Springshed Springshed Management Training Curriculum Management Training Curriculum Draft Version 2 January 2016 The Springs Initiative 2016 The Springs Initiative
SESSION TITLE: Mapping Springs in Crystalline Terrain Eastern Ghats, Southern Western Ghats, & Granitic Zones SECTION: Understanding the Resource MODULE: III. Springshed Mapping AUTHORS: Dr Jared Buono CONTRIBUTING ORGANIZATIONS: Arghyam, Acwadam PURPOSE: Mapping in crystalline igneous zones requires a specific approach relative to other areas IMPACT: Participant will be able to identify and map important hydrological features in igneous intrusive areas TIME REQUIRED: 60 minutes MATERIALS: This ppt ADDITIONAL RESOURCES:
Outline: Defining crystalline terrain Reviewing igneous intrusive genesis, structures, features Landscape examples Hydrogeology of crystalline areas Regolith and fracture zone aquifer contributions Relationship to springs Guidance for mapping springsheds in these areas
Mapping & Management of Springs in Crystalline Terrain Eastern Ghats, Southern Western Ghats, & Granitic Zones
Photo: Luis Fernández García, Wikimedia Commons Crystalline terrain Refers to areas composed of rocks with crystals Can focus on intrusive igneous rocks granite, charnockite, diorite, etc Pertinent to Eastern Ghats and southern Western Ghats, but also granitic areas in Meghalaya and elsewhere
Igneous Intrusion - Formation Currents in the molten interior of the earth Hot, liquid plumes move up through crust Nearing the surface they cool Slow cooling allows differentiation in minerals large crystal Larger the crystals the slower the cooling time Credit: Wikimedia Commons, User: Woudloper
Photo: Wikimedia Commons Crystalline terrain Can form hummocky or hilly terrain Mainly intrusive structures: laccoliths, batholiths But may include more complex geology with dykes, sills, local metamorphics, etc Photo: a granitic intrusion in Karnataka
Igneous Structures Structures: A = active magma chamber (called pluton when cooled and entirely crystallized; a batholith is a large rock body composed of several plutonic intrusions) B = old magmatic dykes/dikes C = emerging laccolith D = old pegmatite (late-magmatic dyke formed by aggressive and highly mobile residual melts of a magma chamber) E = old and emerging magmatic sills F = stratovolcano Credit: Wikimedia Commons, User: Woudloper
Igneous Structures Accompanied processes: 1 = young subvolcanic intrusion cutting an older one 2 = xenolith (solid rock of high melting temperature transported within magma from below) or roof pendant (fragment of the roof of the magma chamber that has detached and sunk into the melt) 3 = contact metamorphism in the country rock 4 = uplift at the surface due to a laccolith Credit: Wikimedia Commons, User: Woudloper
Crystalline hydrogeology Aquifer dominated by regolith and fractured crystalline rock Regolith is the weathered top of the rock formation, consisting of soil, organic material and decomposed parent rock Fractures and joints are those occurring in the crystalline rock, below the regolith Post-cooling, fractures are formed by tectonic activity and joints by unloading of pressure Also in associated features such along dykes and sills
Crystalline hydrogeology Aquifer components dominated by regolith and fractured crystalline rock Regolith is the weathered top of the rock formation, consisting of soil, organic material and decomposed parent rock including: Saprolite, in-situ weathering of igneous rock, high clay accumulation Laterite, more highly weathered, porous, red in color Fractures and joints are those occurring in the crystalline rock, below the regolith Post-cooling, fractures are formed by tectonic activity and joints by unloading of pressure Also in associated features such along dykes and sills
Hydrogeology Components: Regolith can be 0 30 meters deep Bedrock often exposed in high topography Fractured bedrock - extent of fractures and joints highly variable, decreases with depth Credit: USGS
Hydrogeology Regolith and fractures both store and transmit groundwater Connect recharge and discharge areas Most of the initial capture of water occurs in the regolith Most of the storage may occur here too depending on depth of weathering and extent of fracture systems Fracture systems, dykes and other lineaments may act more as conduit than main storage component
Hydrogeology Regolith has porosity between 30-50%, decreases with depth Fracture zones usually much less than 10%, more likely to be 1% Solely secondaryporosity Credit: USGS
Hydrogeology Relative storage volumes: Regolith acts as sponge that absorbs rainfall Storage occurs in regolith Also acts to slowly feed fractures and joints Credit: USGS
Hydrogeology Springs may drain from regolith Or fractures and joints Mainly fracture, depression and contact type springs are seen Credit: USGS
Photo: Wikimedia Commons Credit: Wikimedia Commons, User Adityamadhav83 Mapping Measuring depth of regolith Mapping extent and orientation of fractures & joints
Photo: Wikimedia Commons Credit: Wikimedia Commons, User Adityamadhav83 Mapping Measuring depth of regolith Mapping extent and orientation of fractures & joints Hilltops 2 meters of laterite Slopes 0.5 meters of soil Fractures large, vertically oriented, running NE-SW Valley Floor 10 meters soil, alluvium & weathered rock Joints occasional, horizontal, short length Hilltop Valley Floor Slope
Mapping a springshed Field survey: Start at springs and transect walk up and downslope, valley-to-valley Record any geologic structures or features Included outcrops, changes in rock type, fractures Measure depth of regolith (use wells, road cuts or pits when needed) Surveys may also include less intuitive features such as changes in slope, abrupt changes in vegetation, streams, wells, etc At each feature record location and elevation via GPS Can map directly on toposheet or later upload to google earth (see session on section mapping in this module)
Mapping a springshed Satellite survey: Use google earth/maps to find spring Mark features from field survey Add any new features not found on field survey Conduct drainage density mapping (see sessions on drainage density, google mapping & using google earth in this module) Combine field and satellite surveys Create one map with all features Convert surface to vertical profile, and then to 3D conceptual model (see sessions on vertical profiles, & mapping in Himalayas, Western Ghats)
Mapping a springshed Combine field and satellite surveys Satellite survey: Use google earth/maps to find spring Mark features from field survey Add any new features not found on field survey (see sessions on section mapping, & mapping in Himalayas, Western Ghats)