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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????????.....
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