Types of plate margin
Destructive plate margin
Convections currents in mantle push plates together. Oceanic plate (denser) sinks under the continental plate (lighter). proccess = subduction.
Constructive plate margin
Constructive boundry: Plates move apart =cracks and fractures are left. magma in cracks - makes it to surface = volcano + new land formed.
Conservative plate margin
plates sliding past each other. moving in a similar direction At slightly different angles and speeds. they tend to get stuck. this leads to pressure release= earthquake. at this plate margin the crust is neither destroyed or made.
Types of Volcano
Shield: Sloped sides/ gentle eruptions.
Formation: forms on constructive plate boundry and as plates move apart the magma is given a direct route to the surface. lava is non violent and rolls over surface to form gentle slopes.
Composite: Steep sides/ violent eruptions.
Formation: forms on destructive plate margins and as plates collide weak points in the rock allow magma to sneak through. Pyroclastic flow is ejected up into the air and violently settles on the earths crust
Mount St Helen's Case Study - Sunday 18th may
Facts and Figures
type: 2950m composite volcano
1,800m of ash plume into sky - 27th 1980 march
8:30am- earthquake (huge blast)
Buldge growing on the side of Mt growing 1.5m a day
8:32am- may 18th the Landslide starts. earthquake causes buldge to move. top of cryptodome knocked off, exposes magma
Landslide to mudflows 8:33am- 174bn litres of snow melted to form mudflows
blast kills all within 27km to the north
Buldge 135m long/ 30m high
Facts and Figures
Where: Kobe is located in the south east of Japan, near a destructive plate margin.
When: 17th Jan 1995 at 5.46am.
Why: At this plate margin, the Pacific plate is being pushed under the Eurasian plate, stress is built up and when they are released the Earth shakes.
Size on the ricter scale: measured 6.9 on the Richter scale.