1) Volcanoes form at boundaries where tectonic plates meet, such as where plates are subducting or spreading apart. 2) There are two main types of volcanoes - cone-shaped volcanoes which form from thick, slow-moving lava and shield volcanoes which have flatter slopes due to more fluid lava. 3) Examples of highly active volcanic regions include the Pacific Ring of Fire and areas around Alaska, Hawaii, and the Cascade Range in the western United States.

1. YEAR 10 GEOGRAPHY
PLATE TECTONICS
2. VOLCANIC
ACTIVITY

2. A volcano is a spot in Earth’s crust where molten rock,
volcanic ash and certain types of gases escape from an
underground chamber.
Magma is the name for that molten rock when it’s below
ground.
Scientists call it lava once that liquid rock erupts from the
ground — and may start flowing across Earth’s surface.
(It’s still “lava” even after it’s cooled and solidified.)

4. Volcanoes take place at destructive plate boundaries and
constructive plate boundaries.
1,500 active volcanoes exist across our planet, according to
scientists at the U.S. Geological Survey (USGS).
About 500 volcanoes have erupted since humans have been
keeping records.
Of all volcanoes that have erupted in the past 10,000 years,
10% reside in the United States.
Most of them exist in Alaska (Aleutian Island chain), in
Hawaii and in the Cascade Range of the Pacific Northwest.

5. Many of the world’s volcanoes are located around the edge of the Pacific
Ocean in an arc known as the “Ring Of Fire” (shown as deep orange band).

6. Volcanoes can form on land or below the sea.
Earth’s biggest volcano lies submerged a mile below the
ocean’s surface.
Certain spots on our planet’s surface are especially
susceptible to volcano formation.
Most volcanoes form at or near the edges (or boundaries) of
Earth’s tectonic plates.
Their movement is driven largely by the circulation of the
scalding, liquid rock in Earth’s mantle.
That mantle is thousands of kilometers thick. It lies between
our planet’s outer crust and its molten outer core.

8. The edge of one tectonic plate may begin sliding beneath a
neighbouring one.
This process is known as subduction.
The downward-moving plate carries rock back toward the
mantle, where temperatures and pressures are very high.
This disappearing, water-filled rock melts easily.
Because the liquid rock is lighter than the surrounding
material, it will try to float back up toward Earth’s surface.
When it finds a weak spot, it breaks through.
This creates a new volcano.

10. The two main types of volcano are cone-shaped volcano and
shield volcano.

11. A cone-shaped volcano forms because the lava and ash
moves slowly and hardens quickly due to its thick
composition.
Any lava or ash which follows will form on the old flow,
producing a cone-shaped volcano over time.
Cone-shaped volcanoes occur at destructive plate
boundaries.

13. There are two types of cone-shaped volcanoes.
Ash and cinder cones. These cones are relatively small. Very
little lava flows out of the steep-sided cone. Instead,
fragments of lava explode out of it, solidifying in mid-air.
Examples: Mt Pelee in Martinique, Vesuvius in Italy.
Composite cones. The lava is acid in nature and is very
viscous (sticky and slow moving).
Lava builds up to produce a steep-sided cone. It is common
for the vent of this type of volcano to become blocked.
Pressure builds up and some times the side of the cone is
blown apart, as in the case of Mount St. Helens in the USA.

14. A shield volcano is shallow in shape.
These volcanoes have more runny lava (called basic lava)
which flows relatively slowly down the long gentle sloping
sides of the volcano. These volcanoes often erupt gently for
months or even years.
Shield volcanoes occur at constructive plate boundaries.
Example: Volcanic island of Iceland, Hawaiian Island
volcanoes such as Mauna Loa.

16. Research at home, or in class in your books, at the end of the lesson.
Causes and effects of a volcanic eruption.
Mount St Helens. Washington. USA.
Answer the following:
Where is Mt St Helens?
Briefly explain the processes that produced the eruption of May 1980.
Describe the primary physical impacts of the eruption.
Describe the secondary physical and cultural impacts of the eruption.