Landforms: Mountains, Valleys, Plains, and Canyons - Second Grade Science
If you take a journey across the continents, you will notice that Earth's surface is not completely flat. Instead, it is sculpted into a spectacular variety of natural shapes and features called landforms. From snow-capped mountain peaks piercing the clouds to wide, grassy plains rolling toward the horizon and deep, colorful canyons carved into solid stone, landforms tell the story of Earth's dynamic geologic history.
What is a Landform?
A landform is a natural physical feature on the surface of the Earth. Landforms are created over thousands or millions of years by powerful natural forces such as tectonic plate movements, volcanic eruptions, rushing water, and blowing winds.
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| MAJOR EARTH LANDFORMS |
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| 1. MOUNTAINS ----> High, rugged land rising to sharp peaks |
| 2. VALLEYS ----> Low areas between mountains or hills |
| 3. PLAINS ----> Flat, sweeping stretches of open land |
| 4. CANYONS ----> Deep, narrow chasms with steep cliff walls |
| 5. PLATEAUS ----> Flat-topped elevated highland tables |
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Mountains: Giants of the Earth
A mountain is a landform that rises steeply at least 1,000 feet (300 meters) above the surrounding terrain, culminating in a summit or peak.
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| ANATOMY OF A MOUNTAIN |
| |
| /\ <-- PEAK / SUMMIT (Snow-covered) |
| / \ |
| / /\ \ <-- STEEP ROCKY SLOPES |
| / / \ \ |
| ===============/ / \ \================ BASE |
| Formed when tectonic plates collide or volcanoes erupt! |
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How Mountains Form
Fold Mountains: When two gigantic continental plates crash together over millions of years, the crust crumbles, buckles, and folds upward into the sky. The Himalayas (home to Mount Everest) and the Rocky Mountains formed this way. Volcanic Mountains: When molten magma erupts through Earth's crust, cooling lava and ash build up layer upon layer, creating towering cone-shaped mountains like Mount Rainier and Mount Fuji.
Valleys: The Lowlands Between Heights
A valley is a low area of land situated between mountain ridges or hills. Valleys usually feature fertile soil and often have a river or stream running along their floor.
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| V-SHAPED VS. U-SHAPED VALLEYS |
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| V-SHAPED VALLEY (Carved by RIVERS) U-SHAPED VALLEY (GLACIERS) |
| \ / | | |
| \ / | | |
| \ / \__________/ |
| \/ (River cutting) (Ice bulldozer) |
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V-Shaped Valleys (Carved by Water)
Swift mountain streams cut sharp V-shaped grooves into rock as rushing water and tumbling boulders scour the riverbed deeper and deeper into the rock.
U-Shaped Valleys (Carved by Ice)
When a massive glacier creeps down a mountain pass, it acts like a giant frozen bulldozer. It gouges rock from both the floor and sides, leaving behind a wide, flat-bottomed valley with steep, vertical walls shaped like the letter U.
Plains and Plateaus: Flat Terrains
Not all landscapes are steep and rocky. Many expansive regions of Earth are smooth, flat, or gently rolling.
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| PLAINS VS. PLATEAUS |
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| COASTAL / INLAND PLAINS ELEVATED PLATEAU (Tableland) |
| ___________________ |
| / \ |
| ______________________________ / \ |
| Low elevation, flat grassland High elevation, flat top |
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Plains
Plains are vast stretches of nearly flat land with low elevation. Because rivers deposit rich silt during annual floods, plains often have fertile soils, making them the agricultural breadbaskets of the world (such as the Great Plains of North America).
Plateaus: Tables in the Sky
A plateau is an elevated landform that rises sharply above surrounding terrain on at least one side, but features a flat, table-like top. The Colorado Plateau covers four southwestern states and sits thousands of feet above sea level.
Canyons: Earth's Deep Chasms
A canyon is a deep, narrow gorge with steep, sheer cliff walls, usually carved over millions of years by the relentless flow of a river.
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| THE GRAND CANYON |
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| Rims: Level Plateau Surface Rims: Level Plateau Surface |
| |=====| |=====| |
| | \ / | |
| | \ Exposed layers of sedimentary rock / | |
| | \ / | |
| | `======================|========================' | |
| ~~~~~~ |
| Colorado River at the bottom! |
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The Grand Canyon
The Grand Canyon in Arizona is one of the natural wonders of the world. Over six million years, the Colorado River sliced through rock layers over a mile deep! Looking down into the canyon reveals colored rock strata that display Earth's history like the pages of a giant stone book.
Chapter Review Exercises
Question 1: What is a landform, and what are two natural forces responsible for shaping landforms over time?
Question 2: How can a geologist tell whether a mountain valley was carved by a flowing river or by a crawling glacier?
Question 3: What is the main structural difference between an open plain and an elevated plateau?
Question 4: Describe how the Colorado River carved the Grand Canyon out of solid rock.
Solutions and Explanations
Solution 1: A landform is a natural physical shape or feature on Earth's surface. Landforms are created by forces such as the collision of tectonic plates, volcanic eruptions, flowing rivers, and weathering from wind and ice.
Solution 2: A valley carved by a river forms a sharp, narrow V-shape because the rushing water cuts downward along the riverbed. A valley carved by a glacier forms a broad, flat-bottomed U-shape with steep cliff sides because the massive ice sheet scraped and widened the entire valley floor like a bulldozer.
Solution 3: An open plain is a broad, low-elevation expanse of nearly flat land. A plateau is an elevated highland that rises steeply high above surrounding land, but features a flat, level top like a giant table.
Solution 4: Over millions of years, the Colorado River rushed across the elevated Colorado Plateau, carrying sand, gravel, and boulders in its current. These sediments acted like natural sandpaper, cutting through rock strata a mile deep into the Earth to create steep canyon walls.