Forces of Drifting: Pole-Fleeing Force, Tidal Force
Geography › Plate Tectonics and Distribution of Continents and Oceans · Topic 4.3
Wegener suggested two forces to drive the continents: the pole-fleeing force and the tidal force. The pole-fleeing force comes from the rotation of the Earth, whose equatorial bulge is acted on by centrifugal force, and was meant to push continents from the poles towards the equator. The tidal force, from the attraction of the Moon and Sun, was meant to drag the continents westward. Physicists showed that both forces are far too weak to move continents, and this was the main reason the theory was rejected for decades.
5 min read · UPSC Prelims · Geography · Plate Tectonics and Distribution of Continents and Oceans
At a Glance
- Pole-fleeing force Rotation pushes continents towards the equator
- Tidal force Moon and Sun drag continents westward
- Moving medium Sial floating through sima
- Main critic Harold Jeffreys
- Verdict Forces too weak
- Exam link UPSC Prelims, Geography: Plate Tectonics and Distribution of Continents and Oceans
Where Does It Fit?
This topic follows the evidence for drift and exposes its weakest part, the proposed driving forces. It shows why the theory had to be revised, which led to the convection idea and sea-floor spreading of the following topics. Previous topic: Evidence for Continental Drift: Jigsaw Fit, Matching Rock Ages, Tillite, Placer Deposits, Fossil Distribution. Next topic: Convectional Current Theory and Mapping of the Ocean Floor.
What Forces Did Wegener Propose?
Wegener suggested that the continents moved because of two forces. The first was the pole-fleeing force, a force that arises from the rotation of the Earth and its equatorial bulge and drives continents toward the equator. The second was the tidal force, the pull of the Moon and the Sun, which he suggested dragged the continents westward. The westward drift was used to explain why the Americas moved away from Europe and Africa and why the Himalayas and Alps formed through the northward movement of Gondwana and the closure of the Tethys.
What Are the Pole-Fleeing and Tidal Forces?
| Force | Meaning | Effect proposed by Wegener |
|---|---|---|
| Pole-fleeing force (Polflucht) | A force arising from the rotation of the Earth. Because the Earth bulges at the equator, the equatorial bulge is acted on by the centrifugal force of rotation, which is greatest at the equator | Pushes the continents away from the poles towards the equator, so that they drifted equatorward |
| Tidal force | The attraction of the Moon and the Sun, which raises tides in the ocean | Would drag the continents westward, because the Earth rotates towards the east and the pull lags behind. This was meant to explain the westward drift of the Americas |
Wegener thought that the continents, made of lighter sial, floated on the heavier layer of sima below, rather as icebergs float, and that the two forces together could push the continents slowly through it. In his view, the drift to the equator formed the Alpine-Himalayan mountains, which are near the equatorial belt of Pangaea, and the westward drift created the Rockies and the Andes at the leading edge.
Why Was the Theory Rejected at First?
Physicists showed that the forces proposed by Wegener were far too weak to move continents through the solid rock of the ocean floor. Tidal forces could not drag continents westward, and the pole-fleeing force was extremely small. Wegener could not explain how continents could plough through oceanic crust. Although the evidence of fit and fossils was convincing, the lack of a mechanism meant that most geologists did not accept the theory during his lifetime, and he died in 1930 on an expedition to Greenland. As an analytical point, this is a good example of how an idea backed by evidence can be set aside until a mechanism emerges, and in this case the mechanism arrived three decades later in the discovery of seafloor spreading.
Why Were These Forces Wrong?
- Too weak: the British geophysicist Harold Jeffreys and others calculated that the pole-fleeing force and the tidal drag are many times too small to move a continent. A tidal drag strong enough to move continents would stop the Earth’s rotation in a short time.
- No path through the ocean floor: geophysicists argued that the strong oceanic crust could not be ploughed through by thin continents. Later work showed that continents do not plough through the ocean floor at all but ride on plates.
- Wrong pattern: drift to the equator and the west does not fit the movements actually observed, which include India moving north and the Atlantic opening in both directions.
As an analytical point, Wegener was right about what happened, but wrong about why. The correct driving forces, which are slab pull, ridge push and mantle convection, were found only after the ocean floor was explored in the 1950s and 1960s, and are set out in Rates and Forces of Plate Movement. The first step towards that explanation was made in Convectional Current Theory and Mapping of the Ocean Floor.
Why Is This Topic Important?
- Foundation Precursor to plate tectonics
- Evidences Frequent Prelims theme
- India Gondwana link
What Came Next?
The next topic describes the convection current theory and the mapping of the ocean floor that led to a better explanation. Next topic: Convectional Current Theory and Mapping of the Ocean Floor.
Key People and Terms
- Pangaea Single supercontinent
- Panthalassa Ocean around Pangaea
- Laurasia Northern landmass
- Gondwanaland Southern landmass
- Tillite Rock formed from glacial deposits
- Glossopteris Fossil seed fern of Gondwana
Exam Corner
Points to Remember
- Proposed by Alfred Wegener in 1912.
- Pangaea began to split about 200 million years ago.
- Laurasia in the north, Gondwanaland in the south.
- Forces: pole-fleeing and tidal.
- Evidence included Glossopteris and tillite.
Do Not Confuse With
- Pangaea and Panthalassa Land versus ocean
- Laurasia and Gondwanaland North versus south
- Continental drift and plate tectonics Continents moving alone versus carried on plates
Memory Hook
One land, one sea; two pieces, many parts; fit, fossils, ice and rock, but no force to push.
Mains Angle
Questions ask for evidence and limitations. These points add depth.
- Evidence Fit, fossils, glaciation
- Limitation No adequate mechanism
- Legacy Led to seafloor spreading
A Question You May Face
An original practice question, not a past paper question.
“Critically examine Wegener’s theory of continental drift and the evidence for it.”
How to Answer
- Theory Pangaea and its breakup.
- Evidence Fit, fossils, rocks.
- Criticism Forces too weak.
- Legacy Plate tectonics.
GS Relevance
Frequently Asked Questions
What forces did Wegener suggest for drift?
Wegener suggested two forces: the pole-fleeing force, arising from the Earth's rotation and the equatorial bulge, and the tidal force, the pull of the Moon and the Sun. Scientists later found that both were far too weak to move the continents.
Why was the continental drift theory not accepted?
The theory was not accepted because Wegener could not give a force strong enough to move continents through the ocean floor. The lack of a convincing mechanism overshadowed the evidence, and acceptance came only after seafloor spreading and plate tectonics were developed.
What is the pole-fleeing force?
The pole-fleeing force is a force arising from the Earth's rotation. Wegener argued that the equatorial bulge is acted on by centrifugal force, which would push the continents from the poles towards the equator. Calculations later showed that this force is far too weak to move continents.
How was the tidal force supposed to move the continents?
Wegener proposed that the attraction of the Moon and the Sun, which raises tides, drags the continents westward, as the Earth rotates eastward beneath the pull. This was to explain why the Americas drifted west, but the tidal drag is too small to have such an effect.
Why was Wegener's theory rejected at first?
The theory was rejected mainly because Wegener could not give a believable force strong enough to move continents. Physicists such as Harold Jeffreys showed that the pole-fleeing and tidal forces were many times too weak, and nobody could explain how continents could plough through the ocean floor.
PYQ Practice — Statement Analysis
1 Wegener's forces were considered more than enough to move continents.
They were far too weak.
2 The pole-fleeing force acts to move continents towards the equator.
It arises from the Earth's rotation.
3 The tidal force was proposed to drive the continents towards the poles.
It was proposed to drag them westward.
4 Wegener's proposed forces were found to be too weak.
This led to his theory being rejected.
Past Mains Questions on This Topic
This topic comes under Plate Tectonics and Distribution of Continents and Oceans. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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