Natural Hazards Explosive Earth One of the most beautiful pictures taken of the Earth is known as the Blue Marble. Taken from space, it is the epitome of serenity. The Earth really looks like a small marble with swirls of blue, white, green and brown, as it floats placidly in the vastness of space. However, the Volcano Variety picture is misleading, for Mother Earth is geologically restless and Based on history of activity often explodes in acts so violent that we call them, natural hazards. Active: These volcanoes are currently erupting, or exhibiting unrest through earthquakes and/or gas emissions. Natural hazards are defined as, “those Volcano Architecture Dormant: These volcanoes are inactive, but have not been so long elements of the physical environment, harmful A volcano constitutes a vent, a pipe, a enough to be declared extinct. to man and caused by forces extraneous to crater, and a cone. him.” The prefix “natural” shows that these Vent: This is the opening through which Extinct: These volcanoes have been exclude phenomenon that are a result of volcanic material is ejected. A central vent inactive in all of recorded history. human action. An event that causes large underlies the summit crater of the volcano. Based on shape numbers of fatalities and/or tremendous loss It is connected to a magma chamber, of property is a “natural disaster.” which is the main storage area for material Volcanic cone: Volcanic cones are among that is finally ejected. the simplest volcano formations. These are Violent Volcano Pipe: This is a passageway through which built up of ejected material around a volcanic One of the most explosively violent events the ejected magma rises to the surface. vent. Volcanic cones are differentiated into on Earth is that of an erupting volcano as it Crater: This is the iconic bowl-shaped cinder cones, spatter cones, ash cones, and spews forth molten lava. There are few sights depression at the top of the volcano. tuff cones. Cinder cones (scoria cones) are more awe-inspiring than the sight of red-hot Cone: Solidified lava, ashes, and cinder built almost entirely of loose volcanic lava glinting through the cracks on the sooty form the cone and it rises higher with each fragments called cinders. Hot fluid lava clots black crust as the river of molten matter winds eruption. The sides of the volcano often are called spatter. When spewed spatter falls its way through the landscape. The most contain fractures that connect to the central back to Earth the clots weld together and common conception about a volcano is that vent or to shallow magma chambers. solidify, forming steep-sided spatter cones. it is a mountain with a hole (crater) at the top Magma is ejected through the sides of the Fallen ash forms ash cone, which becomes through which the lava escapes. Not volcano via these fractures. Such eruptions a “tuff cone” or “tuff ring” once the loose everybody realizes that unlike most lead to cone-shaped accumulations called ash particles weld together. mountains, which are pushed up from below, parasitic cones. Fractures are also conduits Shield Volcano: Shield volcanoes are volcanoes are built up by an accumulation for escaping volcanic gases, which are formed by easily flowing lava that has low of the same materials that they eject. released through openings called fumaroles. viscosity. Their heights are typically about 1/20th of their widths. The lower slopes are gentle but the middle slopes become steeper and then flatten at the summit. Many of the largest volcanoes on Earth are shield volcanoes. The Mauna Loa (Hawaii) is the world’s largest shield volcano. Stratovolcano: This is a tall, conical volcano with gentle lower slopes that rise steeply near the summit. The summit usually has a small crater. Many of the most dangerous and explosive volcanoes are stratovolcanoes. Examples are Mt. Fuji (Japan), Mt. Mayon (Philippines), and Mt. Agua (Guatemala). Volcanic Eruptions An eruption begins when pressure on a magma chamber forces magma up and out the volcano’s vents. Of course, sideways-directed volcanic explosions (lateral blasts) 56 SCIENCE REPORTER, January 2010 Lava may flow as River of Fire meets the Sea gentle streams called lava flows or it may erupt violently into the air. Rocks shot into the air along with the lava are called pyroclastic rocks. Vented Out Crater Close-up Merapi, Nyiragongo, Rainier, Sakurajima, violent ejection of volcanic debris On any given day, there are Santa Maria, Santorini, Taal, Teide, called tephra. Ulawun, Unzen, and Vesuvius. Ash and fine particles spewed high into about ten actively erupting the atmosphere scatter light and result Monitoring Eruptions in spectacular colours at sunset. volcanoes. Increased emissions of gas and steam are Astronauts on the space shuttle can shoot ejected material at very high indicators that the volcanic activity is on Endeavour (1994) filmed Kliuchevskoi speeds for quite a distance. When the rise. Rising magma also triggers slight as it erupted. The ash plume reached magma reaches the Earth’s surface, it is tremors, the intensity and frequency of as high as 50,000 feet. called lava. Lava may flow as gentle which increases when the magma nears Most volcanic eruptions take place on streams called lava flows or it may erupt the surface. Thus, an earthquake is a sign the ocean floor. These are called violently into the air. Rocks shot into the that a volcano is about to erupt. submarine eruptions. air along with the lava are called Seismographic monitoring is therefore one The largest active volcano is Mauna pyroclastic rocks. The type of eruption way to predict volcanic eruptions. Loa. depends somewhat on the amount of Volcano Facts Etna is thought to be the oldest active gases and silica in the magma. The volcano. The first record of it erupting Most of the ~550 active volcanoes amount of silica determines the viscosity dates back to 1500 B.C. of the magma. Steam is what powers the on Earth are located along the margins After eruption, a volcano may collapse explosion. of adjacent tectonic plates. into the empty, shallow-level magma Indonesia has the highest number of chamber. This leads to the formation active volcanoes, as it is located on The Decade Volcanoes of a steep, bowl-shaped depression a belt of intense volcanic and seismic Sixteen volcanoes have been identified by called a caldera (Spanish for kettle or activity known as the “Pacific Ring of the International Association of cauldron). Volcanology and Chemistry of the Earth’s Fire.” Interior (IAVCEI) as being worthy of On any given day, there are about ten particular study in light of their history of actively erupting volcanoes. Dr Sukanya Datta large, destructive eruptions and proximity Many eruptions are characterized by Scientist NISCAIR posted to Director General's to populated areas. These are: Avachinsky, nonviolent extrusion of lava flows. Technical Cell, CSIR HQ Colima, Etna, Galeras, Mauna Loa, Other eruptions are explosive with Email: [email protected] SCIENCE REPORTER, January 2010 57.