Volcanic Landforms: Extrusive Igneous
Volcanic processes are constantly changing the Earth. Eruptions can create new islands.
build and destroy mountains, and alter landscapes.
Active, dormant, and ancient remnants of eruptions are all contained within our National Parks.
Types of Volcanoes
Shield volcanoes- Volcanoes ranging in size from small to truly massive, created by steady, non-violent outpouring of lava.
Mauna Loa and Mauna Kea in Hawaii are shield volcanoes rising nearly 9 km (5.6 mi) from the seafloor.
. Mount St. Helens and Mount Rainier are stratovolcanoes.
Cinder cones- Short, steep volcanoes associated with limited eruptive events.
Sunset Crater Volcano and Capulin Volcano are cinder cones.
Lava Domes-Lava domes form where thick (viscous) magma erupts to the surface forming a steep dome-shaped landform.
Lava domes can form within a crater of large composite volcano.
Maar-Diatreme Volcanoes
–maar-diatreme volcanoes are formed.
by the explosive result of subsurface magma coming into contact with shallow ground water.
The maar is the crater landform produced by explosive eruption(s) and the diatreme is the below surface rock filled volcanic pipe or conduit.
Conical Vent and Fissure Vent
Fissure vent
A fissure vent (volcanic fissure) is a narrow, linear volcanic vent through which lava erupts, usually without any explosive activity.
The vent is often a few meters wide and may be many kilometres long.
Fissure vents are common in basaltic volcanism (shield type volcanoes).
Conical vent
A conical vent is a narrow cylindrical vent through which magma flows out violently.
Conical vents are common in andesitic volcanism (composite or stratovolcano).
Mid-Ocean Ridges
The central portion of the mid-ocean ridges experiences frequent eruptions.
Composite Type Volcanic Landforms
They are conical or central type volcanic landforms.
Along with andesitic lava, large quantities of pyroclastic material and ashes find their way to the surface.
Andesitic lava along with pyroclastic material accumulates in the vicinity of the vent openings leading to the formation of layers,
and this makes the mounts appear as a composite volcano or a stratovolcano (divided into layers).
The highest and most common volcanoes have composite cones.
Mount Stromboli (the Lighthouse of the Mediterranean).
Mount Vesuvius, Mount Fuji are examples.
Shield Type Volcanic Landforms
The Hawaiian volcanoes are the most familiar examples.
These volcanoes are mostly made up of basaltic lava (very fluid).
These volcanoes are not steep.
They become explosive if somehow water gets into the vent;
Example: Hawaiian volcanoes Mauna Loa (active shield volcano) and Mauna Kea (dormant shield volcano).
Fissure Type Flood Basalt Landforms (Lava Plateaus)
Sometimes, a very thin magma escapes through cracks and fissures in the earth’s surface .
and flows after intervals for a long time, spreading over a vast area.
Example: Siberian Traps, Deccan Traps, Snake Basin, Icelandic Shield, Canadian Shield.
Crater
A crater is an inverted cone-shaped vent through which the magma flows out.
Caldera
In some volcanoes, the magma chamber below the surface may be emptied after volcanic eruptions.
The volcanic material above the chamber collapses into the empty magma chamber.
and the collapsed surface appears like a large cauldron-like hollow (tub shaped) called the caldera.
Lava Dome
A lava dome (volcanic dome) is a mound-shaped protrusion.
(a structure that extends outside the surface) resulting from the slow extrusion.
(coming out) of viscous lava from a volcano.
In Lava domes, viscous magma piles up around the vent.
Pseudo volcanic features
Salt extrusions may take the form of salt hills which exhibit volcanic crater like features.
Salt structures are impermeable and can lead to the formation of a stratigraphic trap.
(an impermeable layer capable of retaining hydrocarbons.