This slide introduces the basic concept of tectonic movement. It is mainly focused on, causes of plate movement, rate of movement, consequences of movement, and some natural phenomena related to tectonic movement.
2. Introduction
The surface of the Earth is split up into several large
sections of rock called tectonic plates. A tectonic
plate includes the Earth's crust and upper mantle.
Earth has a rigid outer layer, known as
the lithosphere, which is typically about 100 km (60
miles) thick and overlies a plastic (moldable, partially
molten) layer called the asthenosphere. The
lithosphere is broken up into seven very large
continental- and ocean-sized plates, six or seven
medium-sized regional plates, and several small
ones. These plates move relative to each other,
typically at rates of 5 to 10 cm (2 to 4 inches) per
year, and interact along their boundaries, where
they converge, diverge, or slip past one another. 2
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Gobinda Kirtonia, Lecturer, CE, DIU 3
4. The Tectonic Plates move relative to each other, typically at rates of 5
to 10 cm (2 to 4 inches) per year, and interact along their boundaries,
where they converge, diverge, or slip past one another. Such
interactions are thought to be responsible for most of Earth’s seismic
and volcanic activity, although earthquakes and volcanoes can occur
in plate interiors. Plate motions cause mountains to rise where plates
push together, or converge, and continents to fracture and oceans to
form where plates pull apart, or diverge. The continents are
embedded in the plates and drift passively with them, which over
millions of years results in significant changes in Earth’s geography.
Gobinda Kirtonia, Lecturer, CE, DIU 4
5. Types of Plate Movements
Divergent (Spreading):This is where two plates move away from each
other. Molten rock from the mantle erupts along the opening, forming new
crust. The earthquakes that occur along these zones, called spreading
centers, are relatively small. The Great Rift Valley in Africa, the Red Sea
and the Gulf of Aden all formed as a result of divergent plate motion.
Convergent (Colliding): This occurs when plates move towards each
other and collide. When a continental plate meets an oceanic plate, the
thinner, denser, and more flexible oceanic plate sinks beneath the thicker,
more rigid continental plate. This is called subduction.
Transform: When two tectonic plates slide past each other, the place
where they meet is a transform or lateral fault. The San Andreas Fault is
one of the best examples of lateral plate motion.
Gobinda Kirtonia, Lecturer, CE, DIU 5
6. Continental drift
The continental drift hypothesis was developed in the early part of the 20th
century, mostly by Alfred Wegener. Wegener said that continents move around
on Earth’s surface and that they were once joined together as a single
supercontinent. Alfred Wegener proposed that the continents were once united
into a single supercontinent named Pangaea, meaning all earth in ancient
Greek. He suggested that Pangaea broke up long ago and that the continents
then moved to their current positions. He called his hypothesis continental
drift. If the current continents are placed together, they fit together like a
puzzle, which is evident to validate Wegner’s Theory. Other evidences like
rock of same type, fossils, same mountain formations are found at the edge of
current continents.
Gobinda Kirtonia, Lecturer, CE, DIU 6
8. Sea-floor Spreading
The seafloor spreading hypothesis was proposed by the American
geophysicist Harry H. Hess in 1960. Hess postulated that molten material
from Earth’s mantle continuously wells up along the crests of the mid-ocean
ridges that wind for nearly 80,000 km (50,000 miles) through all the
world’s oceans. As the magma cools, it is pushed away from the flanks of
the ridges. This spreading creates a successively younger ocean floor, and
the flow of material is thought to bring about the migration, or drifting
apart, of the continents. The continents bordering the Atlantic Ocean, for
example, are believed to be moving away from the Mid-Atlantic Ridge at a
rate of 1–2 cm (0.4–0.8 inch) per year, thus increasing the breadth of
the ocean basin by twice that amount.
Gobinda Kirtonia, Lecturer, CE, DIU 8
