Relief and Structure of Goa - GOA PCS Exam Notes

Relief and Structure of Goa

Goa is almost entirely covered by rocks of the Goa Group belonging to the Dharwar Super Group of the ArchaeanlProterozoic age, except for a narrow strip at the north-eastern corner occupied by Deccan Trap of the Upper Cretaceous-Lower Eocene age.
The Goa Group consisting of green ‘schist species of metamorphic rock is divided into Barcem formation, Sanvordem formation, Bicholim formation and Vageri formation in the ascending order of superposition.
The narrow strip of Deccan Trap has some sporadic cover of laterite.
Iron and manganese are the chief minerals of economic importance.
Goa is a part of Konkan area.
Goa has hills, low and highland areas. Geographically Goa has mainly three natural divisions namely the Low lands, the Plateaus and the Mountain region.

Physical Features of Relief and Structure of Goa

Goa is very much similar geographically to the neighboring states of Maharashtra and Karnataka.
Physical geography divides the state into three geographical divisions.
These are Mountainous Region formed by Sahyadri Ranges in the east, Plateau Region in the center and low-lying river basins and coastal plains.
Having an average elevation of 800 m, Sahyadris Ranges are spread over an area of about 600 sq km. Some of the major peaks of the ranges include Sonsagar, Vaguerim, Morlemchogor and Catlanchimauli.
Almost all the rivers of Goa originate from this region. Central region of Goa has The plateaus ranging between altitudes of 30 m to 100 m are spread in the Central Region of the state.
The rivers of Mandovi and Zuari drain the major portions of the plains. The rivers with shallower basins include Chapora in the north and the Sal and the Kushavati in the south.
Having alluvial flats near the coastal regions, these basins form rich agricultural tracts. Some other major rivers that drain the state include Baga, Tiracol, Talpona, Mandovi, Zuari and Galgibagh.

Low Lands of Relief and Structure of Goa:

Low land area is mainly coastal lines.
It is about 110 km long.
Many beaches are along the coast in this area.
Many rivers flow east to east in this area therefore this area land is fertile.
This area is thickly populated.

Plateau Lands of Relief and Structure of Goa:

The plateau region is found between the mountain region in the east and the lowlands in the west.
Plateau land height ranges from 30 metres to 100 metres.
In this region mainly plenty of laterite stone is found.
It is used for building the houses.
Some of the part of plateau land is called headland of Goa. Light houses are built on these healdlands.
Land in the plateau region is not fertile; few crops are taken in this region.

Mountain region of Relief and Structure of Goa:

Sahyadri Mountains are to the east of South Goa.
This part is covered with dense forest. In this area, some of the mountains are very steep.
In the South Goa peaks are Chandranath at Paroda, Dudhsagan in Sanguemtaluka and Cormolghant in Canaconataluka.
Many streams and rivers flows from this region to lowands. In South Goa rivers are Zuari, Talpona, Sal and Galgibag.
Rivers are used for transporation.
Inland waterways play an important role in transport of minreal ores from the mining sites in Sanguemtaluka such as Costi, Kirpal, Netravalim, Rivona, Ducorcond and Kuddegal to the Mormugaoharbour for export South Goa is rich in natural resources like trees, iron and manganese ore.
It is exported mainly to Japan, South Korea and some European countries.

General Geological Setup of Relief and Structure of Goa

The regional geology in general and local geology in particular is very important in understanding hydrogeological characters of an area.
The occurrence and movement of groundwater directly depends on the openings within the rock formations.
The nature of rock type, the degree of rock deformation and the extent of weathering play a significant role in the formation of porosity.
The State of Goa is located on the Western Dharwar craton.
It constitutes the north-westerly extension of the greenstone-granitoid terrain of Karnataka, comprising rocks of the Peninsular Gneissic Complex (PGC) and Dharwar Supergroup of Precambrian age.
The PGC is well exposed along the Western Ghats in North Goa and around Chauri and Quepem in the South Goa.
The rocks of the Dharwar Supergroup are represented by the northern extension of the Shimoga schist belt locally classified as ‘Goa Group’.
The rocks of the PGC and the Goa Group are intruded by mafic-ultramafic complexes, younger granites and mafic intrusives.
A narrow strip in the north eastern corner of the State is covered by Deccan Traps of late Cretaceous-lower Eocene age.
Most of these rocks are often hidden below a thick weathered lateritic cap and/or a soil cover of varying thickness.
The oldest known rock found in Goa is the Anmod Ghat Trondhjemitic Gneiss.
The Peninsular gneisses are grey, medium to coarse grained, banded or migmatitic and grade in composition from Tonalite- Trondhjemite- Granodiorite.
These gneisses form the basement for the Goa Group of rocks.
The Goa Group of rocks consists of meta-volcanic and metasedimentary rock assemblage characterized by greywackes, argillites, tuffs, agglomerates, mafic lavas and banded iron formation.
It has undergone greenschist facies of regional metamorphism and is broadly comparable to the Chitradurga Group of Karnataka.
The Goa Group is divided into four formations, namely the Barcem, Sanvordem, Bicholim-Rivona and Vageri Formations in the ascending order of superposition.
The PGC and the Goa group of rocks have been intruded by Bondla mafic-ultramafic complex and granites which occur as plutons, plugs and apophyses, the most important being the porphyritic Canacona Granite and the Dudhsagar Granite.
These are followed by mafic intrusives.
These rocks are overlain by Deccan Traps represented by horizontally disposed massive and vesicular basaltic lava flows.
During the late Cenozoic period the rocks were subjected to intense chemical weathering resulting in a laterite cover of varying thickness.
Beach sands, sand dunes and alluvium occurring along the low lying coastal area and narrow alluvial strips along rivers and streams are of sub-recent to recent age. Laterite constitutes the most widespread and important water bearing formation in the State.

Stratigraphic sequence of rock formations in Relief and Structure of Goa

Late Cenozoic to Recent- Sand, alluvium, lateritic soil and laterite
Upper Cretaceous to Lower Eocene – Deccan Trap volcanics and dolerite dykes
Early Proterozoic – Acidic and basic intrusives including granites, gabbros, dolerite dykes and ultramafics
Archean (3000-2500 Ma)-

Vageri Fm: Carbonate-quartz-chlorite schist and metagreywacke with some quartzite and metavolcanics
Bicholim Fm: Qtz-chlt-biotite schist, chert, Fe and Mn oxides, metabasalt, metagabbro, BIF, qtz-sericite schist, Mg- limestone
Sanvordem Fm: Quartzite, qtz-chlorite schist, metagreywacke with conglomerate
Barcem Fm: Metabasalt, metagabbro, metaacid volcanics, quartzite, qtz-chlorite schist

Archean (>3000 Ma) –Basement Peninsular Gneiss

Physical Division of Relief and Structure of Goa

Goa as a region can be divided into four physical divisions-

The eastern hill region comprising areas in the western ghat like Sattari, Ponda, Cancona and Sanguem
The Central valley land comprising Pernem, Bicholim, Ponda, Eastern Sanguemand Quepem
The flood plains comprising the coastal plains and uplands
Coastal plains with the areas of Tiswadi, Murmugao, Bardez and Salcete.

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