tectonic hazards kq 2

Question 1

rift valley and block mountain

Answer 1

formed at divergent continental plate boundaries.
continental plates move apart,
resulting in tensional forces on the plates,
* parts of the crust are fractured and
displaced (faulting).
tensional forces cause the central block of land to sink between 2 parallel faults, forming a rift valley (steep-sided valley).
* The sections that are left standing beside the rift valley are block mountains

Question 2

parts of the volcano

Answer 2

Magma chamber
Crater
Secondary cone
Vent
Cone

Question 3

describe formation of volcanoes

Answer 3

Magma from the magma chamber rises to the surface through vent.
* When eruption occurs, lava, ash and rock fragments are
released.
* When a stratovolcano erupts, pyroclasts released. force of volcanic eruption depends on amount of pressure built up within volcano.
* Over time, alternate layers of ash and lava build up after
repeated eruptions, forming the volcano.

Question 4

describe the developments of volcanoes

Answer 4

the vent may become
blocked. forces the magma to find a new exit to the
surface. A secondary cone of newer volcanic material will then
develop.
* The summit of a volcano may be blown off during an explosive
eruption.
* The sides of the crater collapse inwards due to the loss of
structural support.
* As a result, a large depression known as the caldera is formed.

Question 5

distribution of volcanoes

Answer 5

The Pacific Ring of Fire is found along the boundaries of several converging plates,
namely the Pacific Plate, Nazca Plate, the Philippine Plate, Australian Plate and
the Eurasian Plate.

• Volcanoes are also found where tectonic plates are diverging, such as the
  Atlantic Ocean and East Africa, where volcanoes are formed as magma rises to surface

Question 5

sheild volcano

Answer 5

Common along constructive boundaries
(magma rises from mantle)
* E.g. Mount Washington, USA

Low silica lava
Low viscosity
 Flows more easily and spreads over
a large area before solidifying

Wide/ Broad base
Low height
Gentle slopes

Question 6

stratovolcano

Answer 6

Destructive boundaries (magma rises from
subduction zone)
* Eg. Mount St Helens
High silica lava
High viscosity
 Flows slowly over shorter distances
before cooling quickly and solidifying
 Tends to trap a lot of gas

Violent/ Explosive

(due to the build-up of gases)
 As magma rises towards the Earth’s
surface, the gases expand, causing
an outward explosion.
Narrow base
Taller in height
Steep slopes

Question 7

how do earthquakes occur?

Answer 7

An earthquake is a sudden tremor, vibration or violent shaking of the ground.
* Plate movement along plate boundaries is rough and this creates friction.
* Tension builds up over time.
* When the rocks can no longer withstand the increasing stress, they can suddenly
slip many metres, causing an earthquake.
* The stress is released in the form of seismic waves which radiates out from the
focus

Question 8

deep focus earthquakes vs shallow surface earthquakes

Answer 8

Deep-focus earthquakes occur between 70−700km below the earth’s surface.
The waves generally lose much of their energy by the time they reach the
surface, so there is little impact on the land.

Shallow-focus earthquakes occur in the upper 70km of the crust and generally
have stronger impact as seismic waves reach the land surface quickly.