Physical Geology 101


Conical or dome-shapes landforms
Magma rises from a magma chamber through a conduit (vent)
Volcanoes are built from eruption of lava flows and deposition of pyroclastic materials
Type of volcano that develops depends on composition of lava and type of material (pyroclastic or flow)

Location of Volcanism

Where are most active volcanoes found?
Other locations?

Spatter Cones

Small cones - (only a few meters tall)
Composed of basalt
Associated with and built on top of pahoehoe lava flows
Spatter Cone Example 1
Spatter Cone Example 2

Cinder Cones

Also called Scoria Cone
Cinders (scoria of basalt or andesite) are erupted from a central vent
Loose cinders form a cone-shaped pile around the vent
Eruption crater
Lava flows
Cinder Cone Example 1
Cinder Cone Example 2
Cinder Cone Example 3
Cinder Cone Example 4
Cinder Cone Example 5
Cinder Cone Example 6

Strombolian-style Eruption

Eruption style - Strombolian - results from bursting bubbles of gas in the magma

Eruption Sequence


Shield Volcanoes

Built from pahoehoe lava flows - basalt
Shallow slopes with relatively flat tops (look like a shield lying on the ground)
Spatter Cones often develop
Summit calderas
Largest volcanoes in the world and Solar System
Shield Volcano Example 1
Shield Volcano Example 2
Shield Volcano Example 3
Shield Volcano Example 4


Also called Composite Cones
Composed of lava flows and pyroclastic deposits of andesite, dacite or rhyolite
Violent eruption - due to gas content and high viscosity magma
Ash deposits can be extensive
Stratovolcano Example 1
Stratovolcano Example 2
Stratovolcano Example 3
Stratovolcano Example 4
Stratovolcano Example 5
Stratovolcano Example 6
Stratovolcano Example 7


Lava flows of andesite, dacite, rhyolite or obsidian - viscous lava - low gas
Typically steep-sided with relatively flat tops
Endogenous domes - lava builds the dome from the inside
Exogenous domes - lava builds the dome by flows on the surface
Dome Example 1
Dome Example 2
Dome Example 3
Dome Example 4
Dome Example 5
Dome Example 6
Dome Example 7

Flood Basalt

Fissure eruptions of basalt lava flows covering 100’s to 1000’s of km2.
Flood Basalt Example 1
Flood Basalt Example 2
Flood Basalt Example 3


Collapse structures
Form due to the eruption or draining of magma from the magma chamber.
May or may not be associated with a volcanic cone.
Caldera Example 1
Caldera Example 2

Sea Floor Volcanism

Most active form of volcanism
Greatest volume of erupted material produced

Hot Springs

Hot water resulting from recent, current or impending volcanic or magmatic activity.
Magma body cooling will heat surrounding groundwater.
Minerals dissolved in hot water are deposited at surface when water cools or evaporates.

Erosion of Volcanoes

Volcanic neck - vent of a volcano remains after the cone has been eroded away
Watch a short video to see the relationship between a volcanic neck and the cone.

Dikes - conduit for lava reaching the surface - often sheet-like structures
Erosion Example 1
Erosion Example 2
Erosion Example 3
Erosion Example 4