Category The World Around us

Mountain ranges make up some of the world’s most impressive landscapes. Like earthquakes and volcanoes, they are formed as a consequence of the activity of the Earth’s tectonic plates. Where the plates push up against one another, the Earth’s crust buckles and folds, resulting in ranges of Rocky Mountains. Volcanoes also make up some of the world’s greatest mountains.

There are a few ways that mountains can form. One thing these methods have in common is that they all take millions of years!

Most mountains formed from Earth’s tectonic plates smashing together. Below the ground, Earth’s crust is made up of multiple tectonic plates. They’ve been moving around since the beginning of time. And they still move today as a result of geologic activity below the surface. On average, these plates move at a rate of about one to two inches each year.

When two tectonic plates come together, their edges can crumple. Think of what happens to an aluminum can when you crush it. It’s a bit like that! The result of these tectonic plates crumpling is huge slabs of rock being pushed up into the air. What are those called? Mountains, of course! Specifically, these are called “fold mountains.” 

For example, the tectonic plates that lie underneath India and Asia crashed into each other over 25 million years ago. What happened? The Himalayas, including Mount Everest, formed. And they’re still pushing against each other. That means the Himalayas are still growing even today!

Sometimes, instead of crashing together, two tectonic plates grind against each other. Occasionally, this results in one plate lifting up and tilting over. The result? A fault-block mountain range! One example is the Sierra Nevada mountain range in California.

Other times, a unique type of mountain is made when one plate is pushed below the other, pushing magma to the surface. This is how volcanoes, like Mount Fuji, are made. Volcanic activity below Earth’s surface can also result in new mountains when magma is pushed up toward the surface. When that happens, it cools and forms hard rock. The result is dome mountains. 

Mountains can also form by way of erosion. In an area with a high plateau, rivers and streams can carve away stone in the form of deep channels. Over millions of years, what is left is a mountain between deep river valleys!

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Scientists who study glaciers and polar ice are called glaciologists. There are permanent research stations based in Polar Regions, manned by glaciologists who can discover a great deal about the Earth. Working in laboratories dug out of the ice, they investigate layers of ice that contain gases and substances from climatic conditions of the past. Ice cores are also drilled from the ice and taken back to laboratories for detailed testing.

Earth has two polar regions – the Arctic and the Antarctic – and each is considerably larger than the lower 48 United States.  The most distinctive features of both polar regions are cold climate and abundant snow and ice, caused by the extreme annual variation of sunlight.  At the North and South Poles, the sun is below the horizon for six consecutive months, then above the horizon for the next six months.  Poleward of the Arctic and Antarctic Circles (currently approximately 66º 34’ North and South) there is at least one 24-hour period each year when the sun is continuously above the horizon, and one when it is continuously below it.  These circles are sometimes used to define the boundaries of the polar regions. Other definitions are poleward of treeline and poleward of the line where the average surface air temperature exceeds 10º C in the warmest month of the year.

The central Arctic is an ocean with depths exceeding 4000 meters, topped by sea-ice (frozen seawater) of average thickness 3 meters.  The sea-ice moves continually in response to winds and ocean currents, with typical speeds of 5-10 km per day.  Tundra, a treeless land of low growing vegetation, covers the northern fringes of the surrounding continents.

The central Antarctic is a continent, covered by a massive sheet of glacial ice (formed by accumulation of snowfall) of average thickness 2000 meters.  The glacial ice moves slowly downhill in response to gravity, with horizontal speed on the order of 10m per year.  The vast Southern Ocean surrounds the continent, and supports a canopy of sea-ice thinner on average than its Arctic counterpart.

People settled in the Arctic thousands of years ago, and when explorers from lower latitude reached the Arctic, they found established cultures based on subsistence hunting.  In the Antarctic the human presence is limited primarily to tourists and scientists who stay for a season or a year.

The polar regions are home to a surprising variety of animals and plants.  Each species has adapted to the prolonged periods of sunlight and darkness, the low temperature, and the snow and ice.  In the central Arctic, polar bears and Arctic foxes roam the surface of the pack ice.  In Antarctica penguins inhabit the perimeter of the continent, feeding in the coastal waters and rearing their young on the ice surface.  Marine mammals such as whales and seals abound in the Arctic and the Antarctic, though there are differences of species, for example the walrus lives only in the Arctic, while the leopard seal is an Antarctic resident.  Caribou, musk ox, grizzly bears and lemmings range over the Arctic tundra.

Polar science is a broad term encompassing the scientific study of any aspect of the polar regions.  Science treats phenomena as consequences of general laws, which may be refuted or not refuted by following the scientific method of observation, hypothesis, experiment and measurement.  Polar science has its disciplines, sub-disciplines and inter-disciplines, e.g. physics, chemistry, biology, anthropology, sociology, oceanography, meteorology, biogeochemistry, botany, zoology, and ecology.  A large fraction of polar science fits well under the heading “environmental science”, which sometimes is taken to mean the study of everything non-human that interacts with humans.  Thus defined, polar science encompasses much.  It applies equally to the zoologist fastening a tracking device to a polar bear on the Arctic pack ice, as to the theoretical physicist working on mathematical expressions of thermodynamic principles to predict how a gas migrates through the glacial ice sheet on Antarctica.  The last 30 years or so have seen a notable increase in research concerned with long term, progressive changes in the polar regions.  This increase has been spurred by theories of climate change as a response to increased concentrations of greenhouse gases in the atmosphere, and by observations of large scale environmental change, especially in the Arctic.

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When the temperature of the sea dips below —1.9°C (28°F), it can freeze. This happens off the Antarctic coast and other glaciated regions. The whole of the North Pole is in fact frozen sea that is never more than a few metres thick. Sea ice is often referred to as pack ice.

If the temperature is cold enough, ocean water does freeze. The polar ice cap at earth’s North Pole is a giant slab of frozen ocean water. At earth’s South Pole, the land mass constituting Antarctica complicates the situation, so most of the ice there is compacted snow. Over cold regions such as Antarctica, Greenland, and Canada, the fresh water in the air freezes to snow and falls onto the land without a melting season to get rid of it. Over time, this snow builds up and compacts into an ice mass known as a glacier. Gravity slowly pulls the glacier downhill until it reaches out onto the ocean, forming an ice shelf. The ocean-bound edge of the ice shelf slowly crumbles into icebergs which float off on their own path. For this reason, glaciers, ice shelves, and icebergs are all thick sheets of frozen fresh water and not frozen ocean water. In contrast, when ocean water freezes, it forms a thin flat layer known as sea ice or pack ice. Sea ice has long been the enemy of ships seeking an open route through cold waters, but modern ice breaker ships have no problem breaking a path through the fields of frozen ocean.

Despite the fact that the oceans do freeze when the temperature is cold enough, ocean water does indeed stay liquid under much colder weather than one would first expect. For instance, go to the beach on a winter day and you may be surprised to find that the ocean is still liquid despite the snow and ice on the ground being frozen. There are four main factors that keep the ocean in a liquid state much more than may be expected, as described in the textbook Essentials of Oceanography by Tom Garrison.

Salt
The high concentration of salt in ocean water lowers its freezing point from 32° F (0° C) to 28° F (-2° C). As a result, the ambient temperature must reach a lower point in order to freeze the ocean than to freeze freshwater lakes. This freezing-point depression effect is the same reason we throw salt on icy sidewalks in the winter. The salt lowers the freezing point of the ice below the ambient temperature and it melts. Note that if the ambient temperature is lower than 28° F (-2° C), the ocean water would be ice if this were the only effect involved. Such is not the case, so there must be other effects involved.

Ocean currents

The gravitational pull of the moon, earth’s spinning motion, and thermal convection combine to create large-scale flows of ocean water known as ocean currents. This constant motion of the ocean water helps keep the water molecules from freezing into the somewhat stationary state of ice crystals. More significantly, the ocean currents continuously pump warm water from the equatorial regions to the colder ocean regions.

High volume

The larger the volume of water, the more heat has to be removed in order to freeze it. A teaspoon of water placed in the freezer will become completely solid long before a gallon jug of water. More accurately, it is the surface-area to volume ratio for a given external temperature that determines the rate of heat loss and therefore the speed of freezing. Because the heat must be lost through its surface, a small shallow puddle with a large surface will freeze quicker than a deep lake. The immense volume and depth of the oceans keeps them from freezing too quickly, thereby allowing the heating mechanisms to have a larger effect.

Earth’s internal heating

As miners are well aware, the earth gets hotter and not colder as you dig straight down, despite the fact that you are getting farther away from the warm sunlight. The reason for this is that the earth has its own internal heat source which is driven primarily by the nuclear decay of elements inside earth’s mantle. The earth’s internal heat is most evident when lava flows and hot springs poke through the surface. Because earth’s insulating crust is much thinner under the oceans than under the continents, most of the earth’s internal heat escapes into the oceans. Although the temperature of the air at an ocean’s surface may be freezing, the temperature of the water deep in the ocean is significantly warmer due to internal heating.

This combination of salt, ocean currents, high volume, and internal heating keeps most of the ocean in liquid form even during cold winters.

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An ice cap is a glacier, a thick layer of ice and snow, that covers fewer than 50,000 square kilometers (19,000 square miles). Glacial ice covering more than 50,000 square kilometers (19,000 square miles) is called an ice sheet.

An interconnected series of ice caps and glaciers is called an ice field. Ice caps and ice fields are often punctuated by nunataks. Nunataks are areas where just the summits of mountains penetrate the ice.

Ice caps form like other glaciers. Snow accumulates year after year, then melts. The slightly melted snow gets harder and compresses. It slowly changes texture from fluffy powder to a block of hard, round ice pellets. New snow falls and buries the grainy snow. The hard snow underneath gets even denser. It is known as firn.

As years go by, layers of firn build on top of each other. When the ice grows thick enough—about 50 meters (165 feet)—the firn grains fuse into a huge mass of solid ice. At this point, the glacier begins to move under its own weight.

Ice caps tend to be slightly dome-shaped and spread out from their center. They behave plastically, or like a liquid. An ice sheet flows, oozes, and slides over uneven surfaces until it covers everything in its path, including entire valleys, mountains, and plains. Ice caps and ice fields exist all over the world. Ice caps in high-latitude regions are often called polar ice caps. Polar ice caps are made of different materials on different planets. Earth’s polar ice caps are mostly water-based ice. On Mars, polar ice caps are a combination of water ice and solid carbon dioxide.

Many indigenous people have adapted to life around ice caps. The Yupik people of Siberia live in coastal communities along the Chukchi Peninsula, Russia, and St. Lawrence Island, in the U.S. state of Alaska. They rely primarily on marine life to supply food and material goods, however. Seaweeds, walruses, bowhead whales, and fish provide food staples as well as material for dwellings and transportation such as sleds and kayaks.

Northern Europe is home to many ice caps. Vatnajökull, Iceland, is an ice cap that covers more than 8% of the island nation. Austfonna, in the Svalbard archipelago of Norway, is the largest of many ice caps in Scandinavia. The largest ice cap in the world is probably the Severny Island ice cap, part of the Novaya Zemlya archipelago in the Russian Arctic.

Ice caps and ice fields are found far beyond polar regions, however. Mountain ranges, such as the Himalayas, Rockies, Andes, and the Southern Alps of New Zealand are all home to many ice caps and ice fields.

Mount Kilimanjaro, Tanzania, the tallest mountain in Africa, used to have enormous ice caps on its summit. Today, the Furtwangler glacier is the mountain’s only remaining ice cap, at 60,000 square kilometers (23,166 square miles). The Furtwangler glacier is melting at a very rapid pace, however, and Africa may lose its only remaining ice cap.

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