Earthquakes and Volcanoes

Volcanoes are places where molten rock called magma leaks out through a hole or a crack in the earth's crust. Magma originates from the mantle, where high temperature and pressure cause the rock to melt. When a large pool of magma if formed, it rises through the denser rock layer towards the earth's surface.

There are two main types of volcanoes, namely:

1. Fissure volcanoes: These occur along the cracks in and between tectonic plates. They can be many kilometers long. Lava is usually ejected quietly and continuously, forming enormous plains or plateaus of basaltic volcanic rock.
2. Central volcanoes: These have a single vertical main vent through which magma reaches the earth's surface.

Volcanoes are classified into three categories based on their frequency of eruption, namely:

1. Active volcanoes: Are those that either erupt constantly or have erupted in recent times. Eg; Oldonyo Lengai.
2. Dormant volcanoes: Are those that have been inactive for some time(a few thousand years) but can erupt again. Eg; Mt Kilimanjaro.
3. Extinct volcanoes: They have not erupted in recorded history. They will probably never erupt again.

1. Landscape: Most of the earth's surface is covered with volcanic rocks. Volcanoes are also responsible for the formation of many mountains and islands.
2. Vegetation and wildlife: Volcanic eruption sometimes set the surrounding vegetation into fire. Being buried into the lava or being burnt by the forest fires also kills wild animals.
3. Environment: Volcanic eruptions emit harmful gases into the environment. Such gases include Sulphur dioxide. Some of the gases contribute to global warming and climate change.
4. Human life and property: Volcanic eruptions sometimes kill people and destroy property.
5. Soil: Volcanoes help in soil formation by bringing important minerals from deep underground onto the earth's surface.
6. Minerals: Volcanoes also bring valuable minerals to the earth's surface. The minerals are important economic resources.

An earthquake is a sudden motion or shaking of the earth caused by a sudden release of energy that has accumulated within or along the edges of the earth's tectonic plates.

Earthquakes happen when rocks in the earth's crust move suddenly, shaking the earth. Earthquake also occur because of movement of magma at constructive boundaries under volcanoes and where continental plates collide and push mountain ranges.

Earthquakes mostly occur on or near the boundaries between tectonic plates. However, earthquakes can also occur far from plate boundaries. Such earthquakes probably occur because of faults formed millions of years ago.

The point within the earth where an earthquake begins is called the hypocenter or the focus of the earthquake. Earthquake rarely occur along constructive plate boundaries.

They are grouped into three categories:

1. Primary waves or p-waves: Are the first waves released from the hypocenter. They are felt as a sudden jolt.
2. Secondary waves or s-waves: These arrive a few seconds later after p-waves. They are felt as a series of side-to-side tremors.
3. Surface waves.-They radiate outward from the point on the earth's surface directly above the hypocenter. This point is called the epicenter of the earthquake.

There are two types of surface waves:

1. Reyleigh waves- create a rolling movement that makes the land surface move up and down.
2. Love waves- make the ground shift from side to side. The surface waves damage to surface structure such as buildings and hydroelectric power plants.

The nature of an earthquake is usually described by measuring two properties, namely the magnitude and intensity.

The magnitude of an earthquake is a measure of the energy it releases. It is usually measured on the Richter scale.

The Seismograph: Is an instrument used to record ground movements caused by earthquakes. It measures ground oscillations by recording the relative motion between a pendulum and the ground.

The following are some of the hazards associated with earthquakes:

1. Landslides
2. Tsunamis
3. Collapsing buildings
4. Fire outbreak
5. Backward rivers

The following are important signs that are observed before an earthquake occurs:

1. Thermal indicator
2. Water indicator
3. Seismo electromagnetic indicator
4. Animal indicator
5. Human indicator

The following are some precautions that can be taken to minimize injuries or death of human beings in the event of an earthquake:

1. If you are indoors during an earthquake, drop, cover and hold on. Get under a desk, table or a bench. Hold on to one of the legs and cover your eyes. If there, is no desk or table nearby, sit down against an interior wall.
2. Pick a safe place where things will not fall on you-away from windows or tall heavy furniture.
3. Do not run outside when the earthquake happens because bricks, roofing and other materials may fall from buildings during and immediately after an earthquake, injuring persons near the building.
4. Wait in your safe place until the shaking stops, then check to see if you are hurt.
5. Move carefully and watch out for things that have fallen or broken creating hazards. Be ready for additional earthquakes called after shocks.
6. Be on the lookout for fires. Fire is the most common earthquake-related hazard due to damaged gas and electrical lines.