Transcript Slide 1
Volcanoes • Mountains that erupt lava Lava ACTIVE Z Zz Rock DORMANT EXTINCT Hawaii vent cone Pipe (Conduit) magma chamber Crust • A look at the mantle and crust Mantle Cold air Ocean Hot Melt Hot Mantle Cooler Mantle How do volcanoes erupt? There are two types of eruption: Effusive: Hot magma rises to the surface and flows over the sides Explosive: The Magma has lots of gas in it. As the pressure builds inside the volcano it eventually has too much energy and erupts upwards explosively. We are going to demonstrate an eruption- which type is it? Why? • EXPLOSIVE magma Sticky Lots of Bubbles • EFFUSIVE magma Runny Not many bubbles Hawaii Courtesy of www.swisseduc.ch • ’a’a • Pahoehoe Rough Lots of pieces Smooth or Ropy Courtesy of A. Rust What would you call them? Courtesy of A. Rust Where can we find volcanoes? They form along special places called Tectonic Plate boundaries Where can we find volcanoes? At Tectonic Plate boundaries The tectonic plates are a bit like closely packed iceburgs that move around. Are there volcanoes in Britain? There are no active volcanoes in Britain today – we are not on a Tectonic Plate Boundary BUT Many millions of years ago (about 60 million) we were on a Tectonic Plate boundary. How do geologists know this? How can we find out about volcanoes that existed in the UK a long, long time ago? Geologists are a bit like detectives: They look for clues. 1. The types of rock 2.Rocks under the microscope 3. The landscape Activities The types of rock Geologists have made maps showing where different types of rocks can be found in the UK •Look at the Geological map and find where we live •Where can we find the closest volcanic rock to our school? •Have you visited any of the places marked on the map where volcanic rock can be found? •Now look at the rocks that we have brought from a collection at Bristol University. What do they feel like? How heavy are they? Do they have air bubbles inside them?- thinking back to the volcanic eruption what might have made the bubbly rock? Fill out the table on the back of your Geological map Geologists take a closer look at rocks by taking very thin slices to look at under the microscope. We have brought some with us today so that you can take a look too. Volcanic rocks What did you discover from looking at the rocks? What rock had holes in it? Which rocks had the biggest crystals? Basalt-fine crystals formed as lava cools quickly above ground Pumice Gabbro- fine to coarse crystalsformed underground Volcanic Bomb Granite- magma cools slowly underground and produces large crystals 2.Rocks under the microscope Rocks Under The Microscope Notice the size and shape of the crystals. Both are magnified 11 times Rhyolite Diorite 2.Rocks under the microscope Rocks Under The Microscope Notice the size and shape of the crystals. Both are magnified 12 times Andesite Granite What can the size of the crystals tell us? Small crystals form when the molten rock cools quickly- this happens when the lava flows over the Earth’s surface Larger crystals are formed when the molten rock cools slowly- this happens when the magma is trapped underground. From the rocks you have seen today, which do you think came from underground and which were formed in lava flows above ground? You can test this for yourself by growing your own crystals- some in a warm/hot place and the other in a cool/cold place. We’ll help you set this up as an experiment Evidence of ancient volcanoes in UKlooking at geographical features The landscape Edinburgh, Scotland Lava flow Arthur’s Seat Salisbury Crags Evidence of ancient volcanoes in UKlooking at geographical features The landscape Granite batholith of Dartmoorwas part of a huge underground chamber that was filled with magma. Evidence of ancient volcanoes in UKlooking at geographical features The landscape Staffa's, an island off Scotland has spectacular columns made of basalt formed from a lava flow 60 million years ago. Huge amounts of magma rose up through the cracks in the Earth's crust, erupting as lava and volcanic ash onto the surface. This volcanic activity lasted many hundreds of thousands of years and eventually created a 2.2 km plateau of lava and ash. • Questions V____ ent What are volcanoes?Mountains that erupt l a v a. Lava is very: hot A dormant volcano is: Cone cold awake Conduit M ________ a g m a chamber asleep Why do volcanoes erupt? Hot magma wants to go: How do volcanoes erupt? Two types: e x p l o s i v e What helps make explosive volcanoes erupt? How can we find signs of volcanoes in UK? What does the size of the crystals tell us? up down and effusive b u b b l e. s .