2. Name: Rajesh Parmar Enrollment No.: 130030106076

3. Subject name: Geotechnics and applied geology Subject code: 2130606

4.  The Layers of the Earth

5.  The Four Layers The Earth is composed of four different layers. The crust is the layer that you live on, and it is the most widely studied and understood. The mantle is much hotter and has the ability to flow. The outer core and inner core are even hotter with pressures so great you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth!

6.  The Crust The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. The crust is only about 3-5 miles (8kilometers) thick under the oceans (oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust).

7.  The Lithospheric Plates The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semi-rigid asthenosphere.

8.  The Asthenosphere The asthenosphere is the semi-rigid part of the middle mantle that flows like hot asphalt under a heavy weight.

9.  The Lithosphere The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere.

10. The Crust The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than the granite. Because of this the less dense continents ride on the denser oceanic plates.

11.  The Mantle The Mantle is the largest layer of the Earth. The middle mantle is composed of very hot dense rock that flows like asphalt under a heavy weight. The movement of the middle mantle (asthenosphere) is the reason that the crustal plates of the Earth move.

12.  Convection Currents The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over.

13.  Convection Currents The next time you heat anything like soup or water in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the asthenosphere they also move the crust. The crust gets a free ride with these currents, like the cork in this illustration. Safety Caution: Don’t get your face too close to the boiling water!

14. The Outer Core The core of the Earth is like a ball of very hot metals. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of the melted metals of nickel and iron.

15.  The Inner Core The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place like a solid.

16. Volcanic Eruptions and Hazards

17.  What is a volcano? A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth’s crust to the Earth's surface. The volcano includes the surrounding cone of erupted material. conduit cone vent magma chamber

18.  How and why do volcanoes erupt?  Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface.  Same principle as hot air rising, e.g. how a hot air balloon works  When magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H 2 O, CO 2, S) it has in it as to how it erupts.  Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption!  Think about shaking a carbonated drink and then releasing the cap.  Small amounts of gas and (or) low viscosity (runny) magma will form an effusive eruption  Where the magma just trickles out of the volcano (lava flow).

19.  Explosive Eruptions  Explosive volcanic eruptions can be catastrophic  Erupt 10’s-1000’s km 3 of magma  Send ash clouds >25 km into the stratosphere  Have severe environmental and climatic effects  Hazardous!!! Above: Large eruption column and ash cloud from an explosive eruption at Mt Redoubt, Alaska

20.  Explosive Eruptions  Three products from an explosive eruption  Ash fall  Pyroclastic flow  Pyroclastic surge

21.  Direct measurements of pyroclastic flows are extremely dangerous!!!

22.  Effusive Eruptions  volcanic eruption dominated by the passive outpouring of lava onto the Earth’s surface is called an effusive eruption.  This happens either because there is not enough gas (volatiles) in the magma to break it apart upon escaping, or the magma is too viscous (sticky) to allow the volatiles to escape quickly.  Remember: molten rock is called “magma” when it is underneath the ground. It is called “lava” once it has been erupted onto the surface.  Lava flows generated by effusive eruptions vary in shape, thickness, length, and width depending on the type of lava erupted, discharge rate (how fast it comes out of the vent), slope of the ground over which the lava travels, and duration of eruption.  Although not generally as hazardous as explosive eruptions, lava flows can burn and bury buildings and forests and do pose a danger to people living on or near an active volcano.

23.  Why do volcanoes grow? A) Repeated eruptions B) There are various types of volcanoes and each forms differently C) Volcanoes were formed when the earth was formed and haven’t changed much since then. D) Both A and B

24. Seismic Activity  Earthquake activity commonly precedes an eruption  Result of magma pushing up towards the surface  Increase volume of material in the volcano shatters the rock  This causes earthquakes

25.  Seismographs are stationed on the flanks of the volcano  These record the frequency, duration and intensity of the earthquakes and report it back to the volcano observatory.  Earthquake activity is measured by Seismographs

27. THANK YOU …