Basaltic volcanoes are the most common volcanic landmasses on the continents. They are found where the mantle rises up to form new plates. Basaltic volcanoes are rarely found above the sea surface. Basaltic lava flows freely. Its’ cooling surface forms a skin, which wrinkles and puckers with the movement beneath. This ropey lava is known by its’ Hawaiian name ‘pahoehoe’. If this surface breaks up, it form blocks of lava with rough surfaces, also known as ‘aa’ An active andesitic volcano is extremely violent. The eruptions can happen at any time and the eruptions can cause considerable damage.This type of eruption can also send huge clouds of hot ash and dust over great distances. Andesitic volcanoes are more dangerous than basaltic volcanoes because the lava in andesitic volcanoes is more viscous. This causes the lava to get clogged up in the volcano, then when it does erupt the lava suddenly breaks through causing a great explosion.
A volcano is formed when two tectonic plates hit each other. One of the plates goes under the other. This is where the earth heats rock into magma and gases. This can happen as deep as 150 kilometres below the earth’s crust. Magma settles in pools or chambers near the surface. This is where the eruption takes place. Volcanoes can also be formed when the plates push away from each other and the magma pushes up and lava forms. These types of volcanoes are found on the ocean floor. Cross section of a volcano. Cross section of a volcano erupting. Cross section of a volcano.
Deep in the earth mantle there are areas that are very turbulent and hot. These are known as hot spots, they create the right conditions for basaltic volcanoes to form. When a plate is continuously moving it can creates a string of volcanoes. When a tectonic plate moves over a hot spot, a volcano forms on the surface as rising material breaks through. This happens over and over again and eventually there is a chain of extinct basaltic volcanoes that stretches across the ocean. Ring of fire. Cross section of a hot spot volcano World map of hot spots Diagram showing how hot spot volcanoes are formed
Most volcanoes are found under the seabed. Because the ocean floor is very thin, it can be easily pierced by the magma which lies beneath especially on the plate margins. When the tectonic plates move apart, the rising magma seeps up into the gap, and hardens into a new strip of crust. This type of plate margin is present in the Atlantic Ocean, making the Atlantic wider and forcing Europe and America apart. Active underwater volcanoes usually erupt very violently. Hot molten lava explodes when it hits cold seawater and produces thick black clouds of steam and ash. Under water volcano erupting. Diagram of an underwater volcano erupting. Underwater volcano erupting. Diagram of underwater volcanoes.
There are thousand of volcanoes on Venus. That is why the planet has such a thick atmosphere. Scientist don’t know if any of the volcanoes are still active. Mars is only half the size of earth but the volcanoes there dwarf the tallest mountains on earth. However, all the volcanoes on mars are extinct. Jupiter's moon is the most volcanically active planet or moon in the solar system. A noxious mixture of molten and gaseous sulfur dioxide is spewed from its surface. Volcanoes are not always hot. A space probe that passed Triton in 1989 discovered large geysers on Neptune's moon Triton that erupt with super cold liquid nitrogen. Billions of years ago the Earths moon was volcanically active. The dark patches we can see on the surface are lakes of solidified lava. Venus Mars LoTritonThe Moon
Mt. St. Helens is located in Skamania county in Washington. It erupted on the 18 th of May 1980 after lying dormant for 120 years. Scientists had been watching the volcano for months. There was a huge bulge in the volcano’s side because the lava was moving upward and therefore an eruption was imminent. The blast ripped a huge hole in the once cone shaped volcano, flattened forests for miles around and rained ash over cities as far away as Oklahoma. Fifty seven people died when Mt. St. Helens erupted. BeforeAfter The crater in the cone of Mt. St. Helens. Mt. St. Helens erupting. Diagram of the stages in which Mt. St. Helens erupted.
Krakatau erupted on the 27 of August 1883. It was an ultra plinian eruption, 20 cubic kilometres of tephra, ash and lava was blasted out of the volcano. The bang that Krakatau made when it erupted is said to be the loudest sound humans have ever heard. The eruption obliterated the volcanic cone of Krakatau and destroyed the island in which it sat. 36,417 people died including the victims of the tsunamis that were generated by hot pyroclastic flows entering the ocean. Now a new volcanic cone, Anak Krakatau, has risen from the seafloor where Krakatau once stood. Anak Krakatau Lava erupting from Krakatau. Photo taken of Krakatau erupting in 1883.
Mt. Vesuvius is located in Italy near Pompeii. It has erupted a few times, the most famous of those eruptions was in 79 AD on the 26 th of May. Eight cubic kilometres of ash, dust and rocks was blasted out of the volcano and covered Pompeii. In 1743 the exploration of the ancient site began. When Mt. Vesuvius erupted, over 2,000 people were covered by lava and hot ash. When the lava set and the bodies of those people decayed a hole was left in the shape and position that the people died in. A plaster cast of a dog found in Pompeii Recreation of Mt. Vesuvius erupting 79 AD. Plaster casts of people found in Pompeii A 2 nd recreation of Mt. Vesuvius erupting 79 AD.
Toba is found on the Indonesian island of Sumatra. It erupted approximately 73,500 years ago. The eruption was ultra plinian. There was an eruptive volume of about 2,800 cubic kilometres. After the eruption volcanic ash and sulfur dioxide aerosols injected into the stratosphere and formed a thin layer surrounding the globe that partially blocked the suns rays. This caused a long cold volcanic winter. Some scientists have speculated that this eruption brought humans to the brink of extinction. But Toba wasn’t the biggest volcanic eruption ever, the eruption of La Garita in Western United States approximately 27,000,000 years ago, was almost twice as big. The Plinian column. Toba as it is today
Tell me one fact that you find interesting. (I hope you’ve been listening!)
To find all the information for my PowerPoint presentation on volcanoes, I used many books they are: ‘Volcanoes and Earthquakes’ by Terry Jennings ‘Volcanoes and Thermal Springs’ by Josh Wilson ‘Earthquakes and Ancient Volcanoes’ by Bruce Mclish ‘Earth’ By Susanna van rose ‘My Best Book on Volcanoes’ by Simon Adams ‘Volcano’ by Rosie Nelson ‘Earthquakes and Volcanoes’ by Brian Knapp ‘Volcano evacuation’ by Dougal Dixon ‘Encyclopedia of Science’ Susan Mckeever I also used lots of websites to find my information including: www.bbc.co.uk/history/ancient/romans/pompeii_rediscovery_01. shtml#top www.volcanoelive.com/pliny www.volcanolive.com/krakatau.html www.enchantedlearning.com/subjects/volcano/
Thank you for watching my slideshow, I hope that you enjoyed it, and that you learnt something new about volcanoes.