My Science School

Icebergs are formed from freshwater ice brought to the sea by glaciers, or when chunks are broken off an ice cap due to the effect of the tide and waves. This effect is known as calving. Icebergs contain large amounts of rock fragments that make them heavy, and they sit low in the sea. Once an iceberg has broken off, its movement depends upon the wind and sea currents.

Iceberg, floating mass of freshwater ice that has broken from the seaward end of either a glacier or an ice shelf. Icebergs are found in the oceans surrounding Antarctica, in the seas of the Arctic and subarctic, in Arctic fjords, and in lakes fed by glaciers.

Icebergs of the Antarctic calve from floating ice shelves and are a magnificent sight, forming huge, flat “tabular” structures. A typical newly calved iceberg of this type has a diameter that ranges from several kilometres to tens of kilometres, a thickness of 200–400 metres (660–1,320 feet), and a freeboard, or the height of the “berg” above the waterline, of 30–50 metres (100–160 feet). The mass of a tabular iceberg is typically several billion tons. Floating ice shelves are a continuation of the flowing mass of ice that makes up the continental ice sheet. Floating ice shelves fringe about 30 percent of Antarctica’s coastline, and the transition area where floating ice meets ice that sits directly on bedrock is known as the grounding line. Under the pressure of the ice flowing outward from the centre of the continent, the ice in these shelves moves seaward at 0.3–2.6 km (0.2–1.6 miles) per year. The exposed seaward front of the ice shelf experiences stresses from subshelf currents, tides, and ocean swell in the summer and moving pack ice during the winter. Since the shelf normally possesses cracks and crevasses, it will eventually fracture to yield freely floating icebergs. Some minor ice shelves generate large iceberg volumes because of their rapid velocity; the small Amery Ice Shelf, for instance, produces 31 cubic km (about 7 cubic miles) of icebergs per year as it drains about 12 percent of the east Antarctic Ice Sheet.

Most Arctic icebergs originate from the fast-flowing glaciers that descend from the Greenland Ice Sheet. Many glaciers are funneled through gaps in the chain of coastal mountains. The irregularity of the bedrock and valley wall topography both slows and accelerates the progress of glaciers. These stresses cause crevasses to form, which are then incorporated into the structure of the icebergs. Arctic bergs tend to be smaller and more randomly shaped than Antarctic bergs and also contain inherent planes of weakness, which can easily lead to further fracturing. If their draft exceeds the water depth of the submerged sill at the mouth of the fjord, newly calved bergs may stay trapped for long periods in their fjords of origin. Such an iceberg will change shape, especially in summer as the water in the fjord warms, through the action of differential melt rates occurring at different depths. Such variations in melting can affect iceberg stability and cause the berg to capsize. Examining the profiles of capsized bergs can help researchers detect the variation of summer temperature occurring at different depths within the fjord. In addition, the upper surfaces of capsized bergs may be covered by small scalloped indentations that are by-products of small convection cells that form when ice melts at the ice-water interface.

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After thousands of years, the climate may warm and the glacier melts away. During glaciation, the valley’s shape will have changed from a V-shape to a U-shape. Water can fill the area to form fjords and lakes.

Nearly all scientists agree that we are experiencing a rising temperature of our planet that is caused primarily by our use of fossil fuels (oil, coal and natural gas). Widespread use of these fuels for heat and energy has caused an increase in atmospheric gases that reflect heat back to the surface of the Earth. This warming of the Earth in recent years has caused some of the large bodies of ice and glaciers around the world to begin melting.

As you know, ice is frozen water, and a great deal of water on the Earth is trapped as ocean ice and glaciers. Some of the small glaciers and the ocean ice in the Arctic at the North Pole have begun to melt, but the most important melting is occurring in two really big glaciers covering the island of Greenland in the north and the Antarctic continent at the South Pole. Sea levels are already rising at slow rates, but most predictions are that over the next 85 years (at the end of this century), sea level may increase by 6 or more feet. This means that there are young people like you who are alive today who will see these changes in sea level. If the Greenland and Antarctic glaciers completely melted, sea level would rise more than 200 feet (a 20-story building)! But if this were to happen, it would be in the distant future. 

 

Let’s look at the effects of a 6-foot rise in sea level. First, some inhabited islands in the Pacific Ocean will be underwater; Holland will be at further risk and have to improve its dikes; many coastal cities around the world will have flooding problems; the Florida Everglades will be endangered; and all of these low areas (including New York City) will be in danger of major flooding during storms.

Second, people will have to move from low-lying areas, and their houses and land will lose their value. Third, coastal-area flooding with salt water will spoil some freshwater sources. Fourth, a lot of good agricultural land in low areas will be lost, so there might be a decline in the availability of food. There will be other effects of this warming of the Earth, including droughts, wildfires and other problems as people search for better places to live and move from one area to another.

Scientists agree that we can slow down these climatic changes if we develop better ways to produce energy, such as solar, wind and other forms of energy, and if we reduce our use of coal, oil and gas. Yet the changes that are in place now will continue, so we must plan for a different kind of future. Humans are very smart and should be able to handle these changes on the Earth, so don’t worry too much. Also, don’t spend a lot of money to buy a house on the beach!

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The speed at which glaciers move depends on the steepness of the slope, though they average a speed of around 2m (7ft) a day. It generally takes ice several thousand years to move from - one end of a glacier to the other.

The sheer weight of a thick layer of ice, or the force of gravity on the ice mass, causes glaciers to flow very slowly. Ice is a soft material, in comparison to rock, and is much more easily deformed by this relentless pressure of its own weight. Ice may flow down mountain valleys, fan out across plains, or in some locations, spread out onto 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, and in some cases where the base of the glacier is very cold, the movement at the bottom can be a tiny fraction of the speed of flow at the surface.

Glaciers periodically retreat or advance, depending on the amount of snow accumulation or evaporation or melt that occurs. This retreat and 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, requiring years or decades to have a significant effect. 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. Glaciers that once terminated in the ocean have now receded onto land, retreating far up valleys. Over the past several decades, scientists and researchers have begun to capture data and photographic evidence of this recession over time.

Alternatively, glaciers may surge, racing forward several meters per day for weeks or even months. In 1986, the Hubbard Glacier in Alaska surged at the rate of 10 meters (32 feet) per day across the mouth of Russell Fjord. In only two months, the glacier had dammed water in the fjord and created a lake.

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Glaciation occurs when layers of snow build up in areas over a long period of time. The Layers become compressed and form a mass of ice. Where this happens in the valley areas of mountain range, the layers form into glaciers that, over rime, move slowly down the mountainside. In the Polar Regions, vast frozen areas known as ice caps are formed.

Glaciers are sheets of solidly packed ice and snow that cover large areas of land. They are formed in areas where the general temperature is usually below freezing. This can be near the North and South poles, and also on very high ground, such as large mountains. Snow upon snow on the land becomes compacted and turns into ice. Think about when you make a snowball. You gather fluffy snow in your hands and then press it together. The heat and pressure from your hands make some of the snow melt. When you take a hand away, the liquid water freezes again. The fluffy snow has been compacted into a hard snowball.

Glaciers are formed in a similar way, but on a much larger scale. Sunlight melts some of the snow. Then it freezes during the night, or if the temperature drops. More snow falls onto the surface. Eventually, the weight of snow layers upon snow layers, and the melting and freezing, turns the layers into solid ice. If this ice forms at a high elevation, it starts to slowly slip downhill as an ice “river.” It is called a glacier. On flat land this ice is called an ice cap.

Ice can change the surface of the land. When you look around you, you may not see snow or ice that lasts all year long. That’s what it takes to make a glacier. More snow must fall in a region in winter than melts in summer. When this happens, the amount of snow builds up over time. It’s a lot like money in the bank. If you put more in than you take out, your bank account will grow. Glaciers work the same way. When enough snow builds up in an area, the snow on the bottom becomes compacted by the weight above, changing it into ice. You may have simulated this when making an iceball out of snow or crushed ice.

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The hardness of minerals varies according to the structure of their atoms. A mineral’s hardness is measured using the Mohs scale. Diamond is the hardest mineral and thus has a rating of 10 Mohs.

It is difficult to distinguish between the hardness of a mineral and the ease with which a mineral may be broken. Hardness refers to the ability to scratch the mineral’s surface. However, some hard minerals, like diamond and quartz, break easily if dropped. Hence mineral breakage is different from hardness. Minerals break in two ways: fracture and cleavage. Fracture is irregular breakage. Cleavage is a regular breakage that follows the atomic structure of a mineral. Cleavage results in smooth, planar surfaces. Different minerals may have one, two, three, four, or six cleavages.

Mohs hardness scale is used by geologists to compare the hardness of minerals only. The scale arranges a series of minerals in order of increasing relative hardness, from 1 to 10. Note that this is a relative hardness scale; diamond is actually over four hundred times harder than talc.

PROCEDURE:

1. Draw the Mohs hardness scale on the board. Ask the students which of their lab samples are part of the scale. Ask them if they think the scale is useful. Tell them that the scale works well in a laboratory, but in the field, a geologist would not have all 10 minerals available. Geologists usually use their fingernails and steel knives.
   
    


2. Explain that the Mohs scale does not explain why some minerals are harder than others. Ask students to draw a large person that weighs 250 lbs. and a muscular person that weighs 250 lbs. Ask them if one person is "softer" than the other. One person works out more, and the cells of that body combine tightly, giving him or her a different appearance. The elements of some minerals do the same. The ones that are tightly bound together look different than do ones with looser bonds.

For example, in the illustrations below, (A) shows the atomic structure of carbon in a diamond, and (B) is the carbon arrangement in graphite. (A) is more compact than (B), hence it is harder. As an example, you can tell the students that when Superman squeezes a piece of carbon in his hand, it turns into a diamond. (Superman usually uses coal, which is not the right source of carbon, since the substance should be inorganic to be a real mineral.) If desired, have the students construct Googolplex models of graphite and diamond. Use the directions provided with the Googoplex models. You can also use the Zometool system to construct similar models.

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Pearls are precious stones formed inside shellfish such as oysters, mussels and clams. They form when a piece of grit enters the creature’s shell. The most valuable pearls are those from oysters.

Pearl is a valuable gem known to mankind since ancient times. The pearl, in fact, is of animal origin and produced by certain bivalves of Mollusca. The pearl producing bivalves are marine oysters of the genus Pinctada, though some freshwater bivalves of the genus Unio and Anodonta also produce pearl but of inferior quality and rarely of any use.

The pearl is secreted by the mantle as a protective measure against foreign objects like sand particles, parasites, small larvae or any object of organic and inorganic origin. In fact, as soon as a foreign object, somehow, enters the body of a bivalve in between the shell and mantle, the mantle immediately gets irritated and at once encloses it like a sac. The mantle wall then starts secreting layers of nacre around the foreign object from defence point of view.

Thus, mantle wall secretes continuously several layers of nacre around the foreign object and finally pearl is formed. The value of pearl depends upon its size, quality, etc. Now a day, the pearl producing bivalves are reared and pearls are produced artificially by introducing some foreign objects between the mantle and shell in the different parts of the world; Japan has surpassed all other countries in this field.

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Some minerals are very precious. Diamonds, rubies, emeralds and sapphires are examples of gemstones that are valued for their rarity and beauty. They are difficult to find and expensive to extract from the Earth. Some of them also have particular uses in science and industry that can increase their value.

Gemstones are beautiful pieces of nature that come from the earth that can be made into different types of jewelry. Gemstones are valuable: A lot of time, effort, and information go into mining gemstones. As time goes on, more and more natural gemstones are becoming rarer. As the cost of mining rises, these natural gemstones are harder to come by. Their value is constantly rising due to their scarcity, so one can make a profit from selling them as well.

There is a lot of information that goes into the grading process of all gemstones. First of all, the color of the stone will play a huge part in determining the grade of the stone. The things that matter when it comes to color are the saturation, the hue, the tint, the tone, the grade, the clarity, the brilliance, and several other factors. Other things that are involved in the evaluation of each gemstone include the price per carat, the size, the flaws within the stone, and whether or not the gemstone was mined or produced.

Gemstones are formed hundreds, thousands, and maybe even millions of year ago, so the gemstones that are available now are likely to be the only ones we have in this lifetime. Many mines around the world are empty because we have already gotten out the supply of gemstones available. Although many gemstones can be produced outside of Mother Nature’s gemstone mines, these are not as valuable as natural stones found in the earth. Unfortunately, it costs gemstone miners to do their jobs, and the cost of mining continues to escalate as the supply of the natural gemstones gets smaller and smaller: Miners have to go deeper and deeper into the earth’s surface in order to find these natural gemstones. This will cause gemstones to continue to grow in value as time goes on.

The rarer the stone is, the more it will continue to go up in value. Some of the more rare stones include opals, jade, colored diamonds, star rubies and star sapphires, cat’s eye (asterism) stones, topaz, emeralds, rubies, sapphires, tanzanite, and several others. Because these are rare gemstones, they are slightly more valuable. The larger the stone, the more valuable it will be as well.

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Crystals are formed from minerals that melt or are dissolved in liquids. Crystals in different types of rocks and minerals form one of six different geometric shapes. These shapes were discovered in the 18th century by Abbe Rene Flatly.

A crystal or crystalline solid is a solid material whose constituents, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations.

The scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification. The word crystal is derived from the Ancient Greek word (krustallos), meaning both “ice” and “rock crystal”, from (kruos), “icy cold, frost”.

Most minerals occur naturally as crystals. Every crystal has an orderly, internal pattern of atoms, with a distinctive way of locking new atoms into that pattern to repeat it again and again. The shape of the resulting crystal-such as a cube (like salt) or a six-sided form (like a snowflake)-mirrors the internal arrangement of the atoms. As crystals grow, differences in temperature and chemical composition cause fascinating variations. But students will rarely find in their backyard the perfectly shaped mineral crystals that they see in a museum. This is because in order to readily show their geometric form and flat surfaces, crystals need ideal growing conditions and room to grow. When many different crystals grow near each other, they mesh together to form a conglomerated mass. This is the case with most rocks, such as granite mentioned above, which is made up of many tiny mineral crystals. The museum-quality specimens shown in the images here grew in roomy environments that allowed the geometric shapes to form uninhibited.

The internal arrangement of atoms determines all the minerals’ chemical and physical properties, including color. Light interacts with different atoms to create different colors. Many minerals are colorless in their pure state; however, impurities of the atomic structure cause color. Quartz, for example, is normally colorless, but occurs in a range of colors from pink to brown to the deep purple of amethyst, depending on the number and type of impurities in its structure. In its colorless state, quartz resembles ice. In fact, the root for crystal comes from the Greek word krystallos-ice-because the ancient Greeks believed clear quartz was ice frozen so hard it could not melt.

CRYSTAL SHAPES

CUBIC                             Diamond is an example of a mineral with a cubic structure.

HEXAGONAL                 Beryl has a hexagonal crystal shape.

TETRAGONAL                Zircon has a tetragonal crystal structure.

MONOCLINIC               Gypsum has a monoclinic design.

ORTHOHOMBIC            Sulphur has an orthohombic crystal structure.

TRICLINIC                       Turquoise has crystals in a triclinic shape.

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The rock cycle is the process through which all the Earth's rock is continually changing.

The rock cycle is a process in which rocks are continuously transformed between the three rock types igneous, sedimentary and metamorphic. Rocks of any type can be converted into any other type, or into another rock of the same type, as this diagram illustrates:

Conversion to metamorphic rocks requires conditions of increased temperature and/or increased pressure, conversion to sedimentary rocks occurs via the intermediate stage of sediments, and conversion to igneous rocks occurs via the intermediate stage of magma:

Increased temperature and pressure occurs in subduction zones and in areas where two plates of continental lithosphere collide to produce a mountain range, while increased pressure without increased temperature is produced when sedimentary rocks are deeply buried under more sediments. Sediments are produced when rocks are uplifted, weathered and eroded, and the resulting detrital material deposited in marine or terrestrial basins. If the sediments are buried under further layers of sediment, they can become lithified to produce a sedimentary rock. Magma is produced when rocks are melted. This melting can occur when a lithospheric plate descends into the Earth’s crust at a subduction zone, or when a mid-ocean ridge opens up and produces decompression melting in the athenosphere under the ridge. When the magma solidifies, it becomes an igneous rock.

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The earth’s rocks are divided into three main types. Igneous rock is the original material that makes up the Earth, formed when magma rises to the surface and cools. The planet’s oldest rocks are all of the igneous type. Sedimentary rock is made up of particles of other rock that has been affected by contact with the atmosphere. Erosion caused by water, wind and ice breaks the rock down into tiny particle that are carried away and settle in rivers, lakes and other areas. Over time, the particles compress to form sedimentary rock. Metamorphic rock is formed by the natural effects of heat and pressure changing igneous and sedimentary rock.

The three main types, or classes, of rock are sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed.



Sedimentary

Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock. Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils. Examples of this rock type include conglomerate and limestone.

Metamorphic

Metamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing). The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface. Examples of this rock type include gneiss and marble.

Igneous

Igneous rocks are formed when magma (molten rock deep within the earth) cools and hardens. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes (in this case, it is called lava). When lava cools very quickly, no crystals form and the rock looks shiny and glasslike. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock. Examples of this rock type include basalt and obsidian.

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All rocks are made of various natural substances called minerals. Each mineral has its own chemical make-up, and the different minerals combine together in various ways. Most rocks contain around six different minerals that grow together in a crystal structure.

A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition and the way in which it is formed. Rocks are usually grouped into three main groups: igneous rocks, metamorphic rocks and sedimentary rocks. Rocks form the Earth's outer solid layer, the crust.

Igneous rocks are formed when magma cools in the Earth's crust, or lava cools on the ground surface or the seabed. The metamorphic rocks are formed when existing rocks are subjected to such large pressures and temperatures that they are transformed—something that occurs, for example, when continental plates collide. The sedimentary rocks are formed by diagenesis or lithification of sediments, which in turn are formed by the weathering, transport, and deposition of existing rocks.

The scientific study of rocks is called petrology, which is an essential component of geology. Rocks are composed of grains of minerals, which are homogeneous solids formed from a chemical compound arranged in an orderly manner. The aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which it was formed.

Many rocks contain silica; a compound of silicon and oxygen that forms 74.3% of the Earth's crust. This material forms crystals with other compounds in the rock. The proportion of silica in rocks and minerals is a major factor in determining their names and properties.

Rocks are classified according to characteristics such as mineral and chemical composition, permeability, texture of the constituent particles, and particle size. These physical properties are the result of the processes that formed the rocks. Over the course of time, rocks can transform from one type into another, as described by a geological model called the rock cycle. This transformation produces three general classes of rock: igneous, sedimentary and metamorphic.

Those three classes are subdivided into many groups. There are, however, no hard-and-fast boundaries between allied rocks. By increase or decrease in the proportions of their minerals, they pass through gradations from one to the other; the distinctive structures of one kind of rock may thus be traced gradually merging into those of another. Hence the definitions adopted in rock names simply correspond to selected points in a continuously graduated series.

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Lava differs between volcanoes according to the type of rock it is made from, the gases it contains, and where it erupts. Pahoehoe lava moves quickly and looks rather like coils of rope when it cools. The thicker, lumpier as lava cools into chunky rocks.

Lavas, particularly basaltic ones, come in two primary types: pahoehoe (pronounced 'paw-hoey-hoey") and aa (pronounced "ah-ah"). Both names, like a number of volcanological terms, are of Hawaiian origin. A third type, pillow lava, forms during submarine eruptions. The adjacent picture of a dark pahoehoe flow on a lighter brown aa flow illustrates the difference between the two (photo from Galapagos, Islands Lost in Time by T. De Roy Moore, Viking Press, 1980). The difference in color is in this case is a reflection of age. The older aa in the photo has weathered and the iron in it has oxided somewhat, giving it a reddish appearance (even young aa flows are occasionally slightly brown or reddish, due to the oxidation that occurs during flow). The pahoehoe flow has a comparatively smooth or "ropy" surface. The surface of the aa flow consists of free chunks of very angular pieces of lava. This difference in form reflects flow dynamics.

A forms when lava flows rapidly. Under these circumstances, there is rapid heat loss and a resulting increase in viscosity. When the solid surface crust is torn by differential flow, the underlying lava is unable to move sufficiently rapidly to heal the tear. Bits of the crust are then tumbled in and coated by still liquid lava, forming the chunks. Sometimes the crust breaks in large plates, forming a platy aa. Pahoehoe forms when lava flows more slowly. Under these circumstances, a well-developed skin can form which inhibits heat loss. When a tear in the skin does form, it is readily healed. Both magma discharge rate and the steepness of the slope over which the lava flows affect the flow rate. Thus aa lavas are associated with high discharge rates and steep slopes while pahoehoe flows are associated with lower discharge rates and gentle slopes. The steep slopes of the large western Galapagos volcanos thus generally consist of aa, making ascent very difficult (and occasionally painful!). The less common pahoehoe flows on these volcanos are erupted from vents on the gently sloping apron or the caldera floor. Flows which begin as pahoehoe can convert to aa when a steep slope is encountered.

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When water is heated by volcanic activity, strange and spectacular landscapes are created. Known as hydrothermal areas, they can feature_ steaming hot springs, gurgling pools of mud and jets of water spouting hundreds of feet into the air.

Volcanoes mark vents where molten rock achieves the Earth’s surface -- often in violent fashion. From subtle fissures to skyscraping peaks, these landforms are both destructive and constructive: They can smother terrain and ecosystems with lava, mudflows and ash, but also nourish biological communities with fertile soil and -- significantly -- create new topographic features.

Volcanoes, of course, are themselves landforms: sometimes subtle, sometimes unmistakable and dramatic. The steeply conical silhouette of a composite or stratovolcano -- the classic image of a volcano in most minds -- derives from intermixed layers of viscous lava, ash and other “pyroclastic” materials accumulated over many eruptions and emissions. In sharp contrast, a shield volcano -- such as enormous Mauna Loa and Mauna Kea in Hawaii -- assumes a much gentler slope from easily flowing basaltic lava. Volcanoes may also assume the shape of cinder cones and lava domes. Where weathering and erosion have stripped outer layers from extinct volcanoes, all that may be left on the landscape are resistant remnants of their “throats” and conduits in the form of volcanic necks (or plugs) and dikes. A world-famous example of the former is Shiprock in New Mexico. In the oceans, volcanic seamounts and island arcs are major features marking volatile tectonic margins.

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