Introduction

• Volcano, mountain or hill formed by the accumulation of materials erupted through one or more openings (called volcanic vents) in the earth's surface.

• They are usually found along diverging plate or constructive plate.

Introduction

• Volcanoes are active, dormant or extinct.

• There are 3 types of volcanoes: composite, cinder and shield.

– Lava Basic or acidic lava– Gas Carbon Dioxide, Sulphur dioxide

– Pyroclasts Ash, dust, volcanic bombs

Eruptive Styles

Composition • Silica Content- Amount of SiO2 that lava contains

– The higher the amount of SiO2 the more explosive the eruption

• Gas & Water Content-Amount of volatiles (C02, Water, Sulfur, etc) – The higher the amount of volatiles dissolved in magma the more

explosive the eruption

ViscosityMeasure of how easily material can flow; Low viscosity, lava

flows easily; high viscosity, it does not; The more viscous the lava the more explosive the eruption

LavaType Acid Lava Basic Lava

Production Subduction Constructive Plate

Content Rich in silica Rich in iron and magnesium

Temperature 8000C 12000C

Type Viscous Fluid

Movement Slowly Quickly

Time taken to cool

Cools, solidifies quickly

Cools, solidifies slowly

Distance Does not flow far Flows very far

Explosion Violent Quiet

Structure of a volcano

                                                                                                                                                             

Formation of Volcano

• Formed along along diverging plate or constructive plate.

• Magma rises from the mantle through fractures due to the immense gas pressure in the magma chamber.

• Volcanic material spills or shots out from the vent and piles up on the ground around the vent.

• Forms a volcano.• Volcano can be formed through hot spots.

Composite Volcano

• Alternate layers of pyroclasts• Steep slopes and gentle base due to larger

pyroclasts fall near the summit while the finer pyroclasts fall near the base

• Acid lava solidifies in the central pipe build up tremendous pressure loud explosions

• Examples: Mt Merapi, Mt Mayon, Mt Fuji, Mt St Helens

• Also known as StratoVolcano

Mt St HelensMt St Helens

Ash and Cinder Volcano

• Steep sided symmetrical volcano form from red-hot cinders and ash.

• Steep slopes and gentle base due to larger pyroclasts fall near the summit while the finer pyroclasts fall near the base

• Bowl-shaped summit crater

• Grows rapidly and found in groups

• Examples: Paricutin

Paricutin, Mexico

Shield Volcano

• Slightly domed shaped volcano

• Fluid basic lava

• Wide base

• Not explosive

• Little pyroclasts

• Example: Mauna Loa that is formed form hot spot

Hot Spots

• Rising columns of or plumes of magma that originate form a fixed position

• Magma plume melts a hole in the lithospheric plate

• Magma issues out from the vent

• As plates move, the volcano becomes extinct and anew volcano is formed

• The further the volcano is from the hot spot, the older it is.

A field of lava from Mauna Loa that has hardened into smooth, folded sheets of rock

Eruption of Kilauea crater spilled molten lava down the flanks of Mauna Loa volcano in Hawaii Volcanoes National Park

Gentle slope of Mauna Loa