2. • natural disaster, any calamitous occurrence generated by the effects of natural, rather than human-
driven, phenomena that produces great loss of human life or destruction of the natural environment,
private property, or public infrastructure.
• A natural disaster may be caused by weather and climate events or by earthquakes, landslides, and
other occurrences that originate at Earth’s surface or within the planet itself. No spot on Earth is
immune from a natural disaster; however, certain types of disasters are often limited to or occur more
frequently in specific geographic regions.
Introduction
3. • The Primary causes of natural disasters are often beyond human control. Risks originate
from people's exposure and vulnerability to risks caused by natural events.
• The probability of occurrence of the causing natural events must be forecasted as precisely
and as far in advance as feasible before risk mitigation measures may be implemented.
• The purpose of preventive actions must be to limit the susceptibility and exposure of
potentially affected areas.
• Natural disasters with catastrophic potential have a low likelihood of occurrence. It is
intuitively stated as a recurrence interval (in years).
Introduction
4. • A volcano is a hole in the earth's surface through which
magma (hot liquid and semi-liquid rock), volcanic ash, and
gases can escape.
• They are most commonly seen where tectonic plates collide
or separate, although they can also exist in the midst of
plates as a result of volcanic hotspots.
Volcanic Eruptions
5. • A volcanic eruption is when gas and/or lava are released from a volcano—sometimes
explosively.
• Volcanoes provide a number of environmental benefits, for example: fertile soils,
hydrothermal energy, and precious minerals.
• But they also pose several hazards: volcanic ash, gases, lahars (mud flows),
landslides, lava flows, and pyroclastic flows (fast-moving currents of hot gas).
• Volcanic eruptions can be deadly and often cause population displacement and food
shortages.
Volcanic Eruptions
6. • Volcanic eruptions have captured the imagination of people over millennia, and they
feature in several mythologies as well as works of fiction.
• These eruptions also play a role in climate change, with expelled gases such as
carbon dioxide contributing to global warming, while ash, dust, and gases such as
sulfur dioxide can drive global temperatures down.
Volcanic Eruptions
7. • Volcanic eruptions occur as a result of heat moving under Earth’s surface. They
often begin with an accumulation of gas-rich magma (molten underground rock) in
reservoirs near Earth’s surface, though they may be preceded by emissions of
steam and gas from small vents in the ground.
• Small earthquakes, which may be caused by a rising plug of dense, viscous
magma oscillating against a sheath of more permeable magma, may also signal
volcanic eruptions, especially explosive ones.
How volcanoes erupt
8. • In some cases, magma rises in conduits to the surface as a thin and fluid lava,
either flowing out continuously or shooting straight up in glowing fountains or
curtains.
• The eruptions of Hawaii’s volcanoes fall into this category. In other cases,
entrapped gases tear the magma into shreds and hurl viscous clots of lava into the
air.
• In more violent eruptions, the magma conduit is hollowed out by an explosive blast,
and solid fragments are ejected in a great cloud of ash-laden gas that rises tens of
thousands of metres into the air.
How volcanoes erupt
9. • An example of this phenomenon is the 1980 eruption of Mount Saint Helens. Many
explosive eruptions are accompanied by a pyroclastic flow, a fluidized mixture of
hot gas and incandescent particles that sweeps down a volcano’s flanks,
incinerating everything in its path.
• If the expelled ash or gases collect on a high snowfield or glacier, they may melt
large quantities of ice, and the result can be a disastrous flood or landslide that
rushes down a volcano’s slopes.
How volcanoes erupt
10. • Volcanic eruptions can also result in secondary damage, beyond the direct loss to
life and property from the eruption itself.
• Volcanic ash can cause respiratory illnesses such as silicosis and can be
particularly harmful to infants and people with chronic lung diseases. Gases such
as hydrogen chloride, carbon monoxide, and hydrogen fluoride can cause both
short- and long-term problems.
• Eruptions can cause economic harm that affects workers’ livelihoods and can force
mass migrations of people in affected regions.
How volcanoes erupt
11. • Volcanoes emit a variety of products which may be harmful to human and animal
health. Some cause traumatic injury or death and others may trigger diseases,
particularly in the respiratory and cardiovascular systems, or mental health
problems.
• 1)Mechanical injury where the body is crushed. Explosive eruptions may produce
large volumes of fragmented rock, which range in size from boulders to fine ash.
• 2)Thermal injury (burns) caused by hot volcanic emissions. These take the form of
pyroclastic density currents and surges (composed of searing gas, ash and rocks).
The impact of volcanoes on the population and public health:
12. • Diseases caused by volcanoes:
• 1) conjunctivitis.
• 2) acute and chronic respiratory diseases
from falling ash and breathing gases and
fumes.
• 3) burns and traumatic injuries, such as
lacerations from falling rock. eye and skin
irritations from acid rain.
The impact of volcanoes on the population and public health:
13. • The most fundamental way to characterize a volcanic eruption is whether it is
magmatic, phreatic, or phreatomagmatic.
Eruption Types
14. • The most fundamental way to characterize a volcanic eruption is whether it is
magmatic, phreatic, or phreatomagmatic.
Eruption Types
