Volcanic eruptions produce a wide range of hazards that threaten human populations and infrastructure. These hazards include pyroclastic flows, lava flows, landslides, flooding, ashfall, gas emissions, and tsunamis. The risks posed by these hazards depend on both the vulnerability of human settlements located near volcanoes and the types of volcanic activity, which vary based on a volcano's composition and eruptive behavior. Human activities like population growth can also increase vulnerability to volcanic hazards by exposing more people to risk. The combination of volcanic phenomena and human vulnerability is what ultimately determines the hazards posed in any given eruption.

1. Volcanic Hazards
A2 Geography

2. Objectives
• To explain why such a wide range of
volcanic hazards exist.

3. The Easy Bit
• Definitions
• VOLCANO – Main landform comprising of
surface accumulations of rock and debris
developed from the molten rock (Magma)
• ERUPTIONS – The main events
associated with rising magma. This leads
to the discharge of hot water, outpouring of
lavas, explosive gas and debris, torrential
rain, flooding, landslides and earthquakes

4. Threats to Humans
• Risk equation.
• As we settle in more vulnerable places the
more vulnerable we become to hazards.
• Our VULNERABILI|TY is often dictated by
our ability to COPE with the hazard.
• Our exposure to the hazard becomes the
RISK we face.

5. Key Point
• It is the combination of human values and
vulnerability that converts volcanic
phenomena into hazards.

6. Types of volcanic activity
• Primary - Determined by eruptive
behaviour
• Ejected pyroclastic material
• Pyroclastic flows
• Lava flows
Pyroclastic flows Lava flows
Mixture of Ash, rock and Magma that’s lost its
gas volatiles
Can travel upto 100km/h for Damages property but
70km moves much more slowly
300 – 370 C Cools quickly

7. Geology
• Chemical composition can determine lava
type:
• Iron rich, silica poor are basaltic – have
low viscosity so flow quickly and cool
slowly
• Silica rich, iron poor – Andesitic lavas are
Rhyolitic, viscous and cool quickly
BASALTIC = flow quickly cool slowly
ANDESITIC = viscous, flow slower and cool quicker

8. Secondary Hazards
• Generated by the eruption:
• Clouds form of ash, rainfall and thunderstorms develop
– flooding and landslides, often high sediment loads in
flood water. (Mudflows)
• Lahars are like flood water but consists mainly of mud
and debris and have the consistency of wet concrete
speeds can reach 40m/sec and flow for 300km
• Can carry large boulders
• Dries like very hard rock

9. Eruption induced Melting of ice
caps
• Can result in major flooding
• Particularly associated with Iceland
• Melting of ice cap on the Nevado del Ruiz
volcano, Columbia in 1985 caused
mudfloods killing 23,000 people

10. Tsunami Generation
• Discharges of oceanic volcanoes can
cause tsunami waves which can engulf
coastal areas Krakatau (1883) caused
35m high waves killing 36,000 people on
nearby islands

11. Other Hazards
• Gas Discharges – pose little danger
except for explosions.
• CO2 can be released and can, since
heavier than air be released from waters
causing it to hug the ground and cause
death to nearby inhabitants

12. Doming
• Upward movement of magma used to
forecast eruptions.
• Pronounced upward movement of land
caused over 400,000 people to be
evacuated and 100,000 permanently
rehoused near Naples Italy during the
1980’s

13. KEY POINT
• The combination of hazards varies
between volcanoes as well as within each
eruption

14. What are the Global Significance
of Volcanic Hazards
• Discuss
• Homework
• Discuss the degree to which the theory of plate
tectonics is supported by the distribution of volcanic
and seismic activity across the globe
• Marked out of 40
• Typed with front sheet
• Full bibliography