It is a term that is mostly used in Geology, Geophysics, and Geodesy or Geography and Earth Science, its first proposal was made in 1889, by C. Dutton who was an American Geologist. Our Earth has different layers and these layers have different properties and this term is one of the phenomena that deals with some of these layers. In this article, we will be talking about this, one of the important phenomena and will learn about what is Isostasy, meaning, Isostasy Geology definition and examples, etc.
Introduction
The Earth can be divided into various layers such as Crust, Mantle, Outer Core and Inner Core based on chemical composition and lithosphere, asthenosphere & mesosphere based on physical properties. The lithospheric crust of the Earth lies on the upper mantle ie. Asthenosphere. The upper mantle is considered dense thus, the crust floats on it rather than simply resting on it. Here, we will discuss one of the phenomena that describe the relationship between the two.
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Isostasy Meaning
This term is made up of two Greek words ie. isos which means equal and stasis which means standstill. The crust of the Earth is lighter than the layer it lies on, i.e. on the mantle which is denser and it floats on this mantle sheet. Isostasy is nothing but a phenomenon that keeps a balance between the lithospheric crust and the mantle of the Earth. It is also termed as isostatic equilibrium. It helps in keeping the balance between the forces that leads to upliftment or sinking of the lithospheric crust.
There are some standard definitions are written below which describes Isostasy:
Isostasy Geology Definition
Examples
We have read about the Isostasy which helps in maintaining the equilibrium of the portion whenever the weight is lifted and added there. Let's have a look at the examples:
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1. Here, in this diagram the right side is non - static equilibrium whereas the left shows the isostatic equilibrium. The relationship is similar to the left side, the upper mantle is denser thus the upper crust is floating on it. Whenever more weight is added there, then it starts sinking downwards in the mantle whereas it starts uplifting whenever the weight is lifted.
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2. Here, the diagram shows the time of the formation of the mountain. On the left side, during its formation when more weight is added, the crust sinks in the mantle and on the right side, when after several years, due to erosion and weathering, the weight is lifted, then the crust starts lifting.
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3. Let's see the same isostatic process in glaciation. In Greenland, the more weight of the ice sheets will lead to its sinkage towards the mantle. It will rebound whenever this melts but that will take several years to happen.
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4. This diagram shows the period when the ice melts completely and the crust starts lifting upwards. The melting of the ice sheets will take a huge number of years but the way climate change is happening, it can be faster
Conclusion
Thus, to sum up we can say that we have studied one of the major and important phenomena that deal with layers of the crust and the upper mantle and helps in balancing the crust which floats on the mantle. We have covered Isostasy, its meaning, Isostasy Geology definition and its examples with diagrams. This article will help you whenever you will study the layers of the Earth in Geology, Geography or other Earth Sciences etc.
We have learned about Isostasy comprehensively. Let's have a look at some of the related questions:
FAQs on Isostasy
1. What is the fundamental principle of isostasy in physical geography?
Isostasy is the principle that describes the state of gravitational equilibrium between the Earth's rigid outer layer, the lithosphere, and the more fluid-like upper mantle, the asthenosphere, upon which it floats. The concept suggests that different crustal blocks (like mountains, plains, and ocean floors) float at elevations that depend on their thickness and density, much like icebergs of different sizes float in water.
2. How does the Earth's crust achieve isostatic equilibrium?
The Earth's crust achieves isostatic equilibrium through a process called isostatic adjustment. When a significant weight is added to the crust, such as through the formation of a large mountain range or a massive ice sheet, the lithosphere sinks deeper into the asthenosphere. Conversely, when weight is removed, for instance through the erosion of mountains or the melting of glaciers, the lithosphere slowly rises or rebounds to restore the balance.
3. What is the difference between Airy's and Pratt's theories of isostasy?
Both theories explain how isostatic balance is maintained, but they propose different mechanisms:
Airy's Theory: This theory assumes that the crust has a uniform density everywhere. To maintain balance, thicker crustal blocks (like mountains) sink deeper into the asthenosphere, creating deep 'roots'. Thinner crustal blocks (like ocean floors) have shallower roots. It's often summarised as 'different thicknesses, same density'.
Pratt's Theory: This theory assumes the crust has varying density. It proposes that all crustal blocks extend to a uniform depth, known as the 'level of compensation'. Higher features like mountains are less dense, while lower features like ocean basins are denser. This is often summarised as 'different densities, same thickness' above the compensation level.
4. How does isostasy explain the formation and height of major landforms like mountains and plateaus?
Isostasy is crucial for explaining the elevation of landforms. For mountains, their immense mass causes the underlying lithosphere to form a deep root that displaces the denser asthenosphere, providing buoyant support. As mountains erode over millions of years, the removal of mass reduces the load, causing the crust to experience isostatic uplift. This process ensures that even very old mountain ranges can remain significantly elevated, as their roots continue to push them upward as the peaks wear down.
5. Can you provide a real-world example of isostatic adjustment happening today?
A classic and ongoing example of isostatic adjustment is the post-glacial rebound occurring in regions like Scandinavia, Scotland, and the Hudson Bay area in North America. During the last Ice Age, these areas were covered by massive ice sheets several kilometres thick. The immense weight of the ice depressed the crust. Since the ice melted around 10,000 years ago, these landmasses have been slowly rising, and they continue to do so today as the lithosphere returns to its equilibrium level.
6. Why is the concept of isostasy important for understanding geological processes?
The concept of isostasy is fundamental because it connects various geological phenomena. It is essential for understanding:
Plate Tectonics: It helps explain the different elevations of continental and oceanic crust.
Mountain Building (Orogeny): It explains how mountain ranges are supported and why they remain high despite erosion.
Sea-Level Changes: It helps differentiate between global (eustatic) sea-level rise and local (isostatic) land-level changes.
Geological Hazards: Understanding isostatic adjustments can be relevant for assessing the stability of coastal regions.
7. Who is credited with coining the term 'isostasy'?
The term 'isostasy' was coined in 1882 by the American geologist Clarence Dutton. He used it to describe the state of gravitational balance that exists across the Earth's surface, where lighter crustal material essentially 'floats' on the denser mantle material below.
