 |
Emi Koussi, a Pyroclastic shield volcano,
seen from International Space Station,
Tibesti Mountain in the Central Shahara,
Northern Chad |
In
volcanology, a
pyroclastic shield or
terrestrial ignimbrite shield is an uncommon type of
shield volcano. Unlike most shield volcanoes, pyroclastic shields are formed mostly of
pyroclastic and highly
explosive eruptions rather than relatively fluid
basaltic lava issuing from vents or
fissures on the surface of the volcano. They typically display low-angle flank slopes and have little or no central collapse, although a shallow sag in the shield is commonly observed. Lava is commonly extruded after the cessation of explosive activity commonly superposes the vent region. The paucity of associated
Plinian fall deposits indicates that pyroclastic shields are characterized by low Plinian columns.
Pyroclastic shields are commonly known to form in the
Central Andes of
South America, as well as in
Melanesia (the island of
Bougainville alone has two). There are also pyroclastic shields in
Africa, such as
Emi Koussi in
Chad.
 |
Billy Mitchell, a Pyroclastic shield volcano located in
Papua New Guinea |
