Gujarat is a
land with multiple landforms. It has the mainland Gujarat with flat
alluvial plain with a river system that originates in the higher eastern
reaches of the state. Then the Saurashtra part of the state is dominated
by basalt domes and ridges and Kachh region has the great Rann, the salt
pans. Since times immemorial these landforms have been experiencing the
nature's ire. The science of geology is such that it gives a third eye
to the person well versed with the subject and he can probe the
landforms and get answers to several how and whys. Through the following
lines I am going to unravel some of the past mysteries of Gujarat as
seen by L.S. Chamyal, D.M Maurya and Rachna Raj of Department of
geology, M.S. University of Baroda, Vadodara, India. They worked
extensively in the state and collected evidences about the past
environmental ups and downs of Gujarat as depicted by the landforms and
river systems of the state.
Gujarat is an area with a checkered tectonic history. It is an area
where in the past the sea has often engulfed the coasts and has
retreated again. These actions of nature are preserved in the river
systems. Rivers are extremely sensitive to tectonic and sea level
changes. Fluvial systems (river systems) of semi arid and arid areas of
Gujarat show a strong structural control on he drainage architecture and
the landscape of the area, which has evolved due to neotectonism and
paleoenvironmental changes, say Chamyal and his colleagues in their
paper published in the journal, Quaternary International.
The part of the earth between the Tropic of Cancer on the north of
Equator and Tropic of Capricorn, south of Equator is known as the
Tropics. The seasons in the Tropics are dominated by the movement of
Tropical Rain belt, which oscillates between the northern and the
southern tropics over the year, thus causing the dry and the wet seasons
in turn, says the Wikipedia. The Tropic of Cancer passes through the
state of Gujarat. With Thar Desert bordering the northern part of the
state and the Arabian Sea one west, the climate of Gujarat is much
influenced by these factors. There is so much variation in the climate
in the state due to uneven distribution of rainfall that it is presently
categorized in to sub-humid, semi-arid and extremely arid zones.
The climate affects the landforms. In addition the landforms are also
affected by the tectonic disturbances. Indian plate as it began
colliding with the Tibetan Plate some 65 million years ago (m a), the
western continental margin of the plate began to fragment. Consequently
three rift valleys were formed at Kachh, Cambay and Narmada. These
valleys were connected with the sea till about 1.75 m a as confirmed by
the presence of marine sediments in these basins at depths. Once the
basins were filled up there were adjustments and rivers began to flow
through newly formed plains. Thus the sediments at higher levels are of
younger age and have been deposited by the rivers.
The Saurashtra peninsula made of basalts, on the other hand was a
tectonic as well as geomorphic high. If Rajkot is taken as centre the
streams from there flow out in all directions in Saurashtra. Saurashtra
was a high land as the Kachh and Cambay rift valleys were formed. And it
remains a highland even today. Thus, on the fringes of Saurashtra even
today sediments older than 1.75 m a are found. There are not many
studies available on how much was the ground movement and relative sea
level change in the past 1.75 million years. It seems during an
interglacial period some 125 thousand years ago (ka), the sea level was
much higher. As a result it extended inwards in mainland Gujarat as far
as Mahudi in the Sabarmati valley, Bhadarwa in the Mahi valley and Kotia
in the Narmada valley. This was confirmed by the Infrared stimulated
Luminescence studies of the clay rocks found along the onshore areas of
the above rivers. It was found that the sea level was seven metres
higher than the present day and the retreating sea left behind a thick
succession of sediments which are now present as vertical cliffs along
various river valleys. These sediments have layers of gravel in between.
It seems they were deposited in semi-arid to sub-humid climatic cycles
and in between in some rivers like Mahi there were floods which brought
the heavier sediments like gravels. Further studies of these sediments
showed that they were equivalent in age to Marine Isotopic stages 5 and
3, which is approximately 125 ka to 110 ka.
The wind-born sediments main land Gujarat were dated and it suggests
that arid phase set in as early as 22 ka before present (BP). However, a
further refinement in dates shows that sand movement was at peak some 14
ka BP. This was the period post Last Glacial Maxima, i.e. 18 ka years
BP. At the same time the sea had receded by about 120 m in the Gulf of
Cambay and Rann of Kachh. In other words these areas were part of the
main land at that time. Gujarat mainland remained arid till about 10 ka.
It appears that between 10 ka BP to 2 ka BP there was a humid phase in
the mainland of Gujarat. This is indicated by the sediments on the
Narmada flood plain. They are of the type of sediments found in the
sheet floods. Around 6 ka the sea reached its maximum and encroached
upon the mainland through the estuaries and submerged vast areas of
Ranns of Kachh, Okha and Nal region says Chamyal. Radiometric dates of
sediments from Mahi estuary reveal that the sea remained at the same
level till as late as 2 ka BP.
Since times immemorial rivers have fascinated man. Most of the best
habitats are along the rivers. The craving for converting the flood
pathways for human use continues. Gujarat is no exception. The rivers on
the other hand have their own ways. They often confuse even the nature.
For example regional slope of the area drained by Sabarmati, Mahi, and
Vishwamitri and Orsang rivers is southwest. These rivers on the other
hand have apparently captured E—W to ENE—WSW courses of their
tributaries. Thus Sabarmati has captured the course of Vatrak, the Mahi
has captured the course of Min, Mesri and Goma rivers, the Vishwamitri
has captured the course of E—W flowing smaller rivers and the Orsang has
captured the E—W flowing Heran and Unch rivers. Rivers often change
their courses and capture the channels of others. Often this happens
when the subsurface is in turmoil and the drainage is realigned. The
drainage system of Gujarat is influenced by the tectonic activity that
started in the later part of the last 1.75 million year history of the
earth of this region.
The geological, tectonic and climate history of Gujarat needs a thorough
detailed study to interpret the possible future changes in the courses
of the rivers and also in the behavior of the Rann. It is well known
that barely 2000 years BP the Rann of Kachh was not shallow; it was part
of the sea.
Gujarat is a progressive state. Despite upheavals in the past it has
emerged a winner and has progressed well. A detailed knowledge about the
land the coast will surely help the planner to develop the state in
harmony with nature.
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Gujarat is a
land with multiple landforms. It has the mainland Gujarat with flat
alluvial plain with a river system that originates in the higher eastern
reaches of the state. Then the Saurashtra part of the state is dominated
by basalt domes and ridges and Kachh region has the great Rann, the salt
pans. Since times immemorial these landforms have been experiencing the
nature's ire. The science of geology is such that it gives a third eye
to the person well versed with the subject and he can probe the
landforms and get answers to several how and whys. Through the following
lines I am going to unravel some of the past mysteries of Gujarat as
seen by L.S. Chamyal, D.M Maurya and Rachna Raj of Department of
geology, M.S. University of Baroda, Vadodara, India. They worked
extensively in the state and collected evidences about the past
environmental ups and downs of Gujarat as depicted by the landforms and
river systems of the state. 