Magma
Magma forms below the Earth's surface in the region that is includes. . .
The lower crust and upper mantle
A large number of volcanoes lie directly on . . . ?
Tectonic plate boundaries
At a divergent boundary, as the plates separate a deep crack is formed, this is called a ?
Rift
________ are places on the Earth's surface directly above columns of rising magma or mantle plumes.
Hot spots
Although extremely hot, most rock in the mantle stays solid because of ?
Pressure from weight of the rock above it.
There are SO many volcanoes on the Pacific Ocean plate boundaries, that they have earned the name?
The Ring of Fire
When mantle material rises to fill the gap in a rift it decreases the pressure of the rock which means that the mantle rock can?
melt into magma
________ volcanoes are those that have not erupted and never will, while _______ volcanoes are those that are not currently erupting but could.
Extinct/Dormant
Rock melts and forms magma when _____ increases and _______ decreases.
Temperature increases
Pressure decreases
Why do so many volcanoes lie on plate boundaries?
It is easier for magma to travel upward through the crust at these points.
The area in the ocean where the magma continually rises and creates new crust is called?
Mid-ocean ridge
Just before an eruption the number and intensity of small ______________ increases.
earthquakes
What usually causes magma to form?
The decrease in pressure since temperature is usually constant.
The Ring of Fire contains what % of the worlds active volcanoes on land?
nearly 75%
At a convergent boundary, the movement of one plate under another is called?
subduction
The change in slope, such as a bulge, of a volcano can predict an eruption - a ___________ is used to detect this.
tiltmeter
Once formed, magma rises towards the Earth's surface why?
magma is less dense than the surrounding rock.
One of newest methods of predicting eruptions rely on images taken from ___________. They look at infrared images taken from 700km above the Earth.
Satellites
At a convergent boundary, the water is released as the rock is heated, this allows the rock to be melted because?
the water lowers the rocks melting point.
The ratio of certain gases changes when an eruption is coming, what two gases are looked at?
Carbon dioxide (CO2) and Sulfur Dioxide (SO2)