[Applause] [Music] now we're moving on to volcanoes so I'll be talking about their characteristics their formation and their distribution so first of all to summarize what a volcano is it's a vent in the Earth's crust as we can see here through which magma flows this is molten rock and it flows over the Earth's surface where it cools to form volcanic rock and obviously as these layers build up you get that characteristic cone shape that you find with these composite volcanoes now volcanoes expel gases Ash and solid volcanic rock but how do volcanoes form they occur at both destructive and constructive plate boundaries here we see a destructive plate boundary what occurs here is that two tectonic plates push together until one is subducted which means forced beneath the other one as the plate is pushed down the rock melts this builds up pressure underneath the Earth's surface and means that magma can be forced through faults in that crust so I'll just write out the summary here so to summarize the volcano formation at a destructive plate boundary we have our two plates pushing together until one is subducted as the plate is pushed down the rock melts and builds up pressure in the Earth's surface but what about volcano formation at constructive plate boundary so I think that this type of volcano formation is slightly more straightforward here you'll find that the plates are moving apart so the tectonic plates diverge they move apart and magma rises up in order to fill the Gap and there you'll find your volcano May erupt just a tiny extra detail here they could ask you how do hot spots lead to a tectonic Hazard such as a volcano so we're just going to say here that a hot spot they are stores or plums of magma that are pushed through weakness in the Earth's crust to form volcanoes let's talk about the distribution of volcanoes you're going to find them concentrated along tectonic plate boundaries as we see here and specifically around the Pacific Ocean where the Pacific Plate is being subducted beneath the surrounding plates and that's why we call this the Pacific Ring of Fire now we can measure the intensity of a volcano Hazard using the volcanic explosivity index now it's time to turn our attention to the characteristics of volcanoes so we'll be going through things like lava flows ash clouds lava bombs Etc so start starting with the lava flow these May reach as far as 10 km from the volcano crater they'll destroy farmlands and buildings but lives are R lost now ash clouds these are thrown into the air during a violent eruption they may be carried long distances by wind and cause adverse effects in other countries a good example of this is the volcano eruption in Iceland in 2010 which caused Mass travel disruption to many countries hundreds of kilometers away Ash May bury buildings and crops and cause Suffocation or asphixiation of animals and humans now volcanoes Bouch an awful lot of toxic gases when they erupt these include sulfur dioxide carbon monoxide and even cyanide so these are highly toxic gases carbon dioxide is also released but it's not toxic but it is a greenhouse gas which can contribute to global warming sorry about how I've written those symbols but I am a chemist so that's why I've written the chemical formula of those gases what about lava bombs now these are terrifying things due to the build of press pressure large borders of lava may be emitted at high speed causing severe injury and death to any animals or humans caught in their path as we previously me mentioned in another video obviously the tectonic plates moving can be a major source of earthquakes so it's common to get earthquakes where you find Volcano pyroclastic flow this is a fast moving current of hot gas and lava which moves at high speed along the ground away from the volcano this causes damage to crops and buildings and may lead to Serious injury and death and then lastly mudslides maybe not one that you think of immediately but they commonly occur in places which have been littered with volcanic material now we're answering the question why do people continue to live in places at risk from volcano well one very good reason is because of the quality of the soil found close to volcanoes that Ash which gets deposited increases the fertility of the soil and therefore produces good crop yields so increased crop yield serious eruptions may be considered to be rare and therefore not considered a serious threat by residents tied in with this first point the quality of the soil volcanic areas are often rich in mineral deposits which provides people with a potential source of income hence they choose to stay and then it's that matter where so many people have historically lived in an area they have so many settlements present that the family connections people build mean that they do not want to leave the area in spite of all the risks and then when you've got that open vent with the access to the magma it means that you have access to geothermal energy a type of renewable energy resource that provides people with a lowcost source of energy now this bit of the specification deals with the reasons for differing impacts of particular volcano events so why does one particular volcano erupting cause very few deaths very little damage to infrastru structure whilst other volcano events cause huge amounts of damage and destruction so the first point is obviously the location size and length of the eruptive episode will have a huge influence as well as how prepared local areas were for the eruption we've already pointed out the various characteristics of volcanoes so you're not guaranteed all of these characteristics when a volcano erupts so we know that some volcanoes produce more Ash which causes travel disruption very long distances away when we take that Icelandic volcano eruption back in 2010 some produced more pyroclastic flow which cause a lot of injury and death to animals and humans the impact of a will depend on how much preparation has taken place beforehand how much warning they got that it was going to happen so level of preparedness local emergency services in situ SO waiting to come and rescue people as well as warnings telling people to evacuate that will reduce the number of deaths from the the volcano population density is also very key obviously if you've got huge mega cities or even just large settlements close to the volcano they're going to be more vulnerable to any of the lava flows and pyroclastic flow as well as ash clouds [Music]