A detailed description of Glacial control theory regarding the origin of coral reefs

1. Dr. Meenakshi Prasad
Assistant Professor
P.G. Deptt. Of Geography
Magadh University, Bodh Gaya
Theories of Origin of Coral Reef
Source : google images

2. Disclaimer
The material for the presentation has been
compiled from various books and online sources
& it is for general information & educational
purpose only. While the author makes an
endeavor to keep the information up to date and
correct she makes no representation of any kind
about the completeness and accuracy of the
material. The information shared through this
presentation should be used for educational
purposes only.

3. Content
• Introduction
• Glacial Control Theory
• Characteristics of the
theory
• Criticisms
Source: google images

4. Introduction
• There is no dispute about the origin of fringing coral reefs, but
the base of barrier reefs and atolls is sometimes at such a
depth where it is not possible for the coral polyps to survive.
To solve this problem, some theories have been given about
the origin of coral reefs, out of which three theories have
special recognition. These are –
• Land Subsidence Theory by Darwin
• Stand Still Theory by Murray &
• Glacial Control Theory by Daly

5. • The most widely recognised & accepted amongst the three
theories is the Land Subsidence Theory. It is followed by the
Glacial Control Theory & Stand Still Theory respectively.
Source : google images

6. • The Glacial Control Theory was propounded by Daly in 1915
on the basis of the study of the coral reefs of the Hawaiian
islands.
• This is also a type of stand still theory in which the change in
the sea level and has been considered as the basis for the
development of coral reefs.
• According to this theory, three types of coral reefs are related
to three different topography , i.e. the fringing reef is
associated with the coast, the barrier reef with the sub-
marine platforms and plateaus & the atolls are associated
with islands.
Glacial Control Theory of Daly

7. • The change in sea level is related to the change in
temperature.
• Therefore, Daly considered temperature change the basis for
the development and destruction of coral polyps and
attempted to explain the origin of coral reefs in the context of
glaciation.
• According to Daly, the Pleistocene glaciation / ice age has had
an impact on the development of coral reefs.
• At the time of the Pleistocene glaciation, the sea level had
gone down by 100–150 m and many pre-existing coral reefs
came above the sea level.

8. • On coming above the sea level, their tops became almost flat
due to erosion and acquired a platform shape.
• The lowering of the sea level also led to the formation of
platforms and steps created by the work of ocean waves along
the continental shelves and the islands.
• After the Pleistocene glaciation, when the sea level began to
rise, coral polyps started developing on these different types
of platforms.
• Fringing reefs were formed on the narrow wave-cut platforms
alond the new continental shelves.

9. Origin of Coral Reefs according to Daly
Sourec: google images

10. • When the coral polyps developed on the broad wave-eroded
platforms situated away from the coast, it led to the
formation or barrier reefs with deeper and broader lagoons.
• Thick horse-shoe shaped reefs or atolls having steep slopes
developed on the platforms situated along the islands.
• According to Daly, lagoons of uniform depth were formed
between the reefs and the land because of uniform lowering
of sea level due to glaciation during Pleistocene ice age.

11. Source: google images

12. Characteristics
(i) The most important characteristic of this theory is that climate
change has been linked to the development of coral reefs,
which is a reality.
(ii) If this theory is considered the basis, then the coral reefs of
high latitudinal regions are explained.
(iii) The thickness of the coral reef is confirmed by this theory.
(iv) This theory gives a scientific explanation of the depth of the
lagoon and the coral reefs.

13. Criticism
• According to this theory, the depth of all the lagoons of atolls
& barrier reefs should be uniform, but actual observations do
not validate this concept. According to W.M. Davis the depth
of different lagoons varies considerably. Not only this, the
depth even varies within a lagoon.
• The coasts might have been cliffed due to wave erosion during
the phase of the lowering of sea level during Pleistocene Ice
Age. Thus, the cliffs formed during the glacial period should
also be present now but they are seldom found.
• Debris or mud are found on the surface of the platform which
is not favourable for the growth of coral polyps.

14. • Although this theory explains the thickness of the coral reef,
but the thickest coral reef of Bikini Island is not explained by
it.
• Hence this theory also has its limitations due to the facts
mentioned above.

15. Conclusion
• Of all the theories of the origin of coral reefs, Darwin's
Subsidence theory is the most recognized because it is a
theory that explains the thickness, the depth of the lagoon
and the slopes of most coral reefs of the world.

16. References
• Sharma, R.C. & Vatal, M. : Oceanography for Geographers,
Chaitanya Publishing House, Allahabad, 1995
• Singh. S : Physical Geography, Prayag Pustak Bhawan,
Allahabad,2012

17. Source: google images