Volcanoes Flashcards
why are volcanoes found at plate boundaries?
because the movements of plates cause fissures through which volcanoes can form
what is the ring of fire?
a horse-shoe shaped zone encirclingvol the Pacific basin where 90% of the world’s earthquakes and over 75% of the world’s volcanoes occur. There are many plate boundaries in this zone.
what is the difference between magma and lava?
magma is molten rock beneath the surface of the earth while lava is magma which has reached the surface of the earth
list 5 positive effects of volcanic activity
1) volcanic areas may become tourist attractions & generate income
2) volcanic lava can contain valuable minerals such as diamonds
3) volcanic ash can act as a fertiliser
4) underground water is very hot and can be used for heat or electricity
5) hot springs attract tourists
how does a volcanic cone form?
hardened lava, ash and cinders from the volcano pile up around the vent to form a cone
list 5 warning signs that a volcanic eruption is imminent
1) series of earth tremors
2) volcano starts rumbling and lets off hot ash and[/or sulphur gas
3) rocks around the volcano heat up
4) surrounding rivers and lakes heat up, fish die
5) mountains can change in shape - a bulge may appear on the side
what is the difference between an active, dormant and extinct volcano?
an active volcano is erupting or shows signs of erupting, a dormant volcano has erupted in the past and may erupt in the future and an extinct volcano has not erupted for thousands of years
What is a batholith? Can you give an example of a well known batholith in the Western Cape?
A batholith is a huge mound of magma that cools and solidifies underground. After millions of years they may be exposed as granite domes on the earth’s surface. Example is Paarl Rock
Granite, basalt and dolerite are examples of what type of rock?
igneous rock
what is a caldera?
it is a large, basin shaped depression formed when a volcano destroys its upper part or collapses into itself. It looks like a big crater (eg Krakatau)
Mt Etna is an example of what shape of volcano?
a composite volcano - a classic, steep-sided volcanic cone formed from alternating layers of ash and lava
what is a volcanic bomb?
A volcanic bomb is a mass of molten rock formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground.
draw a diagram of a volcano showing the following features: magma chamber, main vent, secondary vent, pipe, volcanic cone , secondary cone, lava flow, ash cloud, layers of ash and lava, crust
own diagram
why is farming good in areas where there are extinct volcanoes
The rock formed by ash and cooled lava breaks down into fertile soil
does a volcano always spew lava when it erupts?
no - it may emit ash or ash and steam
