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All About Volcanoes for Children: Introduction to Volcanoes for Kids - FreeSchool

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Volcanoes come in many shapes and sizes, ranging from common cinder cone volcanoes that build up from repeated eruptions and lava domes that pile up over volcanic vents to broad shield volcanoes and composite volcanoes. Though they differ in terms of structure and appearance, they all share two things. On the one hand, they are all awesome forces of nature that both terrify and inspire.

On the other, all volcanic activity comes down to the same basic principle. In essence, all eruptions are the result of magma from beneath the Earth being pushed up to the surface where it erupts as lava, ash and rock. But what mechanisms drive this process? What is it exactly that makes molten rock rise from the Earth's interior and explode onto the landscape?

To understand how volcanoes erupt, one first needs to consider the structure of the Earth. At the very top is the lithosphere, the outermost layers of the Earth that consists of the upper mantle and crust. The crust makes up a tiny volume of the Earth, ranging from 10 km in thickness on the ocean floor to a maximum of 100 km in mountainous regions. It is cold and rigid, and composed primarily of silicate rock.

Beneath the crust, the Earth's mantle is divided into sections of varying thickness based on their seismology. These consist of the upper mantle, which extends from a depth of 7 - 35 km (4.3 to 21.7 mi)) to 410 km (250 mi); the transition zone, which ranges from 410-660 km (250-410 mi); the lower mantle, which ranges from 660-2,891 km (410-1,796 mi); and the core-mantle boundary, which is ~200 km (120 mi) thick on average.

In the mantle region, conditions change drastically from the crust. Pressures increase considerably and temperatures can reach up to 1000 °C, which makes the rock viscous enough that it behaves like a liquid. In short, it experiences elastically on time scales of thousands of years or greater. This viscous, molten rock collects into vast chambers beneath the Earth's crust.

Since this magma is less dense than the surrounding rock, it " floats" up to the surface, seeking out cracks and weaknesses in the mantle. When it finally reaches the surface, it explodes from the summit of a volcano. When it's beneath the surface, the molten rock is called magma. When it reaches the surface, it erupts as lava, ash and volcanic rocks.

With each eruption, rocks, lava and ash build up around the volcanic vent. The nature of the eruption depends on the viscosity of the magma. When the lava flows easily, it can travel far and create wide shield volcanoes. When the lava is very thick, it creates a more familiar cone volcano shape (aka. a cinder cone volcano). When the lava is extremely thick, it can build up in the volcano and explode (lava domes).

Another mechanism that drives volcanism is the motion the crust undergoes. To break it down, the lithosphere is divided into several plates, which are constantly in motion atop the mantle. Sometimes the plates collide, pull apart, or slide alongside each other; resulting in convergent boundaries, divergent boundaries, and transform boundaries. This activity is what drives geological activity, which includes earthquakes and volcanoes.

In the case of the former, subduction zones are often the result, where the heavier plate slips under the lighter plate - forming a deep trench. This subduction changes the dense mantle into buoyant magma, which rises through the crust to the Earth's surface. Over millions of years, this rising magma creates a series of active volcanoes known as a volcanic arc.

In short, volcanoes are driven by pressure and heat in the mantle, as well as tectonic activity that leads to volcanic eruptions and geological renewal. The prevalence of volcanic eruptions in certain regions of the world - such as the Pacific Ring of Fire - also has a profound impact on the local climate and geography. For example, such regions are generally mountainous, have rich soil, and periodically experience the formation of new landmasses.

We have written many articles about volcanoes here at Universe Today. Here's What are the Different Types of Volcanoes?, What are the Different Parts of a Volcano?, 10 Interesting Facts About Volcanoes?, What is the Pacific Ring of Fire?, Olympus Mons: The Largest Volcano in the Solar System.

Want more resources on the Earth? Here's a link to NASA's Human Spaceflight page, and here's NASA's Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System - Episode 51: Earth.

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How Do Volcanoes Erupt? - Universe Today

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Volcanoes come in many shapes and sizes, ranging from common cinder cone volcanoes that build up from repeated eruptions and lava domes that pile up over volcanic vents to broad shield volcanoes and composite volcanoes. Though they differ in terms of structure and appearance, they all share two things.

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Home " Minerals " What is a Mineral?

Minerals are the foundation of the construction, manufacturing and agricultural industries.

We Use Minerals Every Day!

Every person uses products made from minerals every day. The salt that we add to our food is the mineral halite. Antacid tablets are made from the mineral calcite. Rubies and sapphires are colored varieties of a mineral named corundum.

It takes many minerals to make something as simple as a wooden pencil. The "lead" is made from graphite and clay minerals, the brass band is made of copper and zinc, and the paint that colors it contains pigments and fillers made from a variety of minerals. A cell phone is made using dozens of different minerals that are sourced from mines throughout the world.

The cars that we drive, the roads that we travel, the buildings that we live in, and the fertilizers used to produce our food are all made using minerals.

In the United States, about three trillion tons of mineral commodities are consumed each year to support the standard of living of 300 million citizens. That is about ten tons of mineral materials consumed for every person, every year.

What are Minerals?

To meet the definition of "mineral" used by most geologists, a substance must meet five requirements:

naturally occurring
inorganic
solid
definite chemical composition
ordered internal structure

" Naturally occurring" means that people did not make it. Steel is not a mineral because it is an alloy produced by people.

" Inorganic" means that the substance is not made by an organism. Wood and pearls are made by organisms and thus are not minerals.

" Solid" means that it is not a liquid or a gas at standard temperature and pressure. Water is not a mineral because it is a liquid.

" Definite chemical composition" means that all occurrences of that mineral have a chemical composition that varies within a specific limited range. For example: the mineral halite (known as " rock salt" when it is mined) has a chemical composition of NaCl. It is made up of an equal number of atoms of sodium and chlorine.

" Ordered internal structure" means that the atoms in a mineral are arranged in a systematic and repeating pattern. The structure of the mineral halite is shown in the illustration on this page. Halite is composed of an equal ratio of sodium and chlorine atoms arranged in a cubic pattern.

Did You Know? Although liquid water is not a mineral, it is a mineral when it freezes. Ice is a naturally occurring, inorganic solid with a definite chemical composition and an ordered internal structure. Learn more.

The Word "Mineral"

The word "mineral" is used in many different ways. Here are some examples:

Geologist's Definition

A formal definition of a mineral, as used by geologists would be: A naturally occurring inorganic solid that has a definite chemical composition, and an ordered internal structure. Geologists are able to identify minerals because they have characteristic physical properties.

Nutritionist's Definition

The word "mineral" also has a nutritional meaning, which is different from the meaning used by geologists.

A nutritionist uses the word mineral when referring to the many inorganic substances that organisms need to grow, repair tissue, metabolize, and carry out other body processes. Mineral nutrients for the human body include: iron, calcium, copper, sulfur, phosphorus, magnesium and many others.

Archaic Use of "Mineral"

An archaic use of the word "mineral" comes from the Linnaean taxonomy in which all things can be assigned to the animal, vegetable, and mineral kingdoms.

Inconsistent Use of "Mineral"

The word "mineral" is also used inconsistently. In mining, anything obtained from the ground and used by man is considered to be a "mineral commodity" or a "mineral material." These include: crushed stone, which is a manufactured product made from crushed rocks; lime, which is a manufactured product made from limestone or marble (both composed of the mineral calcite); coal which is organic; oil and gas which are organic fluids; rocks such as granite that are mixtures of minerals; and, rocks such as obsidian which are mineraloids and do not have a definite composition and ordered internal structure.

2019 United States Mineral Commodity Consumption

Mineral Commodity Million Metric Tons

Crushed Stone

1,600

Sand and Gravel

980

Cement

102

Salt

57.0

Gypsum

42.0

Iron Ore

41.0

Phosphate Rock

25.0

Clays

22.0

Lime

18.0

Sulfur

9.4

Potash

5.4

Soda Ash

5.2

Barite

3.0

Copper

1.8

Lead

1.6

Values above are estimates of apparent mineral commodity consumption from the United States Geological Survey. Many other commodities could be added to this table.

Mineral Commodities in Industry

The construction industry is the largest consumer of mineral commodities. Crushed stone is used for foundations, road base, concrete, and drainage. Sand and gravel are used in concrete and foundations. Clays are used to make cement, bricks, and tile. Iron ore is used to make reinforcing rods, steel beams, nails, and wire. Gypsum is used to make drywall. Dimension stone is used for facing, curbing, flooring, stair treads, and other architectural work. These are just a few of the many uses for these commodities in construction.

In agriculture, phosphate rock and potash are used to make fertilizer. Lime is used as an acid-neutralizing soil treatment. Mineral nutrients are added to animal feed.

The chemical industry uses large amounts of salt, lime, and soda ash. Large amounts of metals, clay, and mineral fillers/extenders are used in manufacturing.

Physical Properties of Minerals

There are approximately 4000 different minerals, and each of those minerals has a unique set of physical properties. These include: color, streak, hardness, luster, diaphaneity, specific gravity, cleavage, fracture, magnetism, solubility, and many more. These physical properties are useful for identifying minerals. However, they are much more important in determining the potential industrial uses of the mineral. Let's consider a few examples.

The mineral talc, when ground into a powder, is perfectly suited for use as a foot powder. It is a soft, slippery powder so it will not cause abrasion. It has the ability to absorb moisture, oils, and odor. It adheres to the skin and produces an astringent effect - yet it washes off easily. No other mineral has a set of physical properties that are as suitable for this purpose.

The mineral halite, when crushed into small grains, is perfectly suited for flavoring food. It has a salty taste that most people find pleasing. It dissolves quickly and easily, allowing its flavor to spread through the food. It is soft, so if some does not dissolve it will not damage your teeth. No other mineral has physical properties that are better suited for this use.

The mineral gold is perfectly suited for use in jewelry. It can be easily shaped into a custom item of jewelry by a craftsperson. It has a pleasing yellow color that most people enjoy. It has a bright luster that does not tarnish. Its high specific gravity gives it a nice "heft" that is preferred by most people over lighter metals. Other metals can be used to make jewelry, but these properties make gold an overwhelming favorite. (Some people might add that gold's rarity and value are two additional properties that make it desirable for jewelry. However, rarity is not a property, and its value is determined by supply and demand.)

Importance of Physical Properties

The primary characteristics of a mineral that determine its physical properties are its composition and the strength of the bonds in its ordered internal structure. Here are some examples:

Galena, a lead sulfide, has a much higher specific gravity than bauxite, an aluminum hydroxide. This difference is because of their composition. Lead is much heavier than aluminum.

Diamond and graphite both consist of pure carbon. Diamond is the hardest natural mineral, and graphite is one of the softest. This difference occurs because of the types of bonds connecting the carbon atoms in their mineral structures. Each carbon atom in diamond is bonded to four other carbon atoms with strong covalent bonds. Graphite has a sheet structure in which atoms within the sheets are bonded to one another with strong covalent bonds, but the bonds between the sheets are weak electrical bonds. When graphite is scratched the weak bonds fail easily, making it a soft mineral.

The gemstones ruby and sapphire are color variations of the mineral corundum. These color differences are caused by composition. When corundum contains trace amounts of chromium, it exhibits the red color of a ruby. However, when it contains trace amounts of iron or titanium, it exhibits the blue color of sapphire. If, at the time of crystallization, enough titanium is present to form tiny crystals of the mineral rutile, a star sapphire may form. This occurs when tiny crystals of rutile align systematically within the crystalline structure of the corundum to give it a silky luster that might produce a "star" that aligns with the primary crystallographic axis (see photo).

Find Other Topics on Geology.com:

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Home " Minerals " What is a Mineral? Minerals are the foundation of the construction, manufacturing and agricultural industries. Every person uses products made from minerals every day. The salt that we add to our food is the mineral halite. Antacid tablets are made from the mineral calcite.

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Home " Rocks

Rocks: Igneous, Metamorphic and Sedimentary

Rocks hold the history of the earth and the materials that will be used to build its future.

Igneous Rocks: Photos, descriptions and facts about intrusive and extrusive igneous rocks.

Metamorphic Rocks: Photos, descriptions and facts about foliated and non-foliated metamorphic rocks.

Sedimentary Rocks: Photos and facts about clastic, chemical and organic sedimentary rocks.

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Rocks: Igneous, Metamorphic and Sedimentary

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Photographs and information for a large collection of igneous, metamorphic and sedimentary rocks. Geology.com

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There are many chemicals in seawater that make it salty. Most of them get there from rivers carrying chemicals dissolved out of rock and soil. The main one is sodium chloride, often just called salt. Most seawater has about 35 g (7 teaspoons) of salt in every 1,000 g (about a litre) of water. This doesn't sound very much, but it would take close to two 6 m shipping containers full of salt to make an Olympic-size swimming pool as salty as the sea.

The commonest way to record salinity is to measure the amount of salt in 1,000 g of water, so it is referred to as 'parts per thousand' or ppt. Most of the ocean has a salinity of between 34 ppt and 36 ppt.

Some properties of water are changed by having salt in it:

Salt makes seawater more dense than freshwater.

Salty water needs to be colder than freshwater before it freezes.

Variation in salinity

The salinity of the ocean varies from place to place, especially at the surface. Much of the ocean has salinity between 34 ppt and 36 ppt, but there are places that tend to be higher or lower.

Places of higher salinity

There are parts of the ocean where hardly any rain falls but warm dry winds cause lots of evaporation. This evaporation removes water - when water vapour rises into the atmosphere, it leaves the salt behind, so the salinity of the seawater increases. This causes the seawater to become denser. You can see on the map that the north and south Atlantic have high salinity - these are areas where there are strong winds and not much rain.

The Mediterranean Sea in Europe has very high salinity - 38 ppt or more. It is almost closed from the main ocean, and there is more evaporation than there is rain or extra freshwater added from rivers.

Places of lower salinity

Some parts of the ocean have lots of rain. The freshwater added at the surface dilutes the seawater, reduces the salinity and so makes the seawater less dense. Seawater can also be less saline near land, where rivers add freshwater.

The ocean around Antarctica has a low salinity of just below 34 ppt, and around the Arctic it is down to 30 ppt in places. Thawing icebergs add freshwater - icebergs that have broken off ice sheets formed over land do not contain salt, and the freezing of seawater into ice floes removes more salt.

The Baltic Sea, almost enclosed by northern Europe and Scandinavia, has a very low salinity of about 10 ppt. This is mainly due to the huge amount of freshwater added from hundreds of rivers.

What happens when salinity changes

The difference between 34 ppt and 36 ppt salinity doesn't sound very much, but it is enough to cause a difference in density. Even slightly denser seawater sinks below less dense water.

However, the effect is greater if the salty water gets cold, as temperature has a greater effect on density than salinity does. A combination of high salinity and low temperature makes seawater so dense that it sinks to the bottom of the ocean and flows across ocean basins as deep, slow currents.

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There are many chemicals in seawater that make it salty. Most of them get there from rivers carrying chemicals dissolved out of rock and soil. The main one is sodium chloride, often just called salt. Most seawater has about 35 g (7 teaspoons) of salt in every 1,000 g (about a litre) of water.

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Maps.com is your guide to exploring our world through maps. Discover trending maps about topics like climate change, social issues, infrastructure, equity, public policy & more.

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Seasons and the Sun: Crash Course Kids 11.1

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Ecosystems and biomes  | Ecology | Khan Academy

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Understanding Latitude and Longitude

Latitude and Longitude: Your Global Address
Every location on earth has a global address. Because the address is in numbers, people can communicate about location no matter what language they might speak. A global address is given as two numbers called coordinates. The two numbers are a location's latitude number and its longitude number ("Lat/Long").

Credit: Illinois State University

Grid Mapping
Using Lat/Long is different from using a street address. Instead of having a specific street address, Lat/Long works with a numbered grid system, like what you see when you look at graph paper. It has horizontal lines and vertical lines that intersect. A location can be mapped or found on a grid system simply by giving two numbers which are the location's horizontal and vertical coordinates; or, to say it another way, the "intersection" where the place is located).

Grid Mapping a Globe:
Latitude and Longitude lines are a grid map system too. But instead of being straight lines on a flat surface, Lat/Long lines encircle the Earth, either as horizontal circles or vertical half circles.

Latitude
Horizontal mapping lines on Earth are lines of latitude. They are known as "parallels" of latitude, because they run parallel to the equator. One simple way to visualize this might be to think about having imaginary horizontal "hula hoops" around the earth, with the biggest hoop around the equator, and then progressively smaller ones stacked above and below it to reach the North and South Poles. (Can you think of other ways to visualize the parallels of Latitude?)

Latitude lines are a numerical way to measure how far north or south of the equator a place is located. The equator is the starting point for measuring latitude--that's why it's marked as 0 degrees latitude. The number of latitude degrees will be larger the further away from the equator the place is located, all the way up to 90 degrees latitude at the poles. Latitude locations are given as __ degrees North or __ degrees South.

Longitude
Vertical mapping lines on Earth are lines of longitude, known as "meridians". One simple way to visualize this might be to think about having hula hoops cut in half, vertically positioned with one end at the North Pole and the other at the South Pole.

Longitude lines are a numerical way to show/measure how far a location is east or west of a universal vertical line called the Prime Meridian. This Prime Meridian line runs vertically, north and south, right over the British Royal Observatory in Greenwich England, from the North Pole to the South Pole. As the vertical starting point for longitude, the Prime Meridian is numbered 0 degrees longitude.

To measure longitude east or west of the Prime Meridian, there are 180 vertical longitude lines east of the Prime Meridian and 180 vertical longitude lines west of the Prime Meridian, so longitude locations are given as __ degrees east or __ degrees west. The 180 degree line is a single vertical line called the International Date Line, and it is directly opposite of the Prime Meridian.

Try it!
The Mystery Class Challenge

Mystery Class is a global game of hide-and-seek. Students track seasonal changes in sunlight to find ten secret sites around the world. More...

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Understanding Latitude and Longitude Latitude and Longitude: Your Global Address Every location on earth has a global address. Because the address is in numbers, people can communicate about location no matter what language they might speak. A global address is given as two numbers called coordinates.

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An ecosystem includes all of the living things in a given area, interacting with each other, and also with their non-living environments. Find out what the levels and organisations of ecosystems are.

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Difference Between Dependent and Independent Variables

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Difference Between Dependent and Independent Variables

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The two main variables in an experiment are the independent and dependent variable.

An independent variable is the variable that is changed or controlled in a scientific experiment to test the effects on the dependent variable.

A dependent variable is the variable being tested and measured in a scientific experiment.

The dependent variable is 'dependent' on the independent variable. As the experimenter changes the independent variable, the effect on the dependent variable is observed and recorded.

Independent and Dependent Variable Example

For example, a scientist wants to see if the brightness of light has any effect on a moth being attracted to the light. The brightness of the light is controlled by the scientist. This would be the independent variable. How the moth reacts to the different light levels (distance to light source) would be the dependent variable.

How to Tell the Variables Apart

The independent and dependent variables may be viewed in terms of cause and effect. If the independent variable is changed, then an effect is seen in the dependent variable. Remember, the values of both variables may change in an experiment and are recorded. The difference is that the value of the independent variable is controlled by the experimenter, while the value of the dependent variable only changes in response to the independent variable.

Remembering Variables With DRYMIX

When results are plotted in graphs, the convention is to use the independent variable as the x-axis and the dependent variable as the y-axis.

The DRY MIX acronym can help keep the variables straight:

D is the dependent variable
R is the responding variable
Y is the axis on which the dependent or responding variable is graphed (the vertical axis)

M is the manipulated variable or the one that is changed in an experiment
I is the independent variable
X is the axis on which the independent or manipulated variable is graphed (the horizontal axis)

Independent vs Dependent Variable Key Takeaways

The independent and dependent variables are the two key variables in a science experiment.

The independent variable is the one the experimenter controls. The dependent variable is the variable that changes in response to the independent variable.

The two variables may be related by cause and effect. If the independent variable changes, then the dependent variable is affected.

Sources

Carlson, Robert. A concrete introduction to real analysis. CRC Press, 2006. p.183.

Dodge, Y. (2003) The Oxford Dictionary of Statistical Terms, OUP. ISBN 0-19-920613-9

Everitt, B. S. (2002). The Cambridge Dictionary of Statistics (2nd ed.). Cambridge UP. ISBN 0-521-81099-X.

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Understand the Difference Between Independent and Dependent Variables

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The two main variables in an experiment are the independent and dependent variable. An independent variable is the variable that is changed or controlled in a scientific experiment to test the effects on the dependent variable. A dependent variable is the variable being tested and measured in a scientific experiment.