Lakes, Revised Edition

Jeanne Hanson, Erik Hanson

Description

Both a scientific tour and a journey through time, this intriguing, eBook profiles 10 of the world's most exciting lakes. From the Caspian Sea, a giant salt water lake; to Lake Eyre, the lake that vanishes; to the sub-Arctic Great Slave Lake, the story of each lake unfolds with a look at its origins, how it has changed over time, and why. Featured lakes are found in the Middle East, the United States, Russia, South America, Europe, Australia, and Canada. Eye-catching images and illustrations complement the lively text.

Sujets

• Science de la Terre
• Science
• Nature
• Volume
• Water
• Lake
• Global
• Climate
• Geology
• Environment
• Sciences et techniques
• Young Adult Nonfiction
• Earth Sicences

Informations

• Publié par: Infobase Publishing
• Date de parution: 01 juin 2019
• Nombre de lectures: 0
• EAN13: 9781438182513
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Lakes, Revised Edition
Copyright © 2019 by Jeanne K. Hanson
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For more information, contact:
Chelsea House An imprint of Infobase 132 West 31st Street New York NY 10001
ISBN 978-1-4381-8251-3
You can find Chelsea House on the World Wide Web at http://www.infobase.com
Contents Chapters Lakes Caspian Sea Aral Sea Lake Superior Lake Baikal Lake Titicaca Lake V nern Lake Eyre Crater Lake Great Salt Lake Great Slave Lake Subglacial Lakes Conclusion: Lakes Support Materials Glossary Index
Chapters
Lakes

Viewed from space, our planet is blue and green, but mostly blue. More than 71 percent of the surface of the Earth is water, about 36 million cubic miles (150 km 3 ) of it. Almost all of this—around 97 percent—lies in the oceans as salt water. The remaining three percent is freshwater, composed of glaciers and ice caps (68.7 percent), groundwater (30.1 percent), and surface and other freshwater (1.2 percent). This last category includes ground ice and permafrost, marshes, rivers, and the lakes of the world. 
Freshwater is rare, so rare across the planet that it could be considered blue gold. Without it, life on this planet would not exist. So it is useful to learn about lakes, beginning with a glimpse at the "big picture," the origin of this beautiful and important landform.
Lakes represent only a small amount of Earth’s water: just over one percent. Yet they hold about one-fifth of the planet’s supply of surface freshwater, the majority of which is locked up in glaciers, ice caps, and snow. Freshwater lakes contain more than 98 percent of Earth's usable surface water.
It has been estimated that there are some two million lakes around the world. They come in all shapes and sizes and vary in temperature, salinity, and other factors. Small lakes can be called ponds, and very big lakes may be called seas. When a lake is called a sea, it is because it used to be connected to a prehistoric ocean or sea but is now landlocked. This kind of sea is often considered to be a hypersaline lake. The Dead Sea and the Caspian Sea are examples of this.  The volume of water a lake can hold depends on its depth and surface area. The Caspian Sea is the largest lake in the world by surface area, bordering five countries including Russia and Iran. The deepest lake in the world is Lake Baikal in Siberia, plunging over a mile deep in some areas.
Earth's Changing Landscape
Though a lake may look as though it has existed forever, reflecting the sky and clouds in all their tones and shapes, this is not the case. Earth is an unquiet planet, constantly being shaped in four main ways, naturally and slowly. The first is through the slow movements of massive slabs of rock, known as tectonic plates. Over time, these thick pieces of the planet's crust have moved across Earth's surface, gradually shifting the landmasses, and the lakes within them, like a giant 3-D puzzle.
Climate change over the ages is the second major force to shape the face of the planet and the lakes upon it. It causes glaciers to thicken and shove the land, then melt in immense volumes; rivers to rush fast enough over eons to sweep away hills and block valleys; and frost to crack the rocks that make up the mountains until even the mountains tumble down. Perhaps amazingly, most of the major lakes of the world owe their existence to glaciers and their aftermath.
The third natural "engine" of our planet is tectonic/igneous activity, as exemplified by earthquakes and volcanoes. They crack, push, and pile up the land, or breathe out heat from deep underground that melts rock. Lakes can form in the shapes that earthquakes and volcanoes create in the landscape. For example, a volcanic crater may fill with rain or melted snow when a volcano becomes inactive. One of the deepest lakes in the world, Crater Lake in Oregon, was formed this way. 
The fourth great shape-shifter, erosion, is actually the most significant of these forces of natural change, for the planet as a whole—and the trickiest. Its work often covers up evidence of the other three forces. Erosion can push up enough soil to make a river slide aside, raise hills that change where the snowmelt flows, and fill in valleys with sediments. All of these geologic events set the stage for the creation, change, and elimination of lakes.
Why?
The first and best questions about the natural world are always the whys and the hows. Why did a particular lake form where it did and how long ago? Why has it filled with water? Why is it changing, and what did it look like in the past? Why is one lake so much saltier than another? What is its water chemistry, its biological activity? How do heat, the shape of the lake's basin, light, and the water's inflow and outflow affect the lake? How does a lake "turn over" in the spring and fall? How do changes in its oxygen, nitrogen, and other chemical levels change a lake? How is human activity altering the lake? Questions like these can be answered by the science of geology: the study of Earth across time. Lakes are part of its focus. 
Lake Formation
Lakes begin to form in ten main ways, as described below, with some of these more common than others. The first, tectonic forces, can indeed form lakes, as slabs of rock are lifted up or made to slump, creating a new basin where water can collect. Secondly, volcanic forces create lakes, as lava erupts then collapses into a new basin or flows out to dam a river. Landslides, a third mechanism, can also form bodies of water, when a flood or earthquake moves enough rocky soil to dam a river. Usually this material is not as dense as rock (unless giant boulders are involved) and the dam may wash away in a few weeks or months, making this kind of lake relatively short-lived. 
Glaciers, a fourth method of lake formation, have been, and are, very significant on our planet, especially in the Pleistocene epoch which began about two million years ago. These ice monsters pressed the land down and scooped it out on a giant scale, creating the basins we now know as the Great Lakes as well as many other lakes, large and small. Glaciers acted just as powerfully when they melted. Even the Great Salt Lake began long ago with glacial meltwater. 
Less common methods of lake formation—by solution, river, wind, shoreline change, organic activity, and by deliberate action—are also important. One type of lake, a "solution lake," can form when groundwater or surface water dissolves rock, usually limestone, creating a small basin. Rivers also can create lakes, by blocking a valley or changing their own course to fill a lowlands, for example. Wind forms lake basins, too, by piling up sand and gravel in which water can collect. (These lakes, though, are usually short-lived.) Shoreline changes also create lakes, when part of a larger lake or ocean becomes cut off from its main body of water. Organic activity can even make lakes, especially when a great many plants die and form a dam behind which water collects; this is more in common in the tropics than in the temperate zones of the planet, and these lakes are usually not long-lived. The last method, lake formation by deliberate action of humans (with, believe it or not, the occasional contribution by only one other animal, the beaver) is increasingly common. This kind of activity can create reservoirs, or decorative artificial lakes, or forest pools. People are such champion land movers that our efforts displace many tons of soil and rock each year in house construction, mining, and highway building alone; some of this creates new humanmade lakes.
Of the natural methods of lake formation, only three create the larger, more varied, longer-lived lakes: the tectonic forces, the volcanic forces, and the glaciers. These three earth forces are so powerful that it is estimated that the tectonic forces alone shove up about 14 billion tons of rock each year across the planet, forming mountains and cracking land in half across hundreds of miles to create both rifts and basins. Volcanoes worldwide raise about 30 billion tons of rock up from the ocean floor to make land in new places each year and explode on land to create caldera for lakes. And glaciers, the most significant force in lake creation of all, push about 4.3 billion tons of land around annually, even now. This effect is unimaginably less than what they accomplished in their most recent heyday just a few thousand years ago, when many lakes were made. A planet without these three energetic, dynamic forces would not have seen the creation of very many lakes. Earth will reward all the curiosity one can summon to the understanding of these major engines of change.
A Lake: How Much Water?
Once a lake forms, it develops a "water economy," a balance of some kind in its inflow/outflow "budget." This involves several key factors. First, the inflow. Lakes receive their water from precipitation (rain and snowmelt), from ground flow (via runoff, rivers, and the like), and from groundwater seeping in. The pattern of inflow changes with both season and climate. It is also affected by the shape of the lake's basin, the nature of the runoff, the rivers, and groundwater, and by the lake's location on the planet. The position of the lake with regard to the ocean makes a difference, too, since lakes closer to an ocean receive less rainfall; it rains more over land than over the ocean worldwide, and more water evaporates from the ocean than from the land.
The outflow of water from a lake occurs in several ways. Evaporation and transpiration (plants consuming water) are key. Important also are flow over the surface (a river may draw water away from a lake) and seepage of water into the land's groundwater (though la