Volcanoes.

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Lecture 29

• Volcanoes.

Chapter 14.15 ? 14.17

• Sedimentation
• Types of volcanoes and lavas
• The Rock Cycle

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Sedimentation
Materials transported by the erosion agents are
eventually deposited to form sediments.
The ultimate destination of the debris is ocean.
The material is carried toward the ocean in
stages. It can be stored on the river banks
(alluvial fans, river delta) or at places of old
glaciers (moraine). Groundwater can deposit
materials in the pore spaces of sediments, which
are eventually converted to rocks. Dissolved
materials precipitate in cracks to form
veins. Stalactites and stalagmites are examples
of groundwater depositions.
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Volcanoes
A volcano is an opening in the earths crust
through molten rock gets to the surface. The
eruption material is called magma inside and lava
outside. There are 2 types of volcanoes strato
and shield.
Character of an eruption is determined by the
viscosity of the magma and the amount of gas it
contains. The more viscous the lava, the slower
it moves. Volcanic gases include water vapor,
CO2, N2, H2, and sulfur compounds (temperature of
1000 C).
Currently there are 1500 active
volcanoes. Nearly 50 erupt every year.
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Lava
Lava solidifies into various volcanic
rocks. Types of lava pahoehoe and aa.
The most common of these rocks, basalt, has a low
viscosity. More viscous andesite produces steep,
conical mountains. Rhyolite, the most siliceous
one, produces small, thick flows and
domes. Viscous and gaseous lava may solidify in
pumice than contains many cavities and can float
in water.
Molten rock that solidifies inside crust not
reaching the surface forms intrusive bodies
(plutons). They have larger grains than volcanic
rocks on the surface, because of slower cooling
(example, granite).
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Summary
There are only 3 different types of rocks
according to their origin igneous, sedimentary,
and metamorphic. Rocks undergo a transformation
cycle between these types. The Earth is still
heated by radioactive elements which exist in its
core since the formation time. The internal
heating is responsible for Earths geological
activity, including earthquakes. Erosion is an
important process changing rocks on Earth due to
the presence of the atmosphere.