Goa: Relief and Structure | Goa State PSC (GPSC) Preparation - GPSC (Goa) PDF Download

Relief and Structure of Goa

• Goa is predominantly covered by rocks from the Goa Group, a part of the Dharwar Super Group, with the exception of a small section in the northeast occupied by Deccan Trap formations from the Upper Cretaceous-Lower Eocene period.
• The Goa Group comprises green schist, a type of metamorphic rock, divided into distinct formations such as Barcem, Sanvordem, Bicholim, and Vageri in successive layers.
• In the northeastern corner, the Deccan Trap region exhibits sporadic laterite deposits along with the primary rock formations.
• Iron and manganese are the primary minerals of economic significance found in the region.
• Situated within the larger Konkan area, Goa features diverse topography, including hills, lowlands, plateaus, and mountainous areas.

Physical Features of Relief and Structure of Goa

• Goa shares geographical similarities with its neighboring states, Maharashtra and Karnataka.
• The state's physical geography can be categorized into three main divisions:
  • Mountainous Region: Located in the east, this area is defined by the Sahyadri Ranges with an average elevation of 800 meters. Major peaks in this region include Sonsagar, Vaguerim, Morlemchogor, and Catlanchimauli. Most of Goa's rivers originate from this mountainous region.
  • Plateau Region: Situated in the central part of the state, the plateaus have altitudes ranging from 30 to 100 meters. The Mandovi and Zuari rivers are significant in draining this area.
  • Low-lying River Basins and Coastal Plains: These areas have rivers like Chapora, Sal, Kushavati, Baga, Tiracol, Talpona, Mandovi, Zuari, and Galgibagh. The basins near the coast are fertile for agriculture.

Low Lands of Relief and Structure

• The low land area of Goa primarily comprises coastal regions stretching approximately 110 km.
• Abundant beaches adorn this coastal stretch, enhancing its natural beauty and appeal.
• Several rivers traverse this area from the east to the west, enriching the land and making it fertile for cultivation.
• Due to its fertility and favorable conditions, the lowlands are densely populated.

Plateau Lands of Relief and Structure

• Situated between the mountainous east and the lowlands in the west, the plateau lands of Goa exhibit heights ranging from 30 to 100 meters.
• Noteworthy for its abundance of laterite stones, this region utilizes these stones for constructing houses, showcasing the resourcefulness of its inhabitants.
• Some areas within the plateau lands are identified as headlands, where lighthouses stand as beacons for maritime navigation.
• While the plateau lands do not boast fertile soil, certain crops can still be cultivated in this region.

Mountain region of Relief and Structure of Goa

• Sahyadri Mountains: Located to the east of South Goa.
• Forest Cover: This region is covered with dense forests, with some mountains being very steep.
• Peaks in South Goa: Includes Chandranath at Paroda, Dudhsagar in Sanguem taluka, and Cormolghant in Canacona taluka.
• Rivers: Several rivers flow from this region to the lowlands, including Zuari, Talpona, Sal, and Galgibag.
• Transportation: Rivers are used for transportation.
• Inland Waterways: Important for transporting mineral ores from mining sites in Sanguem taluka (such as Costi, Kirpal, Netravalim, Rivona, Ducorcond, and Kuddegal) to Mormugao Harbour for export.
• Natural Resources: South Goa is rich in resources like trees, iron, and manganese ore, which are mainly exported to Japan, South Korea, and some European countries.

General Geological Setup of Relief and Structure of Goa

• Understanding the regional and local geology is crucial for grasping the hydrogeological characteristics of an area.
• Groundwater occurrence and movement are influenced by the openings within rock formations.
• The type of rock, the extent of rock deformation, and the degree of weathering are key factors in determining rock porosity.
• Goa is situated on the Western Dharwar Craton, extending from the greenstone-granitoid terrain of Karnataka.
• This region includes rocks from the Peninsular Gneissic Complex (PGC) and the Dharwar Supergroup, both of Precambrian age.
• The PGC is prominently exposed along the Western Ghats in North Goa and around Chauri and Quepem in South Goa.
• The Dharwar Supergroup rocks in Goa are part of the northern extension of the Shimoga schist belt, known locally as the Goa Group.
• The PGC and Goa Group rocks have been intruded by mafic-ultramafic complexes, younger granites, and mafic intrusives.
• In the northeastern part of Goa, the Deccan Traps from the late Cretaceous to lower Eocene age cover a narrow strip.
• Many of these rocks are concealed beneath a thick layer of weathered laterite and soil of varying depths.
• The oldest rock in Goa is the Anmod Ghat Trondhjemitic Gneiss.
• The Peninsular Gneisses are grey, medium to coarse-grained, and banded or migmatitic, transitioning from Tonalite to Trondhjemite to Granodiorite.
• These gneisses form the basement for the Goa Group of rocks.
• The Goa Group comprises meta-volcanic and metasedimentary rocks, including greywackes, argillites, tuffs, agglomerates, mafic lavas, and banded iron formations.
• These rocks have undergone greenschist facies regional metamorphism and are similar to the Chitradurga Group of Karnataka.
• The Goa Group is divided into four formations: Barcem, Sanvordem, Bicholim-Rivona, and Vageri, in ascending order.
• The PGC and Goa Group rocks have been intruded by the Bondla mafic-ultramafic complex and granites, including the Canacona Granite and Dudhsagar Granite.
• These are followed by mafic intrusives.
• Overlying these rocks are the Deccan Traps, consisting of horizontal basaltic lava flows.
• In the late Cenozoic period, the rocks experienced intense chemical weathering, resulting in a varying thickness of laterite cover.
• Coastal areas and narrow alluvial strips along rivers and streams feature beach sands, sand dunes, and alluvium of sub-recent to recent age.
• Laterite is the most widespread and significant water-bearing formation in Goa.

Stratigraphic sequence of rock formations in Relief and Structure of Goa

• Late Cenozoic to Recent: Includes sand, alluvium, lateritic soil, and laterite.
• Upper Cretaceous to Lower Eocene: Comprises Deccan Trap volcanics and dolerite dykes.
• Early Proterozoic: Features acidic and basic intrusives such as granites, gabbros, dolerite dykes, and ultramafics.
• Archean (3000-2500 Ma):
  • Vageri Formation: Consists of carbonate-quartz-chlorite schist, metagreywacke, some quartzite, and metavolcanics.
  • Bicholim Formation: Includes quartz-chlorite-biotite schist, chert, iron and manganese oxides, metabasalt, metagabbro, banded iron formation (BIF), quartz-sericite schist, and magnesium limestone.
  • Sanvordem Formation: Contains quartzite, quartz-chlorite schist, metagreywacke, and conglomerate.
  • Barcem Formation: Comprises metabasalt, metagabbro, meta-acidic volcanics, quartzite, and quartz-chlorite schist.
• Archean (>3000 Ma): The basement is composed of Peninsular Gneiss.

Physical Division of Relief and Structure of Goa

Goa can be categorized into four physical divisions:

• Eastern Hill Region: Includes areas in the Western Ghats such as Sattari, Ponda, Cancona, and Sanguem.
• Central Valley Land: Encompasses Pernem, Bicholim, Ponda, Eastern Sanguem, and Quepem.
• Flood Plains: Covers the coastal plains and uplands.
• Coastal Plains: Consists of Tiswadi, Murmugao, Bardez, and Salcete.