Living in an Active Zone Revision

Cross section of the Earth

Structure of the earth Earth is made up of four distinct layers Crust (oceanic/ Continental) Mantle Outer core Inner core

Structure of the earth Crust is broken up piece called tectonic plates 7 large plates and 12 small plates These plates move because of Convection Currents in the magma Where two plates meet is a plate margin

Why do the plates move?

Constructive Plate Margins Two oceanic plates move away from each other shield volcanoes form creating mid ocean ridges e.g. mid Atlantic ridge. When two continental plate move apart a rift valleys are formed. Shield volcanoes found here e.g. Iceland

Constructive plate boundary

Constructive Plate Margins

Destructive Plate Margins Oceanic and continental Crust Where it involves oceanic and continental crust, the oceanic crust is always subducted below the continental because it is denser. The subduction of the oceanic crust creates a deep sea trench and earthquakes are formed at the subduction zone. Fold mountains are created on the continental crust . The subducted oceanic crust melts in the mantle rising up into the fold mountain to create composite volcanoes E.g. Mount St Helens

Destructive plate boundary

Destructive Plate Margins Oceanic crust only Destructive plate margins also can involve two oceanic plates Here island arcs are formed in the oceanic crust E.g. Montserrat, Caribbean

Destructive Plate Margins

Types of Volcanoes Shield Volcanoes found on constructive plate margins. Lava is hot and runny. Not as explosive. Not very high. Very wide base Composite volcanoes found on destructive plate margins. Thick stick lava. Erupt explosively. Very tall cone shaped.

Volcanic hazards Lava flow Ash Lahars Lava bombs Pyroclastic flow

Volcanic Hazards

Earthquakes – Causes Earthquakes are cause by shock waves travelling through the earth crust The source of the earthquake is called the focus, the epicentre is the point immediately above it on the surface Size of an earthquake can be measured by a seismometer along the Richter scale Tsunamis are a secondary hazard of an earthquake

Epicentre Focus Seismic waves

Earthquakes - Factors Strength of the earthquake Distance from epicentre Depth of the focus Number of people living in an area Type of rock Time of day The extent of preparation

Why do people live there? 500 million people live in active zones Dramatic scenery created attracts tourists, bringing income to an area e.g. Mount Vesuvius, Italy Lava and ash provide nutrients to the soil, making the land near volcanoes very fertile and good for agriculture. E.g. Mount Etna, Italy Opportunities to generate electricity using the heat from the earth (geothermal energy) E.g. Iceland Volcanic rock is a good building stone Many people cannot afford to Move (LEDCs) E.g. Mount Pinatubo, Philippines Tectonic hazards are rare and often to affect an area in a persons lifetime E.g. Montserrat volcano had not erupted for 300yrs until recently Prediction and earthquake resistant building are improving. E.g. Kobe Japan has many earthquake proof buildings DON’T FORGET YOU NEED TO GIVE EXAMPLES

Predicting and preparing - Earthquakes Laser beams used to detect plate movements Seismometer used to pick up vibrations Radon gas – escape from the cracks in the crust before an earthquake – this can be monitored Preparing Educating people via TV or in schools what to do Earthquake drills to prepare Earthquake proof buildings, designed to absorb the energy of an earthquake and withstand movement

Predicting and preparing - Volcanoes Remote sensing – satellites monitor temperature and gas emissions Seismometers – measures earthquakes activity that occurs before an eruption Tiltmeters – monitor changes in the shape of a volcano as it fills with magma Gas emissions – indicate an increased risk Ultra sound – to detect movements of magma Preparing Exclusion zones created around volcanoes Authorities must be ready to evacuate Emergency supplies of basic provisions must be gathered Good communication systems in place

This is an alternative casestudy - Miss Kingdom’s class had two different casestudies (New Zealand and Pakistan). It is up to you which one you lean