VOLCANOES

Presented by: Mrityunjay Kumar JhaPh.D. student in Geology (RGIPT)Date: 27/10/2015

Introduction

Volcano is a vent in the earth’s crust through which hot lava and volcanic gases erupts away.

magma

central vent

side vent

lava

old layers of lava

ash cloud

Earth’s crust

crater

Glossary of terms 1. Magma chamber

2. Bedrock3. Conduit (pipe)4. Base5. Sill6. Branch pipe7. Layers of ash emitted

by the volcano8. Flank9. Layers of lava emitted

by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15. Ash cloud

Types of Volcanoes

Active : Erupts very often, occur at crustal plate boundaries.

Dormant : Erupts after long interval of time.

Extinct : Which has not shown eruption since long geological history.

Cause for different types of volcano

Volcanic Products Gaseous: Steam(90%)

+CO2+N2O+SO2+H+CO+S+CL+... Liquid: Lava

Acidic Lava- More viscous, less mobile Basic Lava- Less viscous, more mobile

Solid: Pyroclasts- Solid rock fragments produced Volcanic Blocks- Bigger angular fragments Volcanic Bombs-Bigger somewhat

rounded or spindle shaped Lapilli or Cinders- Size of gravels to peas (4mm- 32 mm) Ash- Particles having size 0.25- 4.0mm Dust- Very fine particles <0.25mm

Tuff

Agglomerate/Volcanic breccia

Volcanic product’s effect

Volcanic Cones

Volcanic eruptionsEruptions- 1) Central eruptions, and 2) Fissure eruptionsFactors determining the nature of eruption- 1)Composition of magma, 2) Temperature of magma, and 3) Dissolved gases amount.

Types of volcanic eruptions Hawaiian Type- Mobile basaltic lava discharges quietly.

Ex- Hawaiian volcanoes as Mauna Loa and Kilauea Strombolian Type- Viscous lava erupts with moderate

explosion. Ex- Stromboli volcano in Sicily Vulcanian Type- More violent ejects cinders, ash and

dust. Dark clouds of dust forms. Vesuvian Type- Lava charged with gases erupts forms

a cauliflower like cloud of gases and dust at great height.

Plinian Type- Most violent, blast of up rushing gases rises to great heights.

Pelean Type- Blocked vent get cleared due to violent explosions, gases and ash spread widely.

Types of volcanic eruptions

Graph showing explosiveness and height of different types of volcanic eruptions

Surface of lavaflows

Surface texture of lava flow depending on temperature, composition and flow velocity Blocky Lava- Highly viscous, slow

moving, rhyolitic lava shows rough surface.

Ropy Lava- Smooth but twisted surface, formed due to fast flowing basaltic lava.

Pillow Lava- Basaltic lava solidifying at sea surface exhibits pillow like structure. Glassy outside, finely crystalline inside.

Identify lavaflows

Ropy Lava

Blocky Lava

Pillow Lava

Phenomena associated with voacanism Hot Springs- Surface water coming in contact

with hot rock or gases re-emerges as hot springs. Fumaroles- Steam or hot gases discharging from

vent, often deposit minerals like native sulphur, realgar and orpiment near the vent.

Geysers- Fountains of hot waters ejecting periodically may be up to height of 30-60 m.

Mud Volcanoes- A discharge of HC gases, muddy saline water and traces of Petroleum do not apparently show relation with actual volcanic activity.

Identify the phenomena?

Geysers

Hot Springs

Fumaroles

Mud Volcanoes

Volcanic Activity and Plate Tectonics Volcanic activity at spreading

centres- Basaltic magma rises from asthenosphere

Volcanic activity at Subduction Zone- Andesitic to granitic composition, violent, form island arc system.

Intraplate Volcanic activity- Difficult to explain, may be associated with initial stage spreading centres.

Volcanic Activity and Plate Tectonics

Distribution of Volcanoes

The Circum Pacific Belt (Ring of Fire) The Alpine – Indonesian belts The Mid- Oceanic Ridges African Rift valley.

Distribution of Volcanoes

Alpine- Indonesian belts

Mid- Oceanic Ridges

Circum- Pacific belt

African rift valleys

References

Principals Of Engineering Geology By K M Bangar

https://en.wikipedia.org/wiki/Volcano Various internet sources for

pictures…

Questions????????.....