Transcript Volcanoes and Magma

Volcanoes and Magma
Julie, Liz and Tyler
Volcanic eruptions occur only in certain
places… they do not occur randomly
ONE WAY THEY OCCUR…
Plates colliding…
• The Earth's outermost shell  the lithosphere is broken
into a series of slabs known as lithospheric or tectonic
plates.
– These plates are rigid, and they float on the hotter,
softer layer in the Earth's mantle. As the plates move
about, they spread apart, collide, or slide past each
other.
= A Volcano occurs most frequently at
plate boundaries… when plates collide
together!
Land and underwater volcanoes…
Mount St. Helens is typical of more than 80 % of the
volcanoes that have formed on land.
Submarine or underwater volcanoes usually originate
rear the Mid-Oceanic Ridge system
*Known as subduction zone volcanoes, they occur along
the edges of continents where one plate dives, or
subducts, beneath a second plate.
*Western Washington and Oregon are near a subduction
zone and in a region likely to experience future volcanic
activity. Kansas and Nebraska are not.
Another way volcanoes
occur…
Hot spots…
• Some volcanoes occur in the interior of plates at areas
called hot spots, are caused by upwelling of deep
mantle plumes.
-Hawaii is the best known example of hot spot
volcanism!
**Other examples of hot spot volcanoes are located in …
Iceland
Piton de la Fournaise
Canary Islands
Heard Island
McDonald Island
Intrusive Igneous Rocks (Plutonic
Rocks):
Plutonic rocks (also called intrusive igneous rocks ) are
those that have solidified below ground. When magmas
crystallize deep underground they look different from
volcanic rocks because they cool more slowly and,
therefore, have larger crystals. Igneous rocks cooled
beneath the Earth's surface are called intrusive rocks.
Intrusive Igneous Rocks:
Intrusive, or plutonic igneous rock forms when magma is
trapped deep inside the Earth. Great globs of molten
rock rise toward the surface. Some of the magma may
feed volcanoes on the Earth's surface, but most remains
trapped below, where it cools very slowly over many
thousands or millions of years until it solidifies. Slow
cooling means the individual mineral grains have a very
long time to grow, so they grow to a relatively large size.
Intrusive rocks have a coarse grained texture.
The three things that create magma…
• increase in temperature in the asthenosphere
• decrease in pressure ~ pressure-release meltingmelting is caused by decrease in pressure
• additional water, a wet rock melts at a lower
temperature than an identical rock that is not wet.
Intrusive Igneous Rock…
• Pluton – in the Earth’s crust granitic magma solidifies
and granite is formed in a large mass.
• Granitic magma is formed near the base of the crust and
is surrounded by hot plastic rock. Magma then rises.
The plastic rock fills back in behind it.
– batholith – is exposed on the earth’s surface for more than 100
square kilometers. Is made up of many smaller plutons that rise
sequentially over time
– stock – less than 100 kilometers is exposed on the earth’s
surface
– dike – sheet like, forms when magma slides into a fracture
– still – sheet like rock parallel to layering, forms the same way as
dikes do
Group 3 ROCKS…get it???