This document provides an overview of volcanism, including definitions of key terms like volcano and volcanic eruption. It describes the three main types of volcanoes as composite volcanoes, cinder cone volcanoes, and shield volcanoes. The document also discusses the origin and structure of volcanoes, explaining that magma and gases cause eruptions. It outlines the three categories of volcanoes based on eruption frequency and gives examples. Areas of common volcanism are identified as subducting plate boundaries and mid-ocean ridges.

1. Volcanism
Md. Wabidur Rahman
Roll no:- 18glm044
Year:- 1st
Session:- 2017-18
Dept.of Geology and Mining
University of Barisal

2. INTRODUCTION
 What Is a Volcano?
A volcano is an opening on the surface of a planet or moon that allows material
warmer than its surroundings to escape from its interior.
 What is a volcanic eruption?
A volcanic eruption is an event in which material from a volcano,usually molten
rock and gas, are ejected onto the surface.Eruptions can range from fairly gentle
outpourings of lava toenormous explosions that sent ash and rock miles into the
sky.
 It is primarily divided into three categories by their
frequency of eruption such as:
 Active- erupts regularly.
 Inactive- erupted in historical times but are now quiet. For example-
Yellowstone, Toba, Visuvias etc.
 Extinct- unlikely to erupt again and has no longer magma supply. For
example- Hohentwiel, Shiprock and the Zuidwal volcano.

3. ORIGIN AND STRUCTURE OF
VOLCANO
ORIGION:
 The roman god Vulcan, god of forging and fire, did all of his forging of metals and such
in a volcano. the people of Rome called where he worked a vulcanas and it was
eventually changed to volcano .
 "Volcano" is derived from the name of the Island of Vulcano, which got its name from
the Roman god of fire, Vulcan.
 STRUCTURE:
 Magma – the molten, or liquid-like, rock within the Earth
 Lava – magma that reaches Earth’s surface
 Vent – an opening through which molten (liquid-like) rock flows onto Earth’s surface
What Causes Volcanoes to Erupt?
 A volcanic eruption is caused by the injection of magma into a full magma chamber,
the buoyancy of magma and the pressure exerted by the gases in the magma.

4. TYPES OF VOLCANISM
 The three main types of volcanoes are:
1. composite volcano
 Both pyroclastic layers and lava flows
 Steep sided near summit with decreasing slope
2. cinder cone volcano
 Ash and debris accumulates around the vent
 Small steep sided cones
3. shield volcano
 Has a low rounded profile
 Gentle slopes of 2-10 degrees

5. Areas of Volcanism
 Sub-ducting Boundaries
 Plate Sub-ducts below surface into mantle
 Oceanic-Oceanic
 Volcanoes form near boundary
 Mid Ocean Ridges
 Eruptions occur where plates are diverging