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Table of contents
Introduction
Earth’s surface relief features encompass the vertical variations in elevation across landscapes, playing a significant role in shaping the planet’s topography. These relief features, such as the low plains of Nebraska and Saskatchewan, the rolling foothills along mountain ranges, and the towering peaks of the Rockies and Himalayas, define the undulating form of Earth’s surface.
This article explores the profound impact of relief and topography on human history, delves into the orders of relief, and highlights the advancements in technology that have revolutionized our understanding of Earth’s relief and topography.
The Significance of Relief and Topography
Relief and topography have played a crucial role in shaping human history. High mountain passes have both protected and isolated societies, while ridges and valleys have dictated transportation routes. The vast plains have necessitated the development of faster methods of communication and travel. Earth’s topography has not only stimulated human invention but also spurred adaptation to the diverse landscapes that cover the planet.
Crustal Orders of Relief
Advancements in technology, such as the global positioning system (GPS) and computer capabilities, have greatly enhanced our understanding of Earth’s relief and topography. Scientists can now transform elevation data into digital elevation models (DEMs) that aid in the scientific analysis of topography, slope characteristics, and local stream-drainage patterns. The U.S. Geological Survey has created a digitized shaded-relief map of the United States, incorporating 12 million spot elevations with high precision. The “A Tapestry of Time and Terrain” website, developed by the USGS, offers a virtual map that combines this data with colored geologic regions and detailed topography.
Orders of Relief
To facilitate description and analysis, geographers classify the landscape’s topography into three orders of relief. These orders categorize landforms based on their scale, ranging from vast ocean basins and continents to local hills and valleys.
1. First Order of Relief
This order encompasses the largest landforms, including continental platforms and ocean basins. Continental platforms refer to the crustal masses residing above or near sea level, including undersea continental shelves. Ocean basins, which lie entirely below sea level, constitute a significant portion of Earth’s surface.
2. Second Order of Relief
The second order of relief includes intermediate-scale landforms found in both continents and ocean basins. Examples of continental features in this order include mountain masses, plains, lowlands, and the great rock cores known as “shields” that form the heart of each continent. In ocean basins, second-order relief features comprise continental rises, slopes, abyssal plains, mid-ocean ridges, submarine canyons, and subduction trenches.
3. Third Order of Relief
The third order of relief encompasses smaller-scale landforms, such as individual mountains, cliffs, valleys, and hills. These features are identifiable as local landscapes, contributing to the intricate tapestry of Earth’s topography.
Understanding Hypsometry
Hypsometry, derived from the Greek word “hypsos” meaning “height,” provides a hypsographic curve illustrating the distribution of Earth’s surface area and elevation relative to sea level. Despite Earth’s overall diameter of approximately 12,756 km (7926 mi), the surface exhibits relatively low relief, with a mere 20 km (12.5 mi) separating the highest peak from the lowest oceanic trench.
For perspective, Mount Everest stands at an elevation of 8.8 km (5.5 mi) above sea level, while the Mariana Trench reaches a depth of 11 km (6.8 mi) below sea level. Notably, the measurement for the summit of Mount Everest was revised to 8,850 m (29,035 ft) in November 1999, as announced in a significant geographic milestone.
The average elevation of Earth’s solid surface is primarily underwater, with a depth of -2,070 m (-6,790 ft) below mean sea level. Exposed land, on the other hand, has an average elevation of only +875 m (+2,870 ft), while the average depth of the ocean reaches -3,800 m (-12,470 ft).
These figures highlight that, on average, the oceans are much deeper than the continental regions are high, emphasizing the prominence of underwater ocean basins and their role in shaping Earth’s largest “landscape.”
Earth’s Topographic Regions
Further categorizing the three orders of relief, geographers have generalized them into six distinct topographic regions: plains, high tablelands, hills and low tablelands, mountains, widely spaced mountains, and depressions. Each region is defined by an arbitrary elevation or descriptive limit, which is commonly used to classify the type of topography present.
1. Plains
Extensive plains dominate four of Earth’s continents, characterized by low local relief of less than 100 m (325 ft) and gentle slope angles of 5° or less. Some plains reach high elevations exceeding 600 m (2,000 ft), with the high plains in the United States surpassing 1,220 m (4,000 ft).
2. High Tablelands
Notable high tablelands include the Colorado Plateau, Greenland, and Antarctica, with elevations exceeding 1,520 m (5,000 ft). These regions showcase vast elevated plateaus that contribute to Earth’s diverse topography.
3. Hills and Low Tablelands
Africa is predominantly dominated by hills and low tablelands, characterized by moderate relief and an intermediate scale of landforms.
4. Mountains
Mountain ranges are present on each continent and are distinguished by local relief exceeding 600 m (2,000 ft). These majestic landforms shape the rugged landscapes we often associate with dramatic scenery and geological diversity.
5. Widely Spaced Mountains
This category encompasses mountains that are isolated or separated by significant distances. These widely spaced mountains contribute to Earth’s varied topography and add uniqueness to specific regions.
6. Depressions
Depressions represent areas with lower elevation relative to the surrounding topography. They can include valleys, basins, and other landforms that are characterized by their concave shape and lower relief.
Earth’s topography is characterized as plains, high and low tablelands, hills, mountains, and depressions. [After R. E. Murphy, “Landforms of the World,” Annals of the Association of American Geographers 58, no. 1 (March 1968). Adapted by permission.].
Dynamic Nature of Relief and Topography
It is crucial to note that Earth’s relief and topography are continually evolving due to the ongoing processes that shape the Earth’s crust. Tectonic forces, erosion, deposition, and other geological processes contribute to the constant change and reshaping of our planet’s surface. Understanding these dynamic processes is essential for studying Earth’s relief features and the intricate interplay between landforms and geological phenomena.
Conclusion
Earth’s surface relief features, encompassing various orders of relief and topographic regions, provide a remarkable window into the dynamic nature of our planet. From the vast continental platforms and ocean basins to the intricate details of local landscapes, Earth’s relief and topography have shaped human history, stimulated innovation, and continue to intrigue scientists. As technology advances, our understanding of these features deepens, offering new insights into the complex tapestry of Earth’s topography and the forces that shape our world.
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