VOLCANISM

By Hashim Ali (7A)

What is volcanism?

• When hot molten magma escapes from the Earth’s core becoming cooler, and forming hard rocks, we refer to this process as volcanism.

Types of Volcanism….!1. Underwater Volcanism

• Underwater volcanism takes place at the constructive plate boundary on the ocean floor.

• At these boundaries, oceanic plates that diverge leave a gap between the plates from where magma from the mantle comes to the surface.

Types of Volcanism….!2. Volcanism at Destructive plate

Boundary• This takes place when an oceanic plate subducts beneath a continental

plate to melt into the mantle.• At the same zone, magma may erupt as lava.• These kind of repeated eruptions build up layers upon layers of volcanic

materials to form a volcano.

Types of Volcanism…!3. Volcanism at Hot Spots

• This takes place when columns of molten magma in the mantle rises from the hot spot to the Earth’s surface.

• It melts the crustal plate directly above it.• These columns of magma are found is fixed locations deep within the

mantle.• This is called a hot spot volcano.

Parts of a volcano

• Vent: The opening or a hole through which magma comes to the surface.• Cone: The layers of volcanic materials that build up around the vent to form a

cone-shaped structure.• Pipe: The passageway which joins the vent to the crater of the volcano.• Crater: The top of the pipe through which magma is forced onto the Earth’s

surface.• Lava: The magma which is forced onto the Earth’s surface.• Magma chamber: The cavity in the Earth’s crust below the vent that holds magma.

Parts of a volcano

Classifying Volcanoes…

• 1. ACID LAVA VOLCANO:

• It is viscous as it contains a high amount of silica.

• It flows slowly as it is highly vicous,• The eruption is usually violent and loud.

Classifying Volcanoes…

• 2. BASIC LAVA VOLCANO

• Contains high amounts of iron and magnesium.

• It is less viscous than acid lava.• Flows more quickly and over longer

distances before it solidifies.• The eruption is usually quiet.

Classifying Volcanoes…

• 3. Composite Lava Volcano

• Also known as ash and cinder volcano.• Eruptions are usually violent and loud.• They contain viscous acid lava.

Volcanoes in Pakistan!

• The mainly found volcanoes here are mud volcanoes.• They are generally passive, emitting gases that bubble passively in their craters.• Balochistan has more than 80 active mud volcanoes.

Risks and benefits for staying near or on volcanoes.

RISKS

BENEFITS

• Falling rocks, volcanic bombs and projectiles, ash and cinders at the time of eruption.

• Fertile soils from weathered volcanic rocks… helps in cultivation of food crops to feed the people.

• Hot lava from the volcanoes flow down the slopes at high speed, destroying homes, damaging infrastructure, killing people.

• Geothermal energy produced from the heat generated by volcanoes.

• Air pollution due to the enormous amount of poisonous gases which get ejected during an eruption.

• Precious minerals such as gold and silver can be mined.

• Landslides along the slopes of the volcanoes bury and destroy everything in their path.

• Scenic sights of volcanoes may attract tourists to the area.