Volcanoes

Daneilla DesgoutteWestwood High SchoolGrade 11p

Objectives

Students should be able to:1. Define and explain the formation of a volcano.2. Differentiated between the types of lava and list features

of each.3. Label the features of a volcano.4. Differentiate between the types of volcanoes.5. List three (3) Extrusive and intrusive features and explain

there formation6. Describe how volcanic activity can affect people.

What is a volcano

Rocks below the crust have a very high temperature, but the pressure keeps the rocks in a semi solid state.

If the pressure weakens the rocks become liquid ( Magma).

Magma forces its way into cracks of the crust and may either reach the surface where it forms volcanoes, lava flow or it may collect in the crust and form batholiths, sills, dykes.

A volcano is a conical hill or mountain build up by the ejection of magma from a vent.

Types of lava

Viscous lava- 1. High in silica content 2. Light in colour3. Volcanic eruption is very loud4. Contains gas which cannot escape easily5. Does not flow fast, but cools fast6. Creates tall and steep volcanoes

Caribbean volcanoes are normally made up of viscous lava.

Basic Lava –1. Low in silica content2. Dark in colour3. Flows quietly4. Flows easily5. Spreads thin6. Cools slowly7. Volcanoes will be lower and broader

Labelled volcano

Types of volcanoes

A volcanic cone is made of either lava or a mixture of lava and rocks torn from the crust, or ash and cinders.

There are three types of volcanoes:

1. Ash and Cinder Cone2. Lava Cone3. Composite Cone

Ash and Cinder cone

In violent eruptions the molten lava is thrown high into the air.

It breaks into small particles, cools and solidifies before falling back to earth as volcanic ash.

A series of ash eruptions may build up build up and form a cone.

Lava Cones

The slope of the cone is depend upon whether the lava was fluid or viscous, when it was molten.

Fluid lavas give rise to gently sloping cones, e.g. Mauna Loa ( Hawaii).

Viscous lava give rise to steeply sloping cones.

At times the lavas are so vicious that when they are forced out of the volcano they from a spine or plug.

Composite cone

Volcano is made up of alternate layers of lava and ash.

Begins each eruption with great violence which produce layers of ash.

As the eruption continues the violence ceases and the lava pours out forming layers on top of the ash.

Extrusive features of a volcano

Basalt Plateau- Basalt lava flows, may smoother hills

and valleys of a pre-existing landscape producing a wide flat plateau. The largest basalt plateau is in India.

Geyser –Every 65 minutes the water come out

the water is pre –heated. They also form natural fountains

Hot springs- Hard rock on top of lava. The water is

then heated and the runs as hot spring.

Solfatara- An area where gases are released

from volcanoes (sulphur).

Intrusive features

These features are formed by magma that have cooled and hardened before it reaches the surface. They do come to the surface due to weathering.

1. Sill- is formed where magma flows

horizontally between two rock layers and cools. It is formed parallel to the surface.

2.Dyke- is a vertical or inclined sheet of

magma that has cooled.3.Batholith- is a underground reservoir of magma.

The rocks cool and harden below the surface. If a dyke become expose if its under a river a water falls will form.

Effects of Volcanic activity

Negative Effects: Displacement of population Destruction of crops and economy Change in weather pattern Landslides Environmental Pollution Death

Positive Effects: Valuable for minerals ,e.g. Nickel,

Copper, Gold. Fertile farming soil Hot springs, Spas Forms tourist attractions Exporting of volcanic rocks

Predictions of volcanic eruption

Seismograph Minor shacks Gradual swells in volcano Deformed rocks

Quiz

1.Magma becomes lava when it reaches a volcano’s

a. Geyserb. Pipec. Magma chamberd. Vent

2.A volcanic mountain made up of volcanic ash, cinders, and bombs is called

a) Shield volcanob) Cinder conec) Composite volcanod) caldera

3.Magma that hardens in a volcano’s pipe forms a

a) Volcanic neckb) Sillc) Volcanic craterd) Hot spot

YOUR CORRECT

IM SORRY, TRY AGAIN

Basalt Plateau

Geyser

Bocca Grande della Solfatara

Hot Spring

Reference

Jan Jenner, Ph.D. California Focus on Earth Science,2008,Pearson Education Inc.

R.B. Bunnett, General Geography in Diagrams,1985,Longman Group Ltd.