Volcanoes are a Blast!
Today, there are many active volcanoes throughout the world. These colossal monuments represent fragmented windows of time that reveal our planet's primitive origin. Volcanoes are mountains that come in various shapes and sizes, some of which are found towering tens of thousands of feet high, while others are broad and flat and stretch for several miles across Earth's landscapes. During an eruption, we are reminded that our planet Earth is ever-changing and will continue to do so throughout the ages.
Tall, steep-sided volcanoes, composed of successive layers of different types of volcanic products, are called composite volcanoes. They may also be referred to as stratovolcanoes because these volcanoes are made up of alternating layers of pyroclastic debris and lava flows. Composite volcanoes are very common and form in parts of the world where viscous magma reaches Earth's surface. When they erupt, they often do so extremely violently. Many of the world's most famous volcanoes, such as Mount St. Helens and Etna are of this type. Composite volcanoes generally have a combination of volcanic eruptions that may include: ash and pyroclastic debris shot into the air, slow-moving lava flows, pyroclastic flows, steam, dangerous gases and lahars (volcanic mud flows).
Shield volcanoes are the giants of the world. These quiet erupting volcanoes are shaped like broad, upturned shields that are made up of layer after layer of runny lava that flowed over the surface and then solidified. Shield volcanoes are typically formed above hotspots. All volcanic islands are composed of an igneous lava rock called basalt. Shield volcanoes typically have fast-moving lava flows, erupting fissures, lava tubes, and lava fountains. As a shield volcano progressively approaches its time of dormancy, it may become more violent in nature. Such volcanoes have lava flows that are mafic in composition, very hot temperatures, and predictable paths for destruction.
Cinder cones are relatively small and composed mainly of loose volcanic cinders (glassy fragments of solidified lava) and ash. They are also called scoria cones because they will often produce the igneous rock scoria. Cinder cones can also form on the sides of both shield and composite volcanoes. Very seldom will lava flows occur, but if they do, they are most often flowing out from the flanks of the cones. There are many cinder cones found in New Mexico and Arizona. Cinder cones often start out as small fissures that suddenly appear out of nowhere in the ground and start spewing cinders and lava bombs.
A small number of volcanoes across the world are said to be Supervolcanoes. Such volcanoes are of cataclysmic eruptions in the past and are capable of future eruptions that could radically alter landscapes and severly impact the world's climates. Super-volcanoes are considered capable of future, similar eruptions. A prime example of one is the Yellowstone Caldera, which makes up a large part of Yellowstone National Park in Wyoming. In this park, a large magma chamber lies about 5 miles below the caldera. Uplifting of the rock dome above the magma chamber or a big increase in earthquake activity could herald a new eruption that would directly affect most all of North America.
Fissure eruptions are voluminous outpourings of lava and poisonous gases that come from linear cracks that appear above ground. Most eruptions are fairly quiet, that is without loud explosions, but their effects can be quite dramatic. In fact, in the past, they have caused climate changes and mass extinctions. Fissures occur mainly in parts of the world where the Earth's crust is stretching, usually at a divergent plate boundary where rifting occurs. The lava flows are thin and runny and can flow for considerable distances. The lava flows cool to form basalt.
Mud volcanoes are less well-known and do not erupt with lava and ash. Such volcanoes are channels through which large amounts of gas, salty water and mud are expelled from deep underground onto Earth's surface. Once these volcanoes dry, and additional eruptions occur later, the mud builds up into cones that can be up to several hundred feet high. Depending on the volcano, these spew out mud which varies in temperature and viscosity. Mud does not erupt from the hot mantle but the crust; therefore, the mud flows are generally cold to luke warm. When underground pressure is high, the mud volcanoes generally break rock formations and throw out chunks of rock with the mud.
Calderas measure anywhere from 0.6 to 60 miles wide. Most are formed by the collapse or subsidence of the central part of a volcano, while there are a few where the entire region has been excavated by a very explosive eruption. Such volcanic eruptions are comparable in violence to asteroid impacts. Calderas should not be confused with craters. Craters are significantly smaller and are formed by the building up of material around a vent rather than the collapse of material below within the magma chamber. The photo to the left is a caldera from the Andes mountains. Such calderas may eventually fill up with water.
Located in the Black Rock Desert of Nevada, this unique geothermal geyser consist of three colorful cones, each continuously spouting hot water. These formations formed accidentally in 1964 from a geothermal test well which was inadequately capped. The scalding water has erupted from the well since then, leaving calcium carbonate deposits growing at the rate of several inches per year. The brilliant red, orange, yellow, and green coloring on the mounds is from thermophilic algae thriving in the extreme micro-climate of the geysers. Unfortunately, these unique volcanic features are not open to the public.
Fumaroles are openings in the planet's crust that emit steam and a variety of volcanic gasses, such as carbon dioxide, sulfur dioxide, and hydrogen sulfide. These unique volcanic features often make loud hissing noises as the steam and gasses escape. Many fumaroles are foul smelling. Unlike hot springs, the water in fumaroles get heated up to such a high temperature that it boils into steam before reaching the surface. The main source of the steam emitted by fumaroles is ground water heated by magma lying relatively close to the surface. Fumaroles are present on active volcanoes during periods of relatively quiet between eruptions. Photo was taken at Yellowstone National Park.