DBH 3.
BIOLOGY & GEOLOGY
Internal geological processes
The internal dynamics of the Earth has a result different geological phenomena known as internal geological processes. The main ones are: volcanism, seismicity, mountain formation and rocks deformation.
VOLCANOES
Volcanoes are openings in the Earth´s crust through which magma flows from inside the planet to the surface. Magma is an extremely hot mixture of molten minerals which contains different amounts of water, gases and small pieces of solid rock.
Although in the mantle the temperature is extremely hot, the high pressure keeps the rocks in solid state. however, in some places the temperature is slightly higher or the crust is thinner and exerts less pressure. In these conditions, rocks start to melt and magma is formed.
Molten rocksare lighter than solid rocks and they tend to rise up. If this magma finds an exit to the surface, a volcanic eruption occurs.
a) Parts of a volcano
ACTIVITIES
Search for new vocabulary and build up a particular section of related vocabulary.
1. Do an outline with the most important ideas of this topic.
2. Answer these questions:
a. What are the factors that determine the explosiveness of a volcanic eruption?
b. What is the difference between a fumarole and a geyser?
c. What criterion is used to classify the pyroclastic materials?
d. Is it the same magma and lava? Why?
3. Draw a volcane, identify its parts and define all of them:
4. Define these words:
a. Pyroclast.
b. Icelandic volcano.
c. Explosive eruption.
5. Identify and order the following pictures from lower violent eruptions to higher one.
b) Volcanic materials
When a volcano erupts, it expels different kind of materials:
- Gaseous materials. Gases are released from magma when it reaches the surface. The main volcanic gases are water vapour, carbon dioxide and sulphides of hydrogen and nitrogen.
- Liquid materials. The magma without gases is called lava.
- Solid materials. The are known as pyroclasts. They are solid fragments wrenched from volcanic cone during the erption. they can be very large (vocanic bombs and blocks), gravel sized (lapilli) and dust sized (ashes).
c) Types of volcanic eruptions
Magma is classified according to the amount of gases and the type of minerals it contains. The type of magma determines the type of eruption and the type of volcanic cone that is formed as a result.
- Effusive eruptions
In this kind of eruptions, the magma is very fluid and forms extensive lava flows. The accumulated gases easily escape from it and eruptions are very mild. The do not produce pyroclasts.
The crater of these volcanoes can be:
- A typical opening. Thy are known as hawaiian volcanoes.
- A large longitudinal fissure, as in the case of oceanic ridges. They are known as iceland volcanoes.
- Explosive eruptions
In this case, the magma is viscous. Geses cannot escape easily from it and eruptions are violent, with explosions that produce a large amount of pyroclasts, gases clouds and lava flows. In the most extreme eruptions, very destrutive clouds, known as pyroclasts flows, may form close to the ground and move at high speeds.
There are different types of explosive volcanoes depedning on the viscosity of the magma and their explosiveness. In order of increasing level they are: strombolian, vulcanian, plinian and pelean.
d) Low-intensity volcanism
In areas of volcanic activity near active volcanoes, it is possible to occur these phenomena:
- Smoking volcanoes (fumarolas). They are cracks that emit gases at high temperature.
- Hot springs. They are springs that emit hot water which is rich in minerals salts.
- Geysers. They are cracks that emit, from time to time, eruptios of hot mineralized water.
Animation: A volcanic eruption
