1. Aftershock
An earthquake that occurs minutes or days after a major earthquake. Aftershocks are usually smaller than the first, large earthquake but can cause the collapse of weakened buildings so are still a hazard.
Topic: Living in an Active Zone

2. Ash
Powdered rock fragments thrown from a volcano during an explosive eruption.
Topic: Living in an Active Zone

3. Caldera
A huge hollow in the earth’s surface caused by the collapse of a volcano after a massive eruption.
Topic: Living in an Active Zone

4. Cinder Zone
A volcanic hill that is conical in shape. A cinder cone is formed by the eruption of red hot lava that is thrown from the vent. The globs of lava are full of gas bubbles. They solidify to form pebble-sized fragments of rock that have the texture of honeycomb
Topic: Living in an Active Zone

5. Constructive Plate Margin
Where two plates are pulling apart and new crust is created.
Topic: Living in an Active Zone

6. Crust
The outer layer of the Earth which is made of solid rock. There are two different types of crust. The crust under the oceans is very dense but only about 10-12km thick. The continents are made of rocks that are less dense. The continental crust is an average of 35km thick but much thicker than this where there are mountains.
Topic: Living in an Active Zone

7. Deformation
The process of bending and folding the crust. Deformation is caused by plate movement.
Topic: Living in an Active Zone

8. Destructive Plate Margin
Where two plates meet and one is destroyed as it is pulled under the other.
Topic: Living in an Active Zone

9. Fold Mountains
Large mountain ranges that have been formed by folding as two tectonic plates collide into one another. The largest fold mountains in the world are the Himalayas. These are formed by the collision of the Indian plate into the rest of Asia. It is estimated that India is moving northwards at about 50mm per year.
Topic: Living in an Active Zone

10. Geothermal Energy
Energy produced by pumping water into hot rocks. The hot water can be used to heat buildings by passing it through radiators. In other places the rocks turn the water into steam. The steam is then used to turn a turbine so that electricity is generated.
Topic: Living in an Active Zone

11. Island Arc
A group of islands formed by the eruption of volcanoes. When viewed from space the islands make a crescent (or arc) shape in the sea.
Topic: Living in an Active Zone

12. Jökulhlaup
An Icelandic word that means ‘glacial outburst’. This is a sudden flood that is caused by the eruption of a volcano under the ice.
Topic: Living in an Active Zone

13. Lahar
An Indonesian word that describes a flood of water and volcanic ash or a mudslide down the slope of a volcano. Lahars are caused when rainwater mixes with loose volcanic ash. Lahars are very dangerous hazards.
Topic: Living in an Active Zone

14. Liquefaction
A soil process that can occur during a strong earthquake. Water in the soil is forced upwards by the shaking. The water pushes the soil particles apart, turning the ground to jelly. This process causes the sinking (or subsidence) of buildings.
Topic: Living in an Active Zone

15. Mantle
The part of the Earth that lies beneath the crust. The rocks in the mantle are hot and under pressure so they behave rather like plastic and deform. Some rocks in the mantle are molten.
Topic: Living in an Active Zone

16. Oceanic Ridge
Long chains of mountains that run down the centre of several oceans, including down the middle of the Atlantic Ocean. The ocean ridges are formed by plate movement.
Topic: Living in an Active Zone

17. Oceanic Trench
Long, deep gorges in the sea bed that occur around the edges of some oceans including the Pacific Ocean. The ocean trenches are formed by plate movement.
Topic: Living in an Active Zone

18. Plate Margin The boundaries of the Earth’s plates where they meet.
Topic: Living in an Active Zone

19. Plates
Rigid sections of crust. The plates lie on top of the mantle. They are able to move relative to each other. The movement is slow, but the force generated by their movement creates earthquakes and volcanic hazards.
Topic: Living in an Active Zone

20. Primary Hazards
Events which cause risk to human life during a volcanic eruption (such as pyroclastic flow) or earthquake (such as buildings collapsing due to the ground shaking).
Topic: Living in an Active Zone

21. Pyroclastic Flow
A landslide of hot ash, rocks and gases from a violent volcanic eruption. Pyroclastic flows move at great speed. They usually contain gases that are several hundred degrees celsius.
Topic: Living in an Active Zone

22. Rift Valley
A steep sided valley formed by the pulling apart (or rifting) of the Earth’s crust during plate movement.
Topic: Living in an Active Zone

23. Secondary Hazards
Events which cause risk to human life sometime after a volcanic eruption or earthquake. For example, the spread of disease after an earthquake is a secondary hazard.
Topic: Living in an Active Zone

24. Shield Volcano
A large volcano that has gentle slopes. Some of the volcanoes in Iceland and Hawaii have this shape.
Topic: Living in an Active Zone

25. Strato-Volcano
A large, steep sided volcano formed from layers of solidified lava and ash that have been built up by many different eruptions.
Topic: Living in an Active Zone

26. Subduction Zone
The region on the earth’s crust where one plate is destroyed as it is slowly pulled underneath another plate.
Topic: Living in an Active Zone

27. Subglacial
Any process or feature that occurs beneath a glacier or sheet of ice. In Iceland there are several powerful subglacial volcanoes that erupt under ice.
Topic: Living in an Active Zone

28. Supervolcano
A volcano that erupts with the greatest possible force and produces the largest amounts of ash and other materials.
Topic: Living in an Active Zone

29. Tephra
A term that describes all the fragments that are thrown from a volcano during an eruption. The hot rocks are full of gas when the volcano erupts so tephra often has a honeycomb texture (like pumice).
Topic: Living in an Active Zone

30. Tiltmeter
A scientific instrument that is used measure tilting of the ground. Tiltmeters can be used to measure small changes in ground shape that occur when the magma chamber beneath a volcano is filling with molten rock.
Topic: Living in an Active Zone