Earthquakes and Volcanoes

VOLCANOES

VOLCANOES are places where molten rock called Magma leaks out through a hole or crack in the

                        earth’s crust.

Magma: Is the Molten rock containing liquids, crystals and dissolved gases that forms within the upper

                part of the earth’s Mantle and crust.

Note:

Volcanoes are caused by movement of molten rock and heat deep inside the earth.

Lava: Is a magma (Molten rock) that reaches the earth’s surface during a volcanic eruption.

Most of volcanoes form along constructive and destruction boundaries between tectonic plate.

VOLCANOES AT DESTRUCTIVE BOUNDARIES

When an ocean plate plunges under another plate, the ocean plate rubs the plate above it and get hot, hence rocks melts resulting in magma under the upper plate.

The Magma forces its way through weak points in the crust, hence creates lines of volcanoes called ²the ring of Fire². Eg. Ring of fire along the west coast of South America, and North America through Japan, the Philippines and New sea land.

VOLCANOES AT CONSTRUCTIVE BOUNDARIES

These are formed where two plates move a part at the boundary. Magma moves up from underneath to fill the gap left by the separating plates. The Mid – Atlantic Ocean is a continuous volcano that is thousands of kilometers long.

HOT-SPOT VOLCANOES

Are volcanoes erupted thousands of kilometers away from tectonic plate boundaries. These eruptions occur over places in the Mantle that are hotter than normal.

e.g. : Nyamulagira volcano in Congo is a hot- spot volcano.

TYPES OF VOLCANOES

         i.   Fissure volcanoes

       ii.   Central volcanoes

FISSURE VOLCANOES

These occur along cracks in and between tectonic plates.

Lava is usually affected quietly and continuously, forming enormous plain or plateaus of basaltic volcanic rock.

CENTRAL VOLCANOES

These volcanoes have a single vertical main vent through which Magma reaches the earth’s surface.

 They usually develop a cone shape that builds up from successive layers of lava and ash.

CLASSIFICATION OF VOLCANOES

Volcanoes are classified into three categories based on their frequency of eruption.

         i.  ACTIVE VOLCANOES: Are volcanoes that either erupt constantly or have erupted in recent times an example is Oldonyo lengai volcano.

       ii.   DORMANT VOLCANOES: Are those that either erupt constantly or have erupted in recent times (a few thousand years) but erupted again. An example is Mt Kilimanjaro.

     iii.    EXTINCT VOLCANOES: Are volcanoes that have not erupted in recorded history. They will probably never erupt again.

EFFECTS OF VOLCANOES

         i. Volcanoes are responsible for the formation of many mountains and Islands.

       ii.  Volcanic eruptions destroy vegetation such as forests, woodlands and grass lands.

     iii.   Volcanic eruptions cause death of wild animals

     iv.    Volcanic eruptions cause environmental pollution. Some of the harmful gases such as sulphurdioxide pollute environment.

       v.   Volcanic eruption cause killing of people and destroy property.

     vi.   Volcanic eruption help in soil formation by bringing important soil minerals from deep underground on to the earth’s surface.

    vii.   Volcanic eruption brings valuable mineral to the earth’s surface.

  viii.   Volcanic eruption helps to generate geothermal power.

EARTH QUAKES

Are saddened earth movements or vibration in the crust.

Seismology: Is the scientific study and interpretation of the earth quakes.

CAUSES OF EARTH QUAKES

         i. Earth quakes are caused by movement or sliding of tectonic plates. When tectonic plate met they cause stress and fracture of the crustal rocks, hence causes release of energy which generates shock waves which shake the earth.

       ii. Are also caused by volcanic eruption, where high pressure in the crust pushes out Magma strongly and causes vibrations.

     iii.  Also locally earth quakes may be caused by mass wasting, falling of meteors from the space, human activities.

NOTE:-

When earth quakes occur in oceans they creates oceanic waves called²Tsunami²

IMPORTANT TERMS

         i.   FOCUS

                Is the point where the earth quake originates. Sometimes called “Hypocenter”

       ii.  EPICENTER

Is the point where the shock waves (Earth quakes) hit first and give rise to an earth quake.

SEISMIC WAVES

Are waves generated by the earth quakes.

TYPES OF SEISMIC WAVES

i)    Body waves

ii)  Surface waves

BODY WAVES

Are seismic waves that travel within the earth is crust.

TYPES OF BODY WAVES

A.   PRIMARY WAVES(P-WAVES)

Are longitudinal waves that are very fast and they can travel far from interior.

PROPERTIES OF PRIMARY WAVES

i)   Are the first waves released from the focus.

ii)  They are very fast and very strong.

iii) They cause the crust to move back and forth in the direction of wave movement.

iv) They can travel through both liquid and solid matter.

v)  They are longitudinal waves. They are like sound waves.

 B.  SECONDARY WAVE(S-WAVES)

Are transverse waves that cause the crustal rock to move from side to side.

They are transverse waves. They like light waves.

  

PROPERTIES OF SECONDARY WAVES

i)  They are medium speed waves.

ii)  They affect one side of epicenter.

iii) They cause the crustal rocks to move from side to side at a right angle to the direction of wave movement.

iv) They are transverse waves. They like light waves.

v)  They cannot travel through liquid matter.

SURFACE WAVES

Are seismic waves that travel through the surface rocks.

TYPES OF SURFACE WAVES

i)  Rayleigh(R) waves

ii)  Love (L) waves

RAYLEIGH WAVES

Are surface waves that cause the surface rock to have vertical circular movements.

PROPERTIES OF RAYLEIGH WAVES

i)  They are very destructive as they occur on the surface.

ii)  Create rolling movements that makes the land surface move up and down like water waves.

LOVE WAVES (L-WAVES)

Are surface waves that cause the surface to move from side to side at a right angle to the direction of

wave movement.

PROPERTIES OF LOVE WAVES (L-WAVES)

i)  They make the ground shift side to side

ii)  They produce entirely horizontal motion

iii) It is surface waves that do damage to surface structure such as buildings and hydroelectric power plants

SEISMOGRAPH

Is an instrument used to record ground movements caused by earth quakes.