Physical Geography 102
Volcanic Landforms I


Land forms are surface features of the land
geo- =
morph- =
-logy =
Landforms are defined in terms of its shape, but are controlled by the composition of the earth materials

Landform Formation

Landforms are created by two forces
Internal Forces - build up new features by moving crustal material
Volcanic activity
Plate Tectonics

Landform Formation

External Forces - act upon crustal material - break it down and wear it away
Flowing Water
Chemical Reactions

Volcanic Materials

Landforms which develop from the eruption of magma and are built of volcanic materials

Volcanic Materials

Volcanic landforms include more than just volcanoes
Volcanic materials can be divided into two main categories
Pyroclastic material
Flow material

Pyroclastic Material

Pyroclasts (tephra) are fragments of lava generally produced during violent, explosive eruptions
Tephra is classified by size
Ash =
Lapilli =
Bombs/Blocks =

Pyroclastic Deposits

Pyroclastic deposits - welded, cemented or unconsolidated pyroclasts
Tuff, ignimbrite, ash fall, ash flow deposits are all terms used to describe pyroclastic deposits
Lahars and Mudflows are also pyroclastic deposits, but involve water

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 _______________ of the lava

Lava Flow Types

Pahoehoe - very fluid flows - low viscosity; ropey appearance to the surface; basalt
Pahoehoe Example 1
Pahoehoe Example 2
Pahoehoe Example 3
Pahoehoe Example 4

Aa - higher viscosity than pahoehoe; surface consists of spiny, angular clinkers; basalt, andesite
Aa Example 1

Block flows - surface consists of angular blocks; andesite, rhyolite, obsidian
Block flow Example 1
Block flow Example 2


Volcanoes are built from the eruption of lava flows and the deposition of pyroclastic materials
The type of volcano that develops depends on the composition of the lava and the type of material (pyroclasts or flow)