Oh the pressure!
Deep within the
Earth, rock exists
as a hot liquid
This magma is
found in pockets
A volcanic eruption begins when this
underground molten rock builds up pressure.
When under great
pressure magma can
hold many dissolved
As the magma rises
through the rock layers, the pressure
Since the pressure of the magma is
decreasing, the gases in the magma escape
in an explosive blast at the surface.
When magma reaches
the surface it is called
The place where lava
erupts is called a vent.
Some volcanoes have
more than one vent.
Not all volcanic eruptions are alike. If the
magma is thin and fluid, there is
usually a quiet eruption.
Magma rich in silica tends to be thick. This
type of magma tends to trap water vapor, so
therefore the eruptions tend to be very
Mt. St. Helens
Types of eruptions (we’re going over 6-
there are many more)
towering ash plumes serious damage
fast moving lava
not very destructive or explosive
sluggish low gas lava flows
eruptions not dangerous
no lava flows (usually)
produce ashy tephra
Vulcanian Types of eruptions
many short explosions eruptions initiated
by high gas magma, can launch football sized pyroclasts,
generally not associated with a lava flow.
hot magma heats water
to produce steam, can melt
snow causing mudslides and Fissure
major flooding occurs when magma flows up
if it occurs through cracks and leaks out onto
undersea- the surface, characterized by curtain
Highly of fire, can produce slow moving,
explosive heavy flows
Other eruption types of note….
Vesuvian-lots of ash-laden gas
Phreatic-steam blast eruption; driven by explosive
expanding steam-no new magma-just solid rock
Pelean (or nuee ardente)-large amount of
gas, dust, ash and incandesent lava pieces,
roll down the flanks at speeds as great
as 100 mph.
Magma can sometimes
be so thick that it can
clog up a vent.
This causes the pressure
underneath to increase
leading to a more
Explosive Eruption Demonstration
baking soda dish soap
Alka seltzer vinegar
red food coloring cork
small soda bottle goggles
1. Place dry ingredients in bottle. Add the dish
soap and food coloring to this mixture.
2. Put on safety goggles.
3. Quickly pour vinegar in and immediately put
the cork into the bottle opening. Stand back!
Volcanic eruptions assignments
You will have 2 days to complete these
1. Volcanic eruptions webquest (websites
under activity information and worksheet under
documents on teacherweb page)
2. volcano paper model and questions (done
in lab notebook)
3. volcano poem and artwork (write and