Physical Science 101
Volcanic Rocks

Volcanic Landforms

Landforms which develop from eruption of magma and are built of volcanic materials.
Volcanic Materials:

Pyroclastic Material

Pyroclasts (tephra) are fragments of lava generally produced during violent, explosive eruptions
Tephra is classified by size:
Ash = <2mm
Lapilli = 2-64 mm
bombs/blocks = >64 mm

Pyroclastic Deposits

Pyroclastic deposits - unconsolidated pyroclasts, cemented or welded,
Ash Fall, Ash Flow deposits are all terms used to describe pyroclastic deposits
Lahars and Mudflows (Example 1, Example 2)

Lava Flows

Non-violent, effusive eruptions of lava which flows along the surface
Basalt is the most common lava rock type
The type of flow is controlled by the silica composition of the lava

Lava Flow Types

Pahoehoe - very fluid flows - low viscosity; ropy surface appearance; basalt.
Aa - higher viscosity than pahoehoe; surface consists of spiny, angular clinkers; basalt, andesite.
Block flows - surface consists of angular blocks; andesite, rhyolite, obsidian
Pillow lava: