses. (minerals such as copper, tin, gold and silver occur in volcanic regions)

Geothermal energy (Steam used to generate power in New Zealand)

Volcanoes and Volcanic FeaturesThe major factor which determines the

nature of a volcano is viscosity. (How fluid the magma is) Mafic magmas tend to be dark, low in silica and have lower viscosities allowing them to flow more freely.

See Table 1.4 pg 27 HSC Spotlight Text

Felsic Magmas tend to be lighter in colour, higher in silica and have a higher viscosity which doesn’t allow them to flow freely.

Volcanoes and Volcanic FeaturesVolcanoes found at divergent boundaries or

over hot spots tend to have free-flowing mafic lava that form lava fountains and flows.

Volcanoes and Volcanic FeaturesVolcanoes found at convergent boundaries

produce stickier more viscous felsic lava likely to be erupted violently in fragments. These fragments are called pyroclastics.

Volcanoes and Volcanic FeaturesThe explosive nature of felsic magma can

be explained because they have water and gas trapped within the magma. When deep underground they are chemically part of the magma but as they rise to the surface, pressure is reduced and they turn into bubbles within the molten material.

Volcanoes and Volcanic FeaturesMafic magmas have little water and gas

trapped within them. This is because they are less viscous which allows the gases to escape freely when the magma reaches the surface.

Volcanoes and Volcanic FeaturesSome lavas change composition during

either an eruption or the life of a volcano. Magmas can change as they rise through the crust. For example, if lavas reside in a magma chamber for a period of time, they may differentiate into separate components. Magma can also change as it interacts with rocks it comes into contact with as it travels to the surface.

Volcanoes and Volcanic FeaturesThe size and shape of a volcano depends

on the type of lava it produces. Viscous (fluid) lava produces dome shaped structures called shields. Mauna Loa is a shield volcano. These tend to be very large.

Volcanoes and Volcanic FeaturesNon-viscous lavas produce cone shaped

structures called cinder cones with steep sides. They are made of loose pyroclastic material. These tend to be small.

Volcanoes and Volcanic FeaturesComposite Volcanoes are the a mixture of

both. They are symmetrical structures formed from interbedding lava flows and pyroclastic deposits. They produce the ‘traditional’ volcanic shape.

Volcanoes and Volcanic FeaturesComposite volcanoes

tend to be the most violent. There vents have been known to be plugged by felsic lava domes that solidify. Pressure builds up beneath this dome until they explode violently like a champagne cork.

Volcanoes and Volcanic FeaturesFamous examples of such eruptions include:

Mt. Vesuvious AD 79 Destroyed the ancient city of Pompeii

Mt. St Helens USA 1980Mt. Pinatubo Philipines 1991Mt. Krakatoa Indonesia 2000’s

Some eruptions are so violent that they eject all the material away from the vent and form a crater.

Volcanoes and Volcanic FeaturesActivityComplete Activity 1.13 pg 28 HSC Spotlight

Text

Videos123

ReviewMost volcanoes are found along plate

boundaries.As we know, volcanoes can harm people but

they can also help us. Volcanic materials break down to form some of the most fertile soils on Earth. Because of this, people still risk living near active volcanoes.

The major factor which determines the nature of a volcano is viscosity. (How fluid the magma is)

The size and shape of a volcano depends on the type of lava it produces.

HomeworkRead pages 18-20 HSC Spotlight TextUpdate electronic vocabularyComplete DOT Point 4.2.1 and 4.8 pg 15

and 18

Natural Disasters-Volcanic Eruptions

Topic 4-Lesson 2

ReviewMost volcanoes are found along plate

boundaries.As we know, volcanoes can harm people but

they can also help us. Volcanic materials break down to form some of the most fertile soils on Earth. Because of this, people still risk living near active volcanoes.

The major factor which determines the nature of a volcano is viscosity. (How fluid the magma is)

The size and shape of a volcano depends on the type of lava it produces.

Volcanic HazardsBecause we can

benefit from volcanoes we need to find ways to reduce the hazards they pose to life and property. There are between 50 and 60 volcanic eruptions around the world each year.

Volcanic HazardsMost of these eruptions are away from

populated areas. Lava flows from shield volcanoes can travel quickly but usually follow valleys and their paths can be predicted. Because of this they can cause some damage but rarely are people killed.

Volcanic HazardsIt’s very different with composite volcanoes

because they erupt explosively and can send deadly materials flying. Nuee ardente is a term given to materials composed of hot gases and volcanic ash that can travel down volcanic slopes at speeds of 200 kilometres per hour. This is what destroyed the city of Pompeii.

Volcanic HazardsHuge mudflows called lahars can also be of

significant danger. When an eruption melts ice and snow on the slopes of a volcano this material can travel down slope very quickly destroying everything in its path.

Volcanic HazardsWhen a volcano under water or on an

island erupts is can produce huge waves called tsunami’s. The Krakatoa eruption generated a tsunami which was responsible for most of the death associated with this volcano.

Volcanic HazardsVolcanoes can produce poisonous gases.

Because these gases are more dense than air, the can move down valleys and asphyxiate people and animals along it’s path.

Predicting Volcanic Eruptions Because volcanoes can be so hazardous

and out of human control, we have been trying to predict where and when they will erupt to try and save lives and property.

Predicting Volcanic Eruptions Plate tectonics can be very helpful when

predicting where volcanic eruptions will occur however it’s very difficult to predict when. Look at Table 1.7 on page 22 HSC Spotlight Text and discuss the methods currently being used.

Predicting Volcanic Eruptions These techniques have been successful with

general warning however we are unable to forecast days or hours in advance. These short term predictions are essential to minimise false alarms.

Can you think of a warning system similar to this in Australia?

Predicting Volcanic Eruptions Because we cannot

accurately predict when a volcano will erupt, there is need for further research to better understand and make predictions about volcanoes. It’s a very political and economic decision to evacuate or not evacuate an area.

Predicting Volcanic Eruptions Some steps that can be taken to help

reduce the impacts of volcanic eruptions include:Increase public and official awareness of

dangersConstruct geological maps so that towns and

cities are not built on known danger areasUse geological maps to prepare evacuation

plansEnsure that dangerous volcanoes are

continuously monitored

Predicting Volcanic Eruptions Unfortunately, because

predictions are so inaccurate, there is always a danger of false alarms. For example in 1976 on the island of Guadeloupe in the Caribbean, geologists warned of an eruption and 72,000 people were evacuated. No eruption ever occurred. There have been political and economic consequences ever since.

Predicting Volcanic EruptionsActivity:Complete Activity 1.14 pg 29-30 HSC

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ReviewBecause volcanoes can be so hazardous and

out of human control, we have been trying to predict where and when they will erupt to try and save lives and property.

Plate tectonics can be very helpful when predicting where volcanic eruptions will occur however it’s very difficult to predict when.

Because we cannot accurately predict when a volcano will erupt, there is need for further research to better understand and make predictions about volcanoes.

HomeworkComplete DOT Point 4.7, 4.9 and 4.11Complete ‘To Think About’ pg 32-34 HSC

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