This document summarizes volcanic hazards and their causes. It describes how volcanic eruptions can range from non-explosive lava emissions to extremely violent explosive bursts. The three main causes of volcanic eruptions are the buoyancy of magma, pressure from exsolved gases, and the injection of new magma. Volcanic hazards include lava flows, pyroclastic flows, ash, and gases. Primary effects are volcanic gases, lava flows, pyroclastic flows, and flooding. Earthquakes can precede and accompany eruptions, caused by displacement of lava. Most volcanic activity occurs along subduction plate boundaries like the Pacific Ring of Fire.

1. VOLCANIC HAZARDS &
BY:
THOMAS CHINNAPPAN . A ,
M.SC.APPLIEDGEOLOGY,
PERIYAR UNIVERSITY,
SALEM.
VOLCANIC ACTIVITY

2. VOLCANIC ACTIVITY ;
Volcanic activity ranges from
emission of gases, non-explosive lava
emissions to extremely violent
explosive bursts that may last many
hours.
 The types of eruptions determine the
relative volumes and types of
volcaniclastic material and lava flows,
consequently the shapes and sizes of
volcanoes.

3. CAUSES OF VOLCANIC ERUPTION ;
Although there are several factors triggering a volcanic
eruption, three predominate ways:
The buoyancy of the magma.
The pressure from the exsolved gases in the magma.
The injection of a new batch of magma into an already filled
magma chamber.

4. VOLCANIC HAZARD:
A volcanic hazard refers to any
potentially dangerous volcanic process
(e.g. lava flows, pyroclastic flows, ash).
A volcanic risk is any potential loss or
damage as a result of the volcanic
hazard that might be incurred by
persons, property, etc. or which
negatively impacts the productive
capacity/sustainability of a population.

5. PRIMARY EFFECTS OF A VOLCANIC ERUPTION:
Volcanic gases: All magma contains dissolved
gases. These gases are mainly steam, carbon
dioxide and compounds of sulphur and chlorine.

6. Lava flows:
These are streams of molten
rock.
Pyroclastic flows:
These are high speed
avalanches of hot ash, rock
fragments and gas which
move down the sides of a
volcano.

7. Flooding: Explosive eruptions can change the surface areas
around a volcano and disrupt drainage patterns, leading to
long-term flooding.

8. VOLCANIC COLLAPSE :

9. Volcanic eruptions produce
earthquakes. Earthquakes may
proceed and accompany and
frequently followed by volcanic
eruptions.
They are caused by sudden
displacement of lava within or
beneath the earth crust.

10. There are two general categories of earthquake that can occur at a
volcano ;
 Volcano-Tectonic Earthquake
Long Period Earthquake.

11. VOLCANO-TECTONIC EARTHQUAKE
A volcano tectonic earthquake is
caused by the movement of magma
beneath the surface of the earth.
The movement results in pressure
changes where the rock around the
magma has experienced stress.
At some point, this stress can
cause the rock to break or move.

12. LONG PERIOD EARTHQUAKES ;
These earthquakes are a result of pressure changes during the
unsteady transport of the magma.
When magma injection is sustained a lot of earthquakes are
produced. This type of activity indicates that a volcano is about
to erupt.
Scientists use seismographs to record the signal from these
earthquakes. This signal is known as volcanic tremor.

13. VOLCANOES ALONG SUBDUCTION PLATE
BOUNDARY ;
So, volcanic activity tends to occur along subduction plate
boundaries, where one plate slides underneath another.
The edges of the Pacific Plate make up a long subduction
boundary. There are a huge number of earthquakes along these
boundaries, because these are regions where the plates are
colliding.
For the same reason, the majority of the volcanic activity on the
Earth also occurs along these convergent boundaries. This is
called the Pacific Ring of Fire where over 75% of the world’s
volcanoes are found.

14. PACIFIC RING OF FIRE :

15. CONCLUSION
Though volcanic eruptions are threats to human life, the areas
where the eruptions have taken place are useful too. They have
helped to create beautiful Hawaiian Islands.
These areas are rich in minerals.
(Most of the metallic minerals mined in the world--such as
copper, gold, silver, lead, and zinc--are associated with magmas
found deep within the roots of extinct volcanoes.)
 Volcanic materials ultimately break down and weather to
form some of the most fertile soils on Earth.

16. THANK YOU