Volcanic bombs are fragments of new magma ejected from a volcano
during an explosive eruption. Blocks are chunks of pre-existing
rock torn from the interior of the volcano during eruptions.
Together they constitute ballistic ejecta. Both are locally
destructive and can kill.
Bombs and blocks can travel with velocities of hundreds of kilometres
an hour.
They can reach heights of several kilometres above the volcano.
Bombs and blocks 1 - 2 m (3 - 6 ft) across can be thrown 3 -
5 km (2 -3 miles) from the vent.
They can carry sufficient energy to penetrate most structures.
They may be hot enough to start fires.
Fig 5. Volcanic bombs & associated damage
Associated terms:
Debris flows
Mudflows
Lahars are dense flows of water mixed with volcanic ash and
boulders. On erupting Caribbean volcanoes, they typically occur
after periods of intense rainfall. Although they look like mud,
they often behave like floods of water. They can be deadly and
severely damaging to property and lifelines. They can also clog
river channels leading to serious flooding.
Lahars are topographically controlled and follow valleys and
depressions. |
Velocities vary according to density, but can reach 100 km/h
(60 mph).
They can travel for several kilometres and, even on the larger
volcanic islands of the Caribbean, may reach the sea.
They may be hot or cold, according to the proportion of hot
volcanic material they contain.
Fig 6. Lahar deposits (Montserrat)
Associated terms:
Hydromagmatic eruptions/explosions
Vulcanian eruptions/explosions
Phreato-magmatic eruptions are violent explosions involving
both magma and water. Ash and blocks can be hurled long distances
from the volcano. The boulders can be lethal and damaging
over a wide area.
Blocks may be either fragments of new magma (bombs) or chunks
of older rock torn from within the volcano.
Velocities may reach hundreds of kilometres an hour.
Blocks of lethal size (5 cm or 2 inches) can reach distances
of 20 km (12 miles).
Most serious damage occurs within 5 km (3 miles) of the vent.
Eruptions are loud and may be accompanied by thunder and lightning.
The resulting large ash clouds can reach altitudes of several
kilometres.
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