Volcanic Eruptions and Structures

1. Volcanic Eruptions and Structures Extrusive structures Intrusive structures

2. Global Pattern of Volcanoes • Prior to the acceptance of the theory of Plate Tectonics geologists were aware of the location of volcanoes around the rim of the Pacific Ocean and called it the “Ring of Fire”. • They now know it coincides with Plate Margins. • Major volcanoes are associated with three tectonic settings • Subduction zones • Construction zones • Hot Spots

3. Why do volcanoes erupt? • The extrusion of magma on to the earth’s surface is as a result of circulation and gases in the asthenosphere. • Plates being subducted are forced so deep into the asthenosphere that they melt and turn to magma which rises with the aid of gases to form volcanic mountains etch.

4. Intrusive Structures • Magma intruded into the earth’s crust where it cools slowly and solidifies to form rock masses called PLUTONS. Extrusive Structures • Volcanic Material that is extruded on the crust of the earth. These take the form of Lava Plateaus and Volcanic Cones.

5. Volcanic Materials • A wide variety of materials and liquids are ejected during volcanic eruptions. These include • Lava • Gases • Rock

6. Lava • This is only a small art of the output of Volcanoes. • Lava flows are a minor safety hazard • They travel slowly • There are two types of Lava • Basic Lava • Acid Lava • The difference lies in their viscosity

7. Basic Lava • Low in silica content • Very hot (over 1000 degrees Celsius) • Very runny (low viscosity) • Gases can escape easily • Takes a long time to cool & solidify • Flows over long distances • Produces gently sloping landforms

8. Acid Lava • High in silica content • Less heat (800 degrees Celsius) • Pasty (high viscosity) • Gases find it difficult to escape so eruptions are violent • Cools and solidifies quickly and travels short distance • Landforms steep sided and localised

9. Volcanic Gases • Steam • Carbon monoxide • Carbon dioxide • Sulphur dioxide • Hydrogen

10. Pyroclastic Material • Collective name for the huge quantities of broken rock that erupt from a volcano • Ash – fine dust like particles • Cinders – pea sized particles • Bombs – several centimetres in diameter

11. Pumice • Rock material that has so many air spaces formed by trapped gas that it can float • Pyroclastic flows can take the form of • Mudflows • Lahars • Nuée ardente • This is a collective mass of gases, steam, dust and other volcanic particles • It can move at speeds of 500km/hr and travel 100km from source

12. Volcanic Eruptions and Structures • Extrusive The two most common structures are lava plateaus and volcanic cones Intrusive

13. Fissure Eruptions • Flows well up through a linear crack in the crust • Large amounts of Basic Lava • Cover large areas • Can be 50m thick and spread 50km from source • Antrim Derry Plateau

14. Central Vent • Standard idea of a Volcano • Lava and other volcanic materials pour out from a central vent or opening • The pipe connects the magma chamber with the surface • The result is a cone shaped mountain • The materials that erupt will dictate the shape of the volcano

15. Central Vent - Features • Crater – Summit (top) of Volcano a steep sided depression called a Crater • Caldera - A violent eruption may take place leaving a large basin shaped depression called a Caldera

16. Parasitic Cone - The Vents of the Volcano may become plugged and so it is easier for magma to emerge from a secondary vent. This creates a new cone called a Parasitic Cone • Fumaroles – Secondary vents that emit only gases

17. Cinder Cone • This is formed from ash, cinders, rocks and volcanic bombs. • Its formation is associated with a violent eruption. • Force of eruption causes the fragmented lava through the air where it cools and solidifies into various sizes. • They fall around the vent to form a steep sided cone. • E.g Parcutin in Mexico

18. Composite Volcano • Also called a Strato Volcano • Symmetrical structure due to alternate layers of lava and Pyroclastic materials • Most of the Pyroclastic material fall to the base of the volcano so when the lava flows the layers create a concave shape • These volcanoes are one of the most violent e.g. Mount Vesuvius

19. Dome Cone • Formed from viscous ACID Lava • So thick that it is barely able to flow • Cools and solidifies to form a bulbous mass • Domes often block vents trapping gases – as pressure increases an explosion occurs destroying the dome – e.g. Mt. St. Helens in the USA

20. Shield Volcano • This develops due to successive flows of low viscosity BASIC Lava. • These flows are capable of covering large distances and can be referred to as “Rivers of Fire”. • This volcano is a broad based gently sloping structure • Eruptions are gentle and volcanic gases escape easily • Mauna Loa Hawaii (base 120km – 6000m below sea level and 4000 above the water – making it the tallest mountain on Earth)

22. Hot Springs and Geysers • Ground water circulates at great depths in regions of recent volcanic activity it becomes heated and may return to surface as hot springs and geysers • A hot spring – a spring where water is warmer than temperature of human body – they contain dissolved minerals and are thought to have medicinal properties – Vichy France and Blue Lagoon Iceland • Hot springs that intermittently eject hot water and steam (50m) with huge force are called Geysers.

24. Lassen Volcanic National Park Calderas Volcano World More Volcanoes

25. Intrusive Structures • Magma that is intruded into the earths crust will form a number of granite structures called PLUTONS. • These are revealed by uplifts and exposure to denudation • Magma is capable of forcing its way into the bedding planes of sedimentary rocks forcing stratified rock to bulge upwards.

27. Dyke • Vertical sheet of Magma is injected into fractures in the layers of rock • They vary in thickness from a few cms to several metres • They can extend across the country side for several metres

28. Sill • Horizontal sheet of magma injected into layers of sedimentary rock • Formed close to surface of the crust where overhead pressure is low • Laccoliths and lopoliths are variations of a sill • If overlying rocks are arched upwards a dome of igneous rock is called a Laccolith • If overlying rocks are arched downwards the formation is called a Lopolith

30. Batholith • Largest type of Pluton • May be up to 20km deep and hundreds of KM in width. • They are formed deep down and as a result the magma cools very slowly • This slow cooling means the granite is very coarse • They are formed when magma forces its way into the crust – it melts and pushes aside surrounding rock to make room for itself • The Leinster Batholith is the largest Batholith in Britain or Ireland.

32. Level of Volcanic Activity • A more precise classification of Volcanic Activity is required as “Active, Dormant and Extinct” are not totally accurate as many extinct volcanoes can an do come to life • The following are more precise……

33. Volcano Classification • Active live volcano – currently erupting • Dormant live volcano – not erupting but has a high probability of erupting • Dead volcano – most of these have erupted only once and are unlikely to erupt again

34. Predicting Volcanic Eruptions • Main ways are • Seismometers – detect all movements - tiny earthquakes • Lasers and tiltmeters – detect physical swelling in the slope of volcano • Chemical sensors to monitor the sulphur dioxide levels near the crater

35. Effects of Volcanoes • Benefits • Formation of metal and gems including gold copper silver and mercury (Kimberly South Africa old volcano contains the richest concentration of diamonds in the world) • Popular Tourist attraction – Yellowstone National Park – “Old Faithful, USA” • Slopes can be used for winter skiing • Fertile soils – due to mineral nutrients • Thermal energy harnessed in New Zealand and Iceland

36. Effects of Volcanoes • Negative Effects • Destructive effects on people and property • Can cause Mudflow or Lahar – Navado del Ruiz • Tsunami e.g. Krakatoa (Indonesia) in 1883 – 5000 times greater than the nuclear bomb that destroyed Hiroshima

37. Geothermal Energy • This is produced when underground heat is transferred to the surface by water that is heated through contact with hot rock and magma. • These regions lie close to plate margins.

38. Geothermal Energy in Iceland • Iceland is positioned on the Mid Atlantic Ridge • It is therefore a very volcanic location • Water superheated provides a source of energy • Iceland does not have any fossil fuels and therefore its geothermal reserves provide a fuel source and help reduce their imports of other fuels.

39. Mount St. Helen’s • March 20th 1980 series of minor earthquakes indicated new tectonic activity • Soon the volcano began to emit ash, steam and lava • Few weeks later these emissions stopped but minor earthquakes continued • A bulge appeared on the north side – up to 100m • May 28th 1980 an earthquake of magnitude 5 on the Richter Scale shook the volcano • The north slope that had been bulging broke and rushed down the mountain

40. Mount St. Helen’s • Gas, Steam & Dust were released in a great blast – rushing down mountain at speeds of 400km/hr – devastating zone of 20km • A dust cloud rose 20km into the atmosphere • More eruptions continued until early afternoon – then it activity ceased.

41. Consequences of this Eruption • Summit destroyed – reduced by 400m • Eruption melted snow and ice which combined with volcanic debris led to a mud slide which flowed down hill destroying roads and bridges. It filled the valley floor by 60m. • Every tree within a 25k radius was destroyed and wildlife killed. • The Ash Cloud that formed from the eruption brought total darkness to an area stretching 250km to the east. • Ash was deposited on farm land which destroyed crops. • 60 people were killed many of these were disaster tourists and geologists.

42. Volcanic Activity in Ireland • Ireland has little or no volcanic activity at present. This is due to our location within the Eurasian Plate. We are not close to plate margins or hot spots. • There is evidence that Ireland did experience volcanic activity in the past. • The Antrim Derry Plateau and the Leinster Batholith are evidence of this.

43. Antrim Derry Plateau • Plateau covers an area of 4000 square kilometres an is the result of volcanic activity 65 million years ago. • It was formed when the American plate was breaking away from the Eurasian plate leading to the formation of the Atlantic Ocean. • Fissures was caused by this movement and lava poured up from these fissures to form the plateau. • Following the eruptions uplift took place. • A distinctive feature of the plateau is the 60,000 hexagonal columns of basalt. These formed when molten magma was allowed to cool very slowly after becoming trapped in a river valley.

44. The Leinster Batholith • Largest Batholith in Ireland and Great Britain – 120km long • Occupies 1,500 sq km taking in the Dublin Mountains, Blackstairs Mountains and the Wicklow Mountains. • Consists of 5 Granite domes. • Sedimentary rock that had been folded was invaded by molten magma. This magma caused some of the surrounding rock to change (metamorphosed) to Quartzite. The Domes cooled slowly to form Granite Domes.

45. Leaving Cert Examination 2007-09-21 1. “Plate boundaries are zones where crust is both created and destroyed”Examine the above statement, with reference to examples you have studied. • The Theory of Plate Tectonics explains how the earth’s crust is broken into 7 large plates and several minor ones. • The zones at which these plates meet are called plate boundaries. • Plate boundaries mark. the region where new crust is being created or destroyed. (or some times neither created or destroyed – Transform Boundary) • Plates float on a semi plastic layer of the mantle called the Asthenosphere. This is molten and heated by the heated of the core. This heating creates convection currents which drive plates together or apart. • The zones where plates are being driven apart are called “Construction Zones”. The reason for this is that new crust is being created as the plates are forced apart and magma rushes up from the mantle to fill the gap made by the spreading plates. • The Mid-Atlantic Ridge is one example of a Constructive Plate Boundary. It is an underwater mountain range formed by the separating plates (Eurasian and North American) • The zones where plates are being pushed together are called “Destruction Zones”. Here crust is being pushed together and being destroyed or altered. • Due to the two types of crust – oceanic and continental – there are three destructive boundaries to examine. • The first is the oceanic – continental boundary where the old heavy oceanic plate is subducted under the lighter less dense continental plate. (Nazca plate and South American Plate) • The oceanic plate is pulled down into the mantle where it melts and turns into magma and gases. Sometimes this magma will propel itself up to the crust and form Volcanoes. • Where an destructive oceanic – oceanic plate margin occurs the older of the two plates is subducted and melts as above. (Pacific Plate and the Philippines Plate) • Where a destructive continental – continental plate margin occurs neither is likely to subducts so a buckling of the plates takes plate for form fold mountains.(Indian Plate and the Eurasian Plate)

46. Q2. Referring any one of the following examine how humans interact with the rock cycle: - Geothermal Energy • Geothermal energy of volcanoes is harnessed for domestic heating and electricity generation in countries such as New Zealand and Iceland. • Iceland’s position on the Mid-Atlantic Ridge mans that it is the location of much volcanic activity. • Man has been able to harness this energy and use it as an important resource for the Icelandic Economy. • The Magmas of the Hengill Volcano in south Iceland have created a high temperature field of about 200 degrees Celsius……… • Cold water pumped into wells that have been drilled in rocks • Steam returns to the surface via another series of wells • This steam is used to drive a number of electrical plants that provide electricity to the local area. • After this it is piped to another electrical plant where it is used to heat the water of the nearby lake. • This water is heated to 80 degrees Celsius. It is pumped 16 miles to the capital city Reykjavik where it is used to heat homes, offices and industry. • This has enabled Reykjavik to become one of the cleanest cities in the world. • This water now much cooler is piped under the soil in nearby greenhouses to help with the production of plants and vegetables. • Geothermal energy has also created a number of hot pools and spas which are an excellent tourist attraction. • One such example is the Blue Lagoon.

47. Examine the processes that led to the formation of any two volcanic landforms • You will need to outline how volcanoes are formed • Tectonic Processes • What do volcanoes emit? • How does what they emit effect their shape and characteristic • Taking two examples say how they were formed. • Good example here would be Dome (Mt St Helens) and Shield – Mauna Loa