VOLCANOES

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Volcano

A volcano is an opening, or rupture, in a planet’s surface or crust, which allows hot, molten rock, ash and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time.

Volcanoes are generally found where tectonic plates are pulled apart or come together. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by “divergent tectonic plates” pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by “convergent tectonic plates” coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth’s crust (called “non-hotspot intraplate volcanism”), such as in the African Rift Valley, the Wells Gray-Clearwater Volcanic Field and the Rio Grande Rift in North America and the European Rhine Graben with its Eifel volcanoes.

Volcanoes can be caused by “mantle plumes”. These so-called “hotspots”, for example at Hawaii, can occur far from plate boundaries. Hotspot volcanoes are also found elsewhere in the solar system, especially on rocky planets and moons.

Etymology

Volcano is thought to derive from Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn originates from Vulcan, the name of a god of fire in Roman mythology. The study of volcanoes is called volcanology, sometimes spelled vulcanology.

The Roman name for the island Vulcano has contributed the word for volcano in most modern European languages.

In culture

Many ancient accounts ascribe volcanic eruptions to supernatural causes, such as the actions of gods or demigods. To the ancient Greeks, volcanoes’ capricious power could only be explained as acts of the gods, while 16th/17th-century German astronomer Johannes Kepler believed they were ducts for the Earth’s tears. [8] One early idea counter to this was proposed by Jesuit Athanasius Kircher (1602–1680), who witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal.

Various explanations were proposed for volcano behavior before the modern understanding of the Earth’s mantle structure as a semisolid material was developed. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to chemical reactions and a thin layer of molten rock near the surface.

Plate tectonics and hotspots

Divergent plate boundaries

At the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust is being formed by hot molten rock slowly cooling and solidifying. The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates. The release of pressure due to the thinning of the crust leads to adiabatic expansion, and the partial melting of the mantle. This melt causes the volcanism and makes the new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, therefore most volcanic activity is submarine, forming new seafloor. Black smokers or deep sea vents are an example of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, Iceland.

Convergent plate boundaries

Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. The crust is then melted by the heat from the mantle and becomes magma. This is due to the water content lowering the melting temperature. The magma created here tends to be very viscous due to its high silica content, so often does not reach the surface and cools at depth. When it does reach the surface, a volcano is formed. Typical examples for this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire.

Hotspots

Hotspots are not usually located on the ridges of tectonic plates, but above mantle plumes, where the convection of Earth’s mantle creates a column of hot material that rises until it reaches the crust, which tends to be thinner than in other areas of the Earth. The temperature of the plume causes the crust to melt and form pipes, which can vent magma. Because the tectonic plates move whereas the mantle plume remains in the same place, each volcano becomes dormant after a while and a new volcano is then formed as the plate shifts over the hotspot. The Hawaiian Islands are thought to be formed in such a manner, as well as the Snake River Plain, with the Yellowstone Caldera being the part of the North American plate currently above the hotspot.

Types of Volcano

Volcanic features

The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit. This describes just one of many types of volcano, and the features of volcanoes are much more complicated. The structure and behavior of volcanoes depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater, whereas others present landscape features such as massive plateaus. Vents that issue volcanic material (lava, which is what magma is called once it has escaped to the surface, and ash) and gases (mainly steam and magmatic gases) can be located anywhere on the landform. Many of these vents give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Hawaii’s Kīlauea.

Other types of volcano include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter, Saturn and Neptune; and mud volcanoes, which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes, except when a mud volcano is actually a vent of an igneous volcano.

Shield volcanoes

Hawaii and Iceland are examples of places where volcanoes extrude huge quantities of basaltic lava in effusive eruptions that gradually build a wide mountain with a shield-like profile. Their lava flows are generally very hot and very fluid, contributing to long flows. The largest lava shield on Earth, Mauna Loa, rises over 9,000 m from the ocean floor, is 120 km in diameter and forms part of the Big Island of Hawaii, along with other shield volcanoes such as Mauna Kea and Kīlauea. Olympus Mons on Mars is the largest shield volcano and also tallest Known Mountain in the solar system. Smaller versions of shield volcanoes include lava cones, and lava mounds.

Cinder cones

Volcanic cones or cinder cones result from eruptions that erupt mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 meters high. Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones.

Stratovolcanoes

Stratovolcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata that give rise to the name. Stratovolcanoes are also known as composite volcanoes. Strato/composite volcanoes are made of cinders, ash and lava. The volcanoes are made by another volcano. Cinders and ash pile on top of each other, then lava flows on top and dries and then the process begins again. Classic examples include Mt. Fuji in Japan, Mount Mayon in the Philippines, and Mount Vesuvius and Stromboli in Italy.

Super volcanoes

Super volcano is the popular term for a large volcano that usually has a large caldera and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulfur and ash erupted. They are the most dangerous type of volcano. Examples include Yellowstone Caldera in Yellowstone National Park of western USA, Lake Taupo in New Zealand and Lake Toba in Sumatra, Indonesia. Super volcanoes are hard to identify centuries later, given the enormous areas they cover. Large igneous provinces are also considered super volcanoes because of the vast amount of basalt lava erupted.

Submarine volcanoes

Submarine volcanoes are common features on the ocean floor. Some are active and, in shallow water, disclose their presence by blasting steam and rocky debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them prevents the explosive release of steam and gases, although they can be detected by hydrophones and discoloration of water because of volcanic gases. Even large submarine eruptions may not disturb the ocean surface. Because of the rapid cooling effect of water as compared to air, and increased buoyancy, submarine volcanoes often form rather steep pillars over their volcanic vents as compared to above-surface volcanoes. They may become so large that they break the ocean surface as new islands. Pillow lava is a common eruptive product of submarine volcanoes.

Sub glacial volcanoes

Sub glacial volcanoes develop underneath icecaps. They are made up of flat lava flows atop extensive pillow lavas and palagonite. When the icecap melts, the lavas on the top collapse leaving a flat-topped mountain. Then, the pillow lavas also collapse, giving an angle of 37.5 degrees[citation needed]. These volcanoes are also called Table Mountains, tuyas or (uncommonly) mobergs. Very good examples of this type of volcano can be seen in Iceland; however, there are also tuyas in British Columbia. The origin of the term comes from Tuya Butte, which is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analyzed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near the boundary with the Yukon Territory.

Erupted material

Lava composition

Another way of classifying volcanoes is by the composition of material erupted (lava), since this affects the shape of the volcano. Lava can be broadly classified into 4 different compositions (Cas & Wright, 1987):

If the erupted magma contains a high percentage (>63%) of silica, the lava is called felsic.

• Felsic lavas (or rhyolites) tend to be highly viscous (not very fluid) and are erupted as domes or short, stubby flows. Viscous lavas tend to form stratovolcanoes or lava domes. Lassen Peak in California is an example of a volcano formed from felsic lava and is actually a large lava dome.
• Because siliceous magmas are so viscous, they tend to trap volatiles (gases) that are present, which cause the magma to erupt catastrophically, eventually forming stratovolcanoes. Pyroclastic flows (ignimbrites) are highly hazardous products of such volcanoes, since they are composed of molten volcanic ash too heavy to go up into the atmosphere, so they hug the volcano’s slopes and travel far from their vents during large eruptions. Temperatures as high as 1,200 °C are known to occur in pyroclastic flows, which will incinerate everything flammable in their path and thick layers of hot pyroclastic flow deposits can be laid down, often up to many meters thick. Alaska’s Valley of Ten Thousand Smokes, formed by the eruption of Novarupta near Katmai in 1912, is an example of a thick pyroclastic flow or ignimbrite deposit. Volcanic ash that is light enough to be erupted high into the Earth’s atmosphere may travel many kilometers before it falls back to ground as a tuff.

If the erupted magma contains 52–63% silica, the lava is of intermediate composition.

• These “andesitic” volcanoes generally only occur above subduction zones (e.g. Mount Merapi in Indonesia).

If the erupted magma contains <52%>45% silica, the lava is called mafic (because it contains higher percentages of magnesium (Mg) and iron (Fe)) or basaltic. These lavas are usually much less viscous than rhyolitic lavas, depending on their eruption temperature; they also tend to be hotter than felsic lavas. Mafic lavas occur in a wide range of settings:

• At mid-ocean ridges, where two oceanic plates are pulling apart, basaltic lava erupts as pillows to fill the gap;
• Shield volcanoes (e.g. the Hawaiian Islands, including Mauna Loa and Kilauea), on both oceanic and continental crust;
• As continental flood basalts.

Lava texture

Two types of lava are named according to the surface texture: ʻAʻa (pronounced [ʔaʔa]) and pāhoehoe (pronounced IPA: paːhoehoe), both words having Hawaiian origins. ʻAʻa is characterized by a rough, clinkery surface and is what most viscous and hot lava flows look like. However, even basaltic or mafic flows can be erupted as ʻaʻa flows, particularly if the eruption rate is high and the slope is steep. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Usually, only mafic flows will erupt as pāhoehoe, since they often erupt at higher temperatures or have the proper chemical make-up to allow them to flow at a higher fluidity.

Volcanic activity

A popular way of classifying magmatic volcanoes is by their frequency of eruption, with those that erupt regularly called active, those that have erupted in historical times but are now quiet called dormant, and those that have not erupted in historical times called extinct. However, these popular classifications—extinct in particular—are practically meaningless to scientists. They use classifications which refer to a particular volcano’s formative and eruptive processes and resulting shapes, which was explained above.

There is no real consensus among volcanologists on how to define an “active” volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespan of humans or even civilizations. For example, many of Earth’s volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By human lifespan, however, they are not.

Scientists usually consider a volcano to be active if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions. Many scientists also consider a volcano active if it has erupted in historic time. It is important to note that the span of recorded history differs from region to region; in the Mediterranean, recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States, it reaches back less than 300 years, and in Hawaii, little more than 200 years. The Smithsonian Global Volcanism Program’s definition of ‘active’ is having erupted within the last 10,000 years.

Dormant volcanoes are those that are not currently active (as defined above), but could become restless or erupt again. Confusion however, can arise because many volcanoes which scientists consider to be active are referred to as dormant by laypersons or in the media.

Extinct volcanoes are those that scientists consider unlikely to erupt again. Whether a volcano is truly extinct is often difficult to determine. Since “super volcano” calderas can have eruptive lifespan sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct. For example, the Yellowstone Caldera in Yellowstone National Park is at least 2 million years old and hasn’t erupted violently for approximately 640,000 years, although there has been some minor activity relatively recently, with hydrothermal eruptions less than 10,000 years ago and lava flows about 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e. the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be an active volcano.

Effects of volcanoes

There are many different kinds of volcanic activity and eruptions: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.

On June 22, 1989, the Wahaula Visitor Center in Hawaii was engulfed by a lava flow and burst into flames. Note the Lava flow on the left in the Photo Above.

Image Courtesy J.D. Griggs, Hawaiian Volcano Observatory

 

The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.

Large, explosive volcanic eruptions inject water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 16–32 kilometers (10–20 mi) above the Earth’s surface. The most significant impacts from these injections come from the conversion of sulfur dioxide to sulfuric acid (H2SO4), which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the Earth’s albedo—its reflection of radiation from the Sun back into space - and thus cool the Earth’s lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth’s surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The sulfate aerosols also promote complex chemical reactions on their surfaces that alter chlorine and nitrogen chemical species in the stratosphere. This effect, together with increased stratospheric chlorine levels from chlorofluorocarbon pollution, generates chlorine monoxide (ClO), which destroys ozone (O3). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for cirrus clouds and further modify the Earth’s radiation balance. Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon for biogeochemical cycles.

Gas emissions from volcanoes are a natural contributor to acid rain. Volcanic activity releases about 130 to 230 teragrams (145 million to 255 million short tons) of carbon dioxide each year. Volcanic eruptions may inject aerosols into the Earth’s atmosphere. Large injections may cause visual effects such as unusually colorful sunsets and affect global climate mainly by cooling it. Volcanic eruptions also provide the benefit of adding nutrients to soil through the weathering process of volcanic rocks. These fertile soils assist the growth of plants and various crops. Volcanic eruptions can also create new islands, as the magma cools and solidifies upon contact with the water.

 

• Avachinsky-Koryaksky, Kamchatka, Russia
• Colima, Mexico
• Mount Etna, Sicily, Italy
• Galeras, Colombia
• Mauna Loa, Hawaii, USA
• Merapi, Indonesia
• Nyiragongo, Democratic Republic of the Congo
• Mount Rainier, Washington, USA
• Sakurajima, Japan
• Santamaria/Santiaguito, Guatemala
• Santorini, Greece
• Taal Volcano, Philippines
• Teide, Canary Islands, Spain
• Ulawun, Papua New Guinea
• Mount Unzen, Japan
• Vesuvius, Italy
• SOURCE:http://haseembhai.blogspot.com

Glaciers

Glaciers are made up of fallen snow that, over many years, compresses into large, thickened ice masses. Glaciers form when snow remains in one location long enough to transform into ice. What makes glaciers unique is their ability to move. Due to sheer mass, glaciers flow like very slow rivers. Some glaciers are as small as football fields, while others grow to be over a hundred kilometers long.

Donjek Glacier in the Saint Elias Range, Yukon Territory, Canada. 1985. (Source: Natural Resources Canada. Photograph by Douglas Hodgson. Copyright Terrain Sciences Division, Geological Survey of Canada.)

Presently, glaciers occupy about 10 percent of the world’s total land area, with most located in polar regions like Antarctica and Greenland. Glaciers can be thought as remnants from the last Ice Age, when ice covered nearly 32 percent of the land, and 30 percent of the oceans. An Ice Age occurs when cool temperature endure for extended periods of time, allowing polar ice to advance into lower latitudes. For example, during the last Ice Age, giant glacial ice sheets extended from the poles to cover most of Canada, all of New England, much of the upper Midwest, large areas of Alaska, most of Greenland, Iceland, Svalbard and other arctic islands, Scandinavia, much of Great Britain and Ireland, and the northwestern part of the former Soviet Union.

Within the past 750,000 years, scientists know that there have been eight Ice Age cycles, separated by warmer periods called interglacial periods. Currently, the Earth is nearing the end of an interglacial, meaning that another Ice Age is due in a few thousand years. This is part of the normal climate variation cycle. Greenhouse warming may delay the onset of another glacial era, but scientists still have many questions to answer about climate change. Although glaciers change very slowly over long periods, they may provide important global climate change signals.

How is a glacier formed?

Glaciers begin to form when snow remains in the same area year-round, where enough snow accumulates to transform into ice. Each year, new layers of snow bury and compress the previous layers. This compression forces the snow to re-crystallize, forming grains similar in size and shape to grains of sugar. Gradually the grains grow larger and the air pockets between the grains get smaller, causing the snow to slowly compact and increase in density. After about two winters, the snow turns into firn — an intermediate state between snow and glacier ice. At this point, it is about half as dense as water. Over time, larger ice crystals become so compressed that any air pockets between them are very tiny. In very old glacier ice, crystals can reach several inches in length. For most glaciers, this process takes over a hundred years.

Why Do glaciers move?

1951		The sheer weight of a thick layer of ice and the fact that it deforms as a “plastic” material, combined with gravity’s influence, causes glaciers to flow very slowly. Ice may flow down mountain valleys, fan across plains, or in some locations, spread out to the sea. Movement along the underside of a glacier is slower than movement at the top due to the friction created as it slides along the ground’s surface.Glaciers periodically retreat or advance, depending on the amount of snow accumulation or albation that occurs. This retreat or advance refers only to the position of the terminus, or snout, of the glacier. Even as it retreats, the glacier still deforms and moves downslope, like a conveyor belt. For most glaciers, retreating and advancing are very slow occurrences, noticeable only over a long time. However, when glaciers retreat rapidly, movement may be visible over a few months or years. For instance, massive glacier retreat has been recorded in Glacier Bay, Alaska. Other glaciers have been photographed at intervals showing dramatic recession. Alternatively, glaciers may surge, racing forward several meters per day for weeks or even months. In 1986, the Hubbard Glacier in Alaska began to surge at the rate of 10 meters per day across the mouth of Russell Fiord. In only two months, the glacier had dammed water in the fjord and created a lake. This illustrates how quickly a surging glacier can change its surroundings. Retreat of the Franz Josef Glacier: The photographs to the left are selected from a series that show the retreat of the Franz Josef Glacier in New Zealand over a period of 14 years. (World Data Center for Glaciology, Boulder)
1957
1964

What are the components of a glacier?

		Glaciers live a dynamic existence. Several elements contribute to glacier formation and growth. Snow falls in the accumulation area, usually the part of the glacier with the highest elevation, adding to the glacier’s mass. As the snow slowly accumulates and turns to ice, the glacier increases in weight, forcing glacial movement. Further down the glacier is the ablation area, where most of the melting and evaporation occur. Between these two areas a balance is reached, where snowfall equals snowmelt. Here, the glacier is in equilibrium. Whenever this equilibrium is disturbed, either by increased snowfall or by excessive melting, the glacier either retreats or advances at more than its normal pace.Several visible features are common to most glaciers. At locations where a glacier flows rapidly, giant cracks called crevasses are created, which may make travel across a glacier treacherous. Underneath the glacier, where glacier ice meets the ground, large amounts of rock and soil are ground up by the tremendous weight of the glacier.		Photo: This hanging glacier above Lyman Lake in Washington State may look simply like a mass of snow, but the crevasses are evidence that it really is a glacier. (United States Forest Service photograph at the World Data Center for Glaciology, University of Colorado, Boulder.)
		Other common glacial features are moraines, created when the glacier pushes or carries along rocky debris as it moves. These long, dark bands of debris are visible on top and along the edges of glaciers. Medial moraines run down the middle of a glacier, lateral moraines along the sides, and terminal moraines are found at the terminus, or snout, of a glacier. Sometimes one glacier flows into another, creating combined wider morraines as shown in the photo to the left.		Photo: Barnard Glacier shows several medial moraines. In this case, the widest medial moraines occur where additional glaciers flow into Barnard Glacier. (Austin S. Post photograph at the World Data Center for Glaciology, Univesity of Colorado, Boulder.)

Where are glaciers located?

Most of the world’s glacial ice is found in Antarctica and Greenland, but glaciers are found on nearly every continent, even Africa. Because certain climatic and geographic conditions must be present for glaciers to exist, they are most commonly found above snow line: regions of high snowfall in winter, and cool temperatures in summer. This condition allows more snow to accumulate on the glacier in the winter than will melt from it in the summer. This is why most glaciers are found either in mountainous areas or the polar regions. However, snow line occurs at different altitudes: in Washington State the snow line is around 1600 meters (or 5,500 feet), while in Africa it is over 5100 meters, and in Antarctica it is at sea level. The amount of snowfall a glacier can transform into ice is very important to its survival, which is why even a cold region like Siberia experiences almost no glaciation–there is not enough snowfall.

Approximate Worldwide Area Covered by Glaciers (square kilometers)
Antarctica		11,965,000 (without iceshelves and ice rises)	Total glacier coverage is nearly 15,000,000 square kilometers, or a little less than the total area of the South American continent. (The numbers listed do not include smaller glaciated polar islands or other small glaciated areas, which is why they do not add up to 15,000,000. For more in depth numbers, visit Areal Extent of Present-day Glaciers, a publication of the United States Geological Survey.)
Greenland		1,784,000
Canada		200,000
Central Asia		109,000
Russia		82,000
United States		75,000 (including Alaska)
China and Tibet		33,000
South America		25,000
Iceland		11,260
Scandinavia		2,909
Alps		2,900
New Zealand		1,159
Mexico		11
Indonesia		7.5
Africa		10

What types of glaciers are there?

There are:

Ice Sheets Ice Shelves Ice Caps Ice Streams/Outlet Glaciers Icefields Mountain Glaciers

Valley Glaciers Piedmont Glaciers Cirque Glaciers Hanging Glaciers Tidewater Glaciers

Ice Sheets

Found only in Antarctica and Greenland, ice sheets are enormous continental masses of glacial ice and snow expanding over 50,000 square kilometers. The ice sheet on Antarctica is over 4200 meters thick in some areas, covering nearly all of the land features except the Transantarctic Mountains, which protrude above the ice. Another example is the Greenland ice sheet.

Ice Shelves

Ice shelves occur when ice sheets extend over the sea, and float on the water. In thickness they range from a few hundred meters to over 1000 meters. Ice shelves surround most of the Antarctic continent. Retreating ice shelves may provide indications of climate change. For example, the Larsen Ice Shelf has been retreating since the spring of 1998. Check out some of the remotely sensed satellite images scientists used to monitor the ice shelf breakup.

The Larsen Ice Shelf in Antarctica, March 21, 1998. Taken at the beginning of the antarctic winter, the ice shelf is clearly visible. Notice that sea ice is forming over the ocean to the right the ice shelf. (NSIDC AVHRR stretched thermal-band Image, March 21, 1998.)

Ice Caps

Ice caps are miniature ice sheets, covering less than 50,000 square kilometers. They form primarily in polar and sub-polar regions that are relatively flat and high in elevation. To really see the difference between an ice cap and an ice sheet, compare Iceland and Greenland on a globe or world map. The much smaller mass of ice on Iceland is an ice cap.

Ice Streams and Outlet Glaciers

Ice streams are channelized glaciers that flow more rapidly than the surrounding body of ice. For instance, the Antarctic ice sheet has many ice streams flowing outward.

Icefields

Ice fields are similar to ice caps, except that their flow is influenced by the underlying topography, and they are typically smaller than ice caps.

Kalstenius Ice Field, located on Ellesmere Island, Canada, shows vast stretches of ice. The icefield produces multiple outlet glaciers that flow into a larger valley glacier. The glacier in this photograph is three miles wide. (Royal Canadian Air Force photograph at the World Data Center for Glaciology, University of Colorado, Boulder.)

Mountain Glaciers

These glaciers develop in high mountainous regions, often flowing out of icefields that span several peaks or even a mountain range. The largest mountain glaciers are found in Arctic Canada, Alaska, the Andes in South America, the Himalayas in Asia, and on Antarctica.

In this undated photograph, Variegated Glacier winds through the Saint Elias Mountains in Alaska, terminating near Yakutat Bay. An ice field is visible in the upper left hand corner of the photograph. (Unattributed photograph at the World Data Center for Glaciology, University of Colorado, Boulder.)

Valley Glaciers

Commonly originating from mountain glaciers or ice fields, these glaciers spill down valleys, looking much like giant tongues. Valley glaciers may be very long, often flowing down beyond the snow line, sometimes reaching sea level.

Piedmont Glaciers

Piedmont glaciers occur when steep valley glaciers spill into relatively flat plains, where they spread out into bulb-like lobes. The Malaspina Glacier in Alaska is one of the most famous examples of this type of glacier, and is the largest piedmont glacier in the world. Spilling out of the Seward Ice Field, Malaspina Glacier covers over 5,000 square kilometers as it spreads across the coastal plain.

The massive lobe of Malaspina Glacier is clearly visible in this photograph taken from a Space Shuttle flight in 1989. Agassiz Glacier is to the left of Malaspina Glacier, and towards the top of the photograph Seward Ice Field is just visible. (Photograph courtesy of SPACE.com and NASA.)

Cirque Glaciers

Cirque Glaciers are named for the bowl-like hollows they occupy, which are called cirques. Typically, they are found high on mountainsides and tend to be wide rather than long.

Hanging Glaciers

Also called ice aprons, these glaciers cling to steep mountainsides. Like cirque glaciers, they are wider than they are long. Hanging glaciers are common in the Alps, where they often cause avalanches due to the steep inclines they occupy.

Tidewater Glaciers

As the name implies, these are valley glaciers that flow far enough to reach out into the sea. Tidewater glaciers are responsible for calving numerous small icebergs, while not as imposing as Antarctic icebergs, can still pose problems for shipping lanes.

Lamplugh Glacier, in Glacier Bay, Alaska, shows the snout of a typical tidewater glacier. Because the surface of the ice is heavily crevassed and jagged, small bits of ice have broken off, seen here floating in the water. (AGS collection, 1941, at the World Data Center for Glaciology, Boulder)

How do glaciers affect the land?

Glaciers not only transport material as they move, but they also sculpt and carve away the land beneath them. A glacier’s weight, combined with its gradual movement, can drastically reshape the landscape. Over hundreds or even thousands of years, the ice totally changes the landscape. The ice erodes the land surface and carries the broken rocks and soil debris far from their original places, resulting in some interesting glacial landforms.

Glacial Erosion

Common all over the world, glaciated valleys are probably the most readily visible glacial landform. Similar to fjords, they are trough-shaped, often with steep vertical cliffs where entire mountainsides were removed by glacial action. One of the most striking examples of glaciated valleys can be seen in Yosemite National Park, where glaciers literally sheared away mountainsides, creating deep valleys with vertical walls.

Glacier National Park, in Montana, U.S.A., also shows a variety of glaciated valleys. Here, part of the mountain has been cut away by a glacier. (U.S. Air Force collection at the World Data Center for Glaciology, Boulder)

Fjords, such as those in Norway, are long, narrow coastal valleys that were originally carved out by glaciers. Steep sides and rounded bottoms give them a trough-like appearance. Because of glacial erosion on the below sea level land surface, when glaciers finally disappear, sea water covers the valley floor.

The famous Matterhorn in Switzerland displays three types of glacial erosion:

Cirques are created when glaciers erode backwards, into the mountainside, creating rounded hollows shaped like a shallow bowls.

Aretes are jagged, narrow ridges created where the back walls of two cirque glaciers meet, eroding the ridge on both sides.

Horns, such as the famous Matterhorn in Switzerland, are created when several cirque glaciers erode a mountain until all that is left is a steep, pointed peak with sharp, ridge-like aretes leading up to the top.

The Matterhorn in Switzerland was carved away by glacial erosion. The cirque on this side still contains a glacier, and to the far left, a hanging glacier clings precariously to the side of the peak. Notice the crevasses on each of the glaciers. This photograph dates from 1894. (World Data Center for Glaciology, Boulder)

Glacial Landforms

Fjords, glaciated valleys, and horns are all erosional types of landforms, created when a glacier cuts away at the landscape. Another type of glacial landform is created by deposition, or what a glacier leaves as it retreats or melts away.

An eroded moraine juts above the landscape in the Rhone Valley, Switzerland. Giant boulders stud some of the pinnacles, left behind by a retreating glacier. A small tunnel has been cut through the moraine, seen at the center of the photograph. (H.F. Reid Collection, 1902, at the World Data Center for Glaciology, Boulder)

Till is material that is deposited as glaciers retreat, leaving behind mounds of gravel, small rocks, sand and mud. It is made from the rock and soil ground up beneath the glacier as it moves. Glacial till can form excellent soil for farmland.

Material a glacier picks up or pushes as it moves forms moraines along the surface and sides of the glacier. As a glacier retreats, the ice literally melts away from underneath the moraines, so they leave long, narrow ridges that show where the glacier used to be. Glaciers don’t always leave moraines behind, because sometimes the glacier’s own meltwater carries the material away.

Streams flowing from glaciers often carry some of the rock and soil debris out with them. These streams deposit the debris as they flow. Consequently, after many years, small steep-sided mounds of soil and gravel begin to form adjacent to the glacier, called kames.

Meltwater flows out from under the terminus of Forno Glacier in this photograph from 1899. (H. F. Reid Collection, 1899, at the World Data Center for Glaciology, University of Colorado, Boulder.)

Kettle lakes form when a piece of glacier ice breaks off and becomes buried by glacial till or moraine deposits. Over time the ice melts, leaving a small depression in the land, filled with water. Kettle lakes are usually very small, and are more like ponds than lakes.

Glaciers leave behind anything they pick up along the way, and sometimes this includes huge rocks. Called erratic boulders, these rocks might seem a little out of place, which is true, because glaciers have literally moved them far away from their source before melting away.

<!– leave out until we get copyright permissions

(Fred D. Ayres photography, 1936, at the World Data Center for Glaciology, University of Colorado, Boulder.)

–>Drumlins are long, tear-drop-shaped sedimentary formations. What caused drumlins to form is poorly understood, but scientists believe that they were created subglacially as the ice sheets moved across the landscape during the various ice ages. Theories suggest that drumlins might have been formed as glaciers scraped up sediment from the underlying ground surface, or from erosion or deposition of sediment by glacial meltwater, or some combination of these processes. Because the till, sand and gravel that form drumlins, are deposited and shaped by glacier movement, all drumlins created by a particular glacier face the same direction, running parallel to the glacier’s flow. Often, hundreds to thousand of drumlins are found in one place, looking very much like whalebacks when seen from above.

Do glaciers affect people?

Today, glaciers often are tourist attractions in mountainous areas. But glaciers are also a natural resource, and people all over the world are trying to harness the power of these frozen streams.

Glaciers Provide Drinking Water

People living in the city of La Paz, Bolivia, rely on glacial melting from a nearby ice cap to provide water during the significant dry spells they experience.

Although parts of Japan receive tremendous amounts of snow, there are no glaciers. Because the Japanese must endure frequent droughts, scientists are examining ways to create artificial glaciers that could provide more water for people when the weather is dry.

Glaciers Irrigate Crops

Over a thousand years ago, farmers in Asia knew that dark colors absorb the solar energy. So, they spread dark-colored materials such as soil and ashes over snow to promoted melting, and this is how they watered their crops in the springtime. Chinese and Russian researchers have recently tried something similar by sprinkling coal dust onto glaciers, hoping that the melting will provide water to the drought-stricken countries of India, Afghanistan, and Pakistan. However, the experiment proved to be too costly, and they have abandoned the idea.

In Switzerland’s Rhone Valley, farmers have irrigated their crops for hundreds of years, by channeling meltwater from glaciers to their fields.

Glaciers Help Generate Hydroelectric Power

Scientists and engineers in Norway, Canada, New Zealand and the Alps have worked together to tap into glacial resources, using electricity that has been generated in part by damming glacial meltwater.

Are glaciers dangerous?

Glaciers usually are found in remote mountainous areas. However, some are found near cities or towns and sometimes present a problem for people living close by. On land, lakes formed on top of a glacier during the melt season may cause floods. At the snout (or terminus) of a valley glacier, ice falling from the glacier presents a hazard to hikers below. When ice breaks off over the ocean, an iceberg is formed. Some examples of these hazards are listed below.

Flooding Caused by a Glacier

In Peru in 1941, 6,000 people perished when a glacial lake suddenly burst open, flooding the town of Huaraz below it. Since then, another lake has formed at the base of the glacier, but engineers have created artificial channels to prevent future flooding.

Avalanches from Glaciers

Ice avalanches from glacier snouts have been recorded in the Swiss Alps for centuries, and they still happen despite attempts to prevent them. In 1965, Switzerland was constructing a dam for a hydro-electric plant above the town of Mattmark. Without warning, an enormous mass of ice from the tongue of the nearby Allalingletscher broke off. In mere seconds, the avalanche had rushed down the slopes and buried much of the construction camp, killing 88 workers.

The Threat of Icebergs

Icebergs broken off, or calved, from ice shelves and tidewater glaciers pose a significant threat to sea lanes worldwide. One of the most famous examples is the Titanic, which in April 1912 carried 1,503 passengers to a watery grave after a collision with an iceberg that ripped a 90 meter hole in the ship. Shipping lanes along the coasts of Greenland and Newfoundland are historically iceberg-infested waters.

Icebergs calved by glacial ice continue to present problems even today. Recently, an enormous iceberg, over 80 kilometers long and 40 kilometers wide, broke away from the Larsen Ice Shelf in Antarctica. Because this iceberg may threaten southern shipping routes, it is being carefully observed by satellites and aerial survey.

How do glaciers reflect climate change?

Glacial ice can range in age from several hundred to several hundreds of thousands years, making it valuable for climate research. To see a long-term climate record, an ice core is drilled and extracted from the glacier. Ice cores have been taken from around the world, including Peru, Canada, Greenland, Antarctica, Europe, and Asia. These cores are continuous records providing scientists with information regarding past climate. Scientists analyze various components of cores, particularly trapped air bubbles, which reveal past atmospheric composition, temperature variations, and types of vegetation. Glaciers literally preserve bits of atmosphere from thousands of years ago in these tiny air bubbles. This is how scientists know that there have been several Ice Ages. Past eras can be reconstructed, showing how and why climate changed, and how it might change in the future.

Scientists are also finding that glaciers reveal clues about global warming. How much does our atmosphere naturally warm up between Ice Ages? How does human activity affect climate? Because glaciers are so sensitive to temperature fluctuations accompanying climate change, direct glacier observation may help answer these questions. Since the early twentieth century, with few exceptions, glaciers around the world have been retreating at unprecedented rates. Some scientists attribute this massive glacial retreat to the Industrial Revolution, which began around 1760. In fact, some ice caps, glaciers and even an ice shelf have disappeared altogether in this century. Many more are retreating so rapidly that they may vanish within a matter of decades. Scientists are discovering that production of electricity, along with coal and petroleum use in industry, affects our environment in ways we did not understand before. Within the past 200 years or so, human activity has increased the amount of carbon dioxide and other greenhouse gases released into the atmosphere.

The 1991 discovery of the 5,000 year-old “ice man,” preserved in a glacier in the European Alps, fascinated the world (see National Geographic, June 1 1993, volume 183, number 6, for an article titled “Ice Man” by David Roberts). Tragically, this also means that this glacier is retreating farther now than it has in 5,000 years, and no doubt other glaciers are as well. Scientists, still trying to piece together all of the data they are collecting, want to find out whether human-induced global warming is tipping the delicate balance of the world’s glaciers.

source:http://www-nsidc.colorado.edu/glaciers/questions

Lava Flows and Their Effects

Fluid basalt lava flow, Mauna Loa, Hawai`i

What are Lava Flows? Lava flows are streams of molten rock that pour or ooze from an erupting vent. Lava is erupted during either nonexplosive activity or explosive lava fountains. Lava flows destroy everything in their path, but most move slowly enough that people can move out of the way. The speed at which lava moves across the ground depends on several factors, including (1) type of lava erupted and its viscosity; (2) steepness of the ground over which it travels; (3) whether the lava flows as a broad sheet, through a confined channel, or down a lava tube; and (4) rate of lava production at the vent. Fluid basalt flows can extend tens of kilometers from an erupting vent. The leading edges of basalt flows can travel as fast as 10 km/hour on steep slopes but they typically advance less than 1 km/hour on gentle slopes. But when basalt lava flows are confined within a channel or lava tube on a steep slope, the main body of the flow can reach velocities >30 km/hour. Viscous andesite flows move only a few kilometers per hour and rarely extend more than 8 km from their vents. Viscous dacite and rhyolite flows often form steep-sided mounds called lava domes over an erupting vent. Lava domes often grow by the extrusion of many individual flows >30 m thick over a period of several months or years. Such flows will overlap one another and typically move less than a few meters per hour.

Viscous dacite lava dome, Unzen Volcano, Japan

Effects of Lava Flows

Photograph by J.D. Griggs in 1984 `A`a lava flow moves through an intersection in the Royal Garderns subdivision on the south flank of Kilauea Volcano, Hawai`i.

Everything in the path of an advancing lava flow will be knocked over, surrounded, or buried by lava, or ignited by the extremely hot temperature of lava. When lava erupts beneath a glacier or flows over snow and ice, meltwater from the ice and snow can result in far-reaching lahars. If lava enters a body of water or water enters a lava tube, the water may boil violently and cause an explosive shower of molten spatter over a wide area. Methane gas, produced as lava buries vegetation, can migrate in subsurface voids and explode when heated. Thick viscous lava flows, especially those that build a dome, can collapse to form fast-moving pyroclastic flows.

Lava buries or surrounds everything…	Intense heat of lava melts or burns…	Lava melts snow and ice to form jökulhlaups and lahars…	Collapsing lava flows trigger pyroclastic flows…

Deaths caused directly by lava flows are uncommon because most move slowly enough that people can move out the way easily and flows usually don’t travel far from the vent. Death and injury can result when onlookers approach an advancing lava flow too closely or their retreat is cut off by other flows. Deaths attributed to lava flows are often due to related causes, such as explosions when lava interacts with water, the collapse of an active lava delta, asphyxiation due to accompanying toxic gases, pyroclastic flows from a collapsing dome, and lahars from meltwater.

Other natural phenomena such as hurricanes, tornadoes, tsunami, fires, and earthquakes often destroy buildings, agricultural crops, and homes, but the owner(s) can usually rebuild or repair structures and their businesses in the same location. Lava flows, however, can bury homes and agricultural land under tens of meters of hardened black rock; landmarks and property lines become obscured by a vast, new hummocky landscape. People are rarely able to use land buried by lava flows or sell it for more than a small fraction of its previous worth.

source: http://volcanoes.usgs.gov

ESA Leads Endeavour To Save Earth Science Data

The amount of information being generated about our planet is increasing at an exponential rate, but it must be easily accessible in order to apply it to the global needs relating to the state of the Earth.

GENESI-DR (Ground European Network for Earth Science Interoperations - Digital Repositories), an ESA-led, European Commission (EC)-funded two-year project, is taking the lead in providing reliable, easy, long-term access to Earth Science data via the Internet.

“We shall soon be receiving petabytes of data about our planet from space, so data access will be a major logistical problem. The EC has funded GENESI-DR as a flagship project in Europe to help meet this challenge,” said Prof. Alan O’Neill, Director of the National Centre for Earth Observation at the University of Reading.

GENESI-DR will allow scientists from different Earth Science disciplines located across Europe to locate, access, combine and integrate historical and fresh Earth-related data from space, airbourne and in-situ sensors archived in large distributed repositories.

Currently, information about the state of the Earth, relevant services, analysis results, applications and tools are accessible in a very scattered and uncoordinated way, often through individual initiatives from Earth Observation mission operators, scientific institutes dealing with ground measurements, service companies, data catalogues, etc.

A dedicated infrastructure providing transparent access to all this will support Earth Science communities by allowing them to easily and quickly derive objective information and share knowledge based on all environmentally sensitive domains.

The use of high-speed networks (GÉANT) and the experimentation of new technologies, like BitTorrent, will also contribute to better services for the Earth Science communities.

In order to reach its objectives, the GENESI-DR e-Infrastructure will be validated against user needs for accessing and sharing Earth Science data. Initially, four specific applications in the land, atmosphere and marine domains have been selected, including:

- Near real time orthorectification for agricultural crops monitoring

- Urban area mapping in support of emergency response

- Data assimilation in GlobModel, addressing major environmental and health issues in Europe, with a particular focus on air quality

- SeaDataNet to aid environmental assessments and to forecast the physical state of the oceans in near real time.

- Other applications will complement this during the second half of the project.

“Data assimilation makes use of the diverse observational data now available to us and synthesises them into a coherent picture of the evolving state of the planet - a digital rendition of the real world,” said O’Neill, who is working on GlobModel and GENESI-DR.

“No institution has all the skills in one place, but must be drawn from university and operational institutions distributed across many countries. With this objective in mind for Europe, ESA funded the GlobModel project and GENESI-DR could represent the way to ensure easy access to all necessary data and resources.”

GENESI-DR also aims to develop common approaches to preserve the historical archives and the ability to access the derived user information as both software and hardware transformations occur.

Ensuring access to Earth Science data for future generations is of utmost importance because it allows for the continuity of knowledge generation improvement. For instance, scientists accessing today’s climate change data in 50 years will be able to better understand and detect trends in global warming and apply this knowledge to ongoing natural phenomena.

GENESI-DR will work towards harmonising operations and applying approved standards, policies and interfaces at key Earth Science data repositories. To help with this undertaking, GENESI-DR will establish links with the relevant organisations and programmes such as space agencies, institutional environmental programmes, international Earth Science programmes and standardisation bodies.

From an industry point of view, Stefano Beco, the Innovation and Advanced Applications Group Manager for Elsag Datamat, one of the Directors of the project, said the project’s infrastructure, which is based on state-of-the-art technologies such as Grid, will pave the way for them introducing new services in the Earth Science domain from a scientific and commercial viewpoint.

“We believe that GENESI-DR will push towards an easily accessible ‘virtual repository’, where an extremely large set of valuable scientific information will be available to small and medium enterprises and large companies, providing benefits to different actors, from data providers to service providers to end users,” Beco said.

Source : http://www.terradaily.com/

Russia to be covered with stereo images from Cartosat-1

Russia, March 6 2008 - ScanEx on last Thursday announced about its right to receive 6 000 minutes (100 times more!) of Cartosat-1 data and exclusive right in distribution of acquired data. The contract signed between ScanEx and ANTRIX Corporation Ltd (IRS satellites Operator) in August 2006 provided for 60-minute data transmission to UniScan™ ground stations. Up to 2008 the operational data reception from Cartosat-1 has been carried out by ScanEx R&D Center in Samara (Samara State Aerospace University) and Magadan (Magadan Region Forestry Agency).

Since March 2008 the new agreement comes into force under which 5 ground stations in Khanty-Mansiysk, Irkutsk, Yakutsk, Magadan and Samara will be receiving data from the satellite for the maximum possible coverage of the Russian territory with stereo images.

Also the new agreement provides similar license terms for the reception and exclusive right in distribution of data from another IRS series satellite - Resourcesat-1 (IRS-P6). Resourcesat-1 data archive has been replenished by ScanEx Center since 2006.

Source:www.gisdevelopment.net