volcanoes in our community volcanic landforms and how they are made science std: geo # 3f
TRANSCRIPT
Volcanoes in our Community
Volcanic Landforms and How they are made
Science Std: Geo # 3f
When a volcano erupts…… It forms one of 2 main types of volcanic cones
A Composite Cone
A Shield Cone
And the type of cone depends on the type of lava
that the volcano makes
Types of lava?????…… The type of lava depends on what the magma is made of
Magma is a mixture of: Liquids (water) Melted Rock Dissolved Gasses
Depending on the mixture, the lava behaves differently
Types of lava?????…… The type of lava depends on what the magma is made of
Magma is mostly silicon and oxygen
1 Silicon atom combines with 4 oxygen atoms to make an “silicate ion”
These ions combine with other ions to make most of the minerals in rocks today
Types of lava?????…… The type of lava depends on what the magma is made of
The quantity (%) of silica in magma and affects how easily magma flows
We will look at 3 different silica amounts…..
Low (50%) Med (60%) High (70%)
Low Silica Magma……. Has a low viscosity (flows easily) Easily forms lava on the surface
Doesn’t erupt with a big bang
Low (50%) Med (60%) High (70%)
Oozes up for its eruption
Has to be very hot to melt Makes a lot of lava
Erupts from a single vent
So, all of these things put together make a….
A Shield Cone
The magma oozes out from the top, easily flows and spreads out making a large, flat, gently sloping volcano
It is called a shield volcano because it looks like a broad shield that used to be carried by ancient warriors
Medium Silica Magma……. Has a medium viscosity Has a harder time forming lava
Sometimes erupts with a big bang Med (60%)
Spurts for its eruption
Isn’t as hot as low silica magma
Makes less lava
Can come from more than one vent
Makes a taller volcano than low silica magma
High Silica Magma……. Has a high viscosity (hard to flow) Has a hardest time forming lava that flows Can easily erupt with a big bang
Med (60%)
Squirts like toothpaste for its eruption Can easily trap gasses in/below the magma flow
Makes the least amount of lava
Can blow out anywhere on an existing volcano
Both the Medium and the High Silica Magma have violent eruptions and can form…….
High (70%)
A Composite Volcano
The thick, stiff lava piles up and forms the tall volcanoes that we are used to see when we think of a volcano
These volcanoes have deep domes and steep sides that can be easily seen on a topographic map
A Composite Volcano
The thick, stiff lava piles up and forms the tall volcanoes that we are used to see when we think of a volcano
These volcanoes have deep domes and steep sides that can be easily seen on a topographic mapWhen the trapped gasses break free, they can be
explosive in a violent eruption that can blast pieces of lava and rock (pycroclastics) into the air
A Composite Volcano
When the trapped gasses break free, they can be explosive in a violent eruption that can blast pieces of
lava and rock (pycroclastics) into the air
A composite cone forms after many eruptions.
After each initial blast, gooey lava oozes out of the top building up the volcano.
After each eruption, the volcano goes quiet until the pressure builds up again and then……
When a large eruption happens
The edge of the old cone may fall in making a big crater called a Caldera
The caldera may be bigger than the original vent that caused it
OriginalVent
With an eruption, you can get….
Lava
Lava is the molten rock that comes out of a volcano
It is magma when it is still in the ground, lava when it comes out of the ground
Lava Flow
Lava flow is the river of lava that comes out of the volcano
It is also what you call the hard rock that is made by the lava flow once it cools off
The way the lava flows depends on a couple of different things………
The lava will flow….
Slowly if:
It has a high amount of silica in it
If it is cooled by rain or other things
Faster if:
It has a low amount of silica in it
Nothing cools it off
It is traveling down a steep slope
If it is traveling on a level ground or a small slope
The lava will flow….
If the lava starts to crust over
It can block the path of the lava for a time
It can also form a “lava pipe” or “lava tube” that can carry the lava
If the end or the side of the tube breaks open, the lava can come out and continue to flow over the ground at 10
km/hr (7 mph)
When a lava tube breaks open, it looks something like this…..
While it is traveling in the tube, it can go 45 km/hr (30 mph)
Once it starts flowing……
There isn’t much that can stop it
The largest lava flow in history was in Iceland in 1783 and it covered an area equal to 100,000 soccer fields
Other types of flows include….A Pyroclastic Flow
This is a thick mixture of hot ash, rocks and gasses that are thrown out of a volcano
with an explosive eruption
A pyroclastic flow covered Pompeii in the early 1st
century in a matter of minutes
They can move at speeds up to 350 km/hr
And it destroys just about everything in its path
Other types of flows include….
A LaharIs a mixture of water, mud, and volcanic rock fragments
It looks and acts like wet concreteHeat from the
volcano can melt snow and ice and
cause lahars to flow carrying
boulders and other large objects
Volcanic material can also dam
rivers which can break free and
flow down hill in a rapid “flash flood”
