Mountains, Revised Edition

Peter Aleshire

Description

This eBook takes readers on a globe-spanning tour of dramatic mountain formations, from block mountains to volcanic sea mountains to high-altitude-landform "sky islands." The direct text invites attention to the complexity of these peaks, their changing nature, and related environmental issues. Enhanced with resources for further investigation, Mountains, Revised Edition also includes a collection of vivid photographs and line illustrations.

Sujets

• Science de la Terre
• Science
• Nature
• Formation
• Mountain
• 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: 9781438182575
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Mountains, Revised Edition
Copyright © 2019 by Peter Aleshire
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 978-1-4381-8257-5
You can find Chelsea House on the World Wide Web at http://www.infobase.com
Contents Chapters Mountains Mount Everest Appalachians Alps Mid-Atlantic Ridge Sierra Nevada Andes Mountains Mauna Kea Mount Saint Helens Mount Kilimanjaro Humphreys Peak Support Materials Glossary Index
Chapters
Mountains 

The rise of mountains baffled early geologists. What could account for these great upthrusts of rock rising miles from the average elevation of the surrounding land? What kept them tall and jagged, despite the steady erosion by wind and water?
Granted, even the tallest mountains on the planet seem puny when viewed from space. The greatest elevation change on the planet occurs over a horizontal distance of just 100 miles (160 km), from the bottom of the deep Atacama Trench off the coast of Chile to the top of the Andes Mountains that run along the coast—more than a 40,000-foot (12,200-m) change in elevation. That nearly 8-mile (13-km) change in such a short space seems impressive to us but is barely a bump on the surface of a planet with a 7,922-mile (12,750-km) diameter. In fact, if you shrank the earth to the size of a billiard ball, the surface would feel just as glossy smooth—with a barely detectable nick here and there. Nonetheless, on a human scale, mountains demand an explanation.
Originally, geologists speculated that the cooling of a once-molten planet could account for both the great ocean basins and the tallest mountain ranges. For generations, geologists struggled to make this theory of mountain building work. They assumed that the rocks of the continents and the rocks of the ocean basins must differ in some way, and that they cooled at different rates. They speculated that as the crust cooled, it contracted—and the surface shriveled like the skin of a dried-out apple. Different rates of cooling based on the chemical compositions of the rock would cause ocean basins to contract more, while the rocks of the continents puckered up to form the ridges of mountain ranges. For many decades, most geologists agreed with this explanation for the rise of mountain ranges all over the planet. They published many complex, carefully constructed, laboriously measured theories and reconstructions to support this rock-cooling theory of mountain building.
However, the greatest strength in tackling a problem using the scientific method is that eventually the facts force the abandonment of incorrect theories. Those theories might result in great advances and shape decades of debate and investigation, but eventually the accumulation of better measurements and explanations will cause a shift in thinking. In this way, the great scientific theories focus, shape, and direct generations of those researchers striving to understand the universe.
An Earth-Shaking Theory: Plate Tectonics
In the case of the mystery of the formations of mountains, the theory of plate tectonics provided the vital framework to understand both the rise of mountains and the evolution of the surface of the planet. This once-radical and ridiculed theory, now widely accepted by geologists, suggests that the surface of the earth is divided into seven major slabs, or plates, of thin, brittle crust along with eight minor plates that fit together over the entire planet's surface like puzzle pieces. These light, hard slabs of rock—some outlining ocean basins or carrying entire continents—float on top of the hotter, deeper rock of the mantle , which comprises about 84 percent of our planet's volume and extends from a depth of about 4 to 22 miles (7 to 35 km) below the surface some 1,800 miles (2,900 km) down to the earth's superhot core. Heat from the earth's core travels outward and makes temperatures in the partially melted upper mantle as high as 932°F to 1,652°F (500°C to 900°C). That heat is the engine that makes earth's tectonic plates grow, melt, move, and interact with each other over time, creating volcanoes, causing earthquakes, building mountains, and slowly changing earth's surface over millions of years. 
New rock is created at the edges of tectonic plates. These plates are created along fissures in the seafloor, where magma rises up to create great chains of undersea mountains like the Mid-Atlantic Ridge. This upwelling magma forces the plates on either side to move away from the ridge. Since the surface area of the earth remains fixed, these moving crustal plates must go somewhere. So opposite every system of undersea ridges where new crust is manufactured lies a zone in which the same growing plate is destroyed. Such colliding plate edges either plunge down beneath the next plate in line or pile up in titanic head-on collisions with other plates.
Ten Mountains
These two alternatives account for most of the mountain ranges on the planet and for the division of this book. First, we will look at the mountain ranges caused by the head-on collision between two crustal plates. Such pile-ups of rock have raised the tallest and most massive mountain ranges on earth, including the Himalayas. The latter part of this book examines volcanic mountains formed when volcanic hot spots cause an isolated mountain range in the middle of a crustal plate (such as Hawaii's Mauna Kea) or when a buried crustal plate melts and fuels a volcanic chain of mountains as the pressurized, melted magma escapes to the surface. (This is partly how the Andes mountains were formed.) 
Oceanic Crust
The surface of the earth itself is essentially divided into two basic types of rock. First, most of the planet is covered by a dense, heavy layer of oceanic crust, mostly basalt and other volcanic rocks and magma. This dense igneous rock wells up along a great network of fissures running for thousands of miles, dividing the surface of the planet into seven major crustal plates. The upwelling of basalt that forms oceanic crust is driven by great convection currents at deeper levels. These great masses of heated, roiling, malleable rock form the bulk of the earth's mass, kept hot and fluid by the decay of radioactive elements in the deeply buried rocks. The light, brittle crust of the earth is a thin outer layer on this molten and semimolten mass of the hidden core and mantle layers, like the skin on a grape. Geologists believe this continual boiling in the earth's core is transmitted outward through the rocks of the mantle and boil up against the underside of the crust.
Along the cracks in the crust that form the edges of the crustal plates, this molten rock pressing upward from below moves toward the surface, producing most of the planet's volcano es and earthquakes. As a result, new crust is continually created along these massive fissures in the seafloor, forcing aside the older rock. This creates a virtual geologic conveyor belt of rock as new magma forces apart plates along spreading centers. At the other end of the conveyor belt wait undersea trenches—the geological dark twins to the spreading centers of the undersea ridges. The trenches form where two oceanic plates press against one another and one gets forced down beneath the other. So the seafloor is mostly composed of this relatively young igneous rock, created at the spreading centers and driven back below the surface 50 million to 300 million years later deep beneath the trenches. So ocean crust is young, dense, volcanic rock.
Continental Crust
The second type of rock at the surface of the earth is geologically quite different and mostly forms the rock of the continents. Generally, the continental rocks are much lighter, varied, and older than the oceanic crust. In effect, the lighter rocks that comprise the continents are "floating" on top of the dense oceanic crust. Some portions of the continents are chunks of oceanic crust uplifted and stranded, but most of the continental rocks are lighter igneous and metamorphic rocks loaded with quartz and silica, or layered sedimentary rocks like sandstone, composed of layers deposited on shallow sea bottoms or valleys, then buried and fused. Once these rocks erupt onto the surface of the continents or get pasted onto the edge of an existing continent, they may remain at the surface for billions of years. That is why the oldest rocks on the seafloor are only a few hundred million years old, while the oldest continental rocks are nearly two billion years old.
The mountains of the earth, therefore, are really the outward evidence of titanic forces. And that is why the study of these mountain chains has revealed deep truths about the evolution of the planet.
Mount Everest

Renowned mountain climbers Scott Fischer and Rob Hall planned their climbs to the top of the world's tallest mountain above sea level with exacting care. They had climbed so many of the world's most dangerous peaks, including Everest, that even relatively inexperienced climbers felt emboldened by having them along as guides to climb the 29,030-foot (8,850-m) mountain, a frozen jumble of rock forced five miles (8 km) upward by the devastating, slow-motion collision of continents. None of them knew that they stood on the brink of the most infamous tragedy in mountain climbing history, the perfect storm of miscalculation and bad luck, which horrified the world and underscored the strange and abiding human fascination with the struggle to reach the top of the mountain.
Few would have expected peerless climbers like Fischer and Hall to wind up at the epicenter of tragedy. Each led a separate expedition on that fatal day. An unprecedented eight climbe