Engineering Geology

1. INTRODUCTION Of Geology

• Introduction

Geology: Geology is the science that deals with various aspects of the Earth as a planet, grouped under earth science. The term comes from “Geo” meaning Earth and “logy” meaning science. It involves studying the Earth’s physical structure, substances, history, and the processes acting on them. Geology helps us understand the world around us and enables scientists to predict how planets will behave. For example, as populations grow, more people live in areas prone to hazards like floods and landslides. Studying geology is crucial to prevent such disasters by understanding their history and predicting future occurrences.

Engineering Geology: This branch of applied science focuses on using geological knowledge for the safe, stable, and economical design and construction of civil engineering projects.

• Branches of Geology

1. Physical Geology: Studies the structure of rock bodies and large bodies of water and ice. It deals with internal agents like volcanism and earthquakes, and external agents like wind, water, ice, and the atmosphere.
2. Geomorphology: Examines the Earth’s surface features such as mountains, plains, plateaus, valleys, and basins.
3. Mineralogy: Focuses on the formation, occurrence, properties, and uses of minerals.
4. Petrology: Studies the formation, occurrence, composition, texture, and distribution of rocks.
5. Economic Geology: Investigates minerals and rocks that can be exploited for human benefit.
6. Geography: Studies the Earth’s physical features, atmosphere, and human activities affecting and affected by these features.
7. Geophysics: Applies physics to solve geological problems like geomagnetism and geo-electrolyze.
8. Geochemistry: Deals with the Earth’s chemical composition.
9. Geodetic: Involves land surveying.
10. Climatology: The scientific study of climate.
11. Meteorology: The study of the atmosphere and weather.
12. Oceanography: Studies the oceans.
13. Paleontology: The study of ancient life through fossils.
14. Hydrogeology: Focuses on groundwater and surface water processes.
15. Crystallography: Studies the external and internal forms of crystalline minerals.

• Interrelationships Between Branches Of Geology

1. Geology and physics: Geophysics is essential for exploring oil and other minerals. For example, in Nepal, seismic studies help understand the nature of rock layers beneath the Earth’s crust by analyzing changes in seismic wave velocities.
2. Geology and chemistry: Geochemical studies help understand chemical weathering in rocks and the decay of radioactive elements, aiding in age determination.
3. Crystallography: This branch involves studying the atomic structure of crystals, which is crucial for understanding mineral properties.
4. Geodetic: Helps measure geological features, calculate distances, gradients of hills, and elevations, which is vital for projects in Nepal’s mountainous regions.

 

5. Oceanography: Oceans play a significant role in forming geological features and influencing plate tectonics and geological processes.

• Scope, Objectives, and Importance of Geology in Civil Engineering
• Scope of Engineering Geology:

1. In construction work: Geological information is crucial for planning, designing, and constructing buildings, dams, reservoirs, highways, bridges, tunnels, and retaining structures. In Nepal, this knowledge is vital for safe and economical construction in diverse terrains.

• Planning
• Topographic maps:

1. Essential for understanding the merits and demerits of relief features.
2. Helps in assessing the nature of slopes and depth of valleys.
3. Allows easy computation of elevation changes in various directions.

• Hydrological maps:

Shows surface and subsurface water channels, their occurrence, and depth.

• Geological maps:

Indicates rock types and their distribution.

• Design

1. Structural disposition of rocks.
2. Materials of construction.
3. Exploratory operations (e.g., test holes).
4. Subsurface investigation.
5. Identifying the existence, depth, and inclination of hard bedrocks.
6. Assessing the mechanical properties of rocks, such as compressive, shear, and transverse strength, modulus of elasticity, permeability, and resistance to decay.

• Construction

1. Quality control of construction materials like sand, gravel, crushed rocks, and soil.
2. Applications include mining works, tunneling, wetland habitat restoration, government and military installations, river control, and shipping work.
3. Knowledge is crucial for constructing dams, designing foundations, highways, and tunnels, and analyzing soil properties.

• Objectives of Geology in Civil Engineering

1. Study the stability of rock masses and slopes.
2. Predict changes in the Earth’s surface over time.
3. Understand the hydrological and mechanical behavior of rock masses.
4. Study environmental changes and their consequences.
5. Elaborate on geomorphology, lithography, stratigraphy, and groundwater conditions.
6. Evaluate the mineralogical, physio-geomechanical, chemical, and hydraulic properties of earth materials involved in construction.

• Importance of Geology in Civil Engineering
• Locating natural resources.
• Assisting in flood control and other natural disaster management.
• Providing clues about ancient human settlements.
• Understanding environmental evolution and adaptation.
• Studying soil profiles, characteristics, and strength.
• Knowledge of the hydrological cycle, climatic conditions, and living and non-living things at a site.
• Understanding the origin and structure of the Earth.
• Selecting sites for civil engineering projects.
• Studying geological hazards.
• Locating thrusts, folds, faults, etc., and suggesting measures for construction in such zones.
• Definition of Engineering Geology According to IAEG

According to IAEG, “Engineering geology is the science devoted to investigating, studying, and solving engineering and environmental problems arising from the interaction between geology and human activities, as well as predicting and developing measures for the preservation or remediation of geological hazards.”

• Role of Engineering Geologists

Engineering geologists interpret landforms and earth processes to identify potential geologic and man-made hazards that may impact civil structures and human development. They are trained in geology and often have specialized education in soil mechanics, rock mechanics, geotechnics, groundwater, hydrology, and civil design. This unique combination of skills helps them mitigate hazards associated with earth-structure interactions.

• Importance of Engineering Geology in Nepal

The Himalayas, especially the Nepal Himalaya, are highly fragile and delicate. Due to extreme climatography, topography, and recent human expansion, the region is vulnerable to natural calamities like floods and landslides. The Himalayan range, formed by the collision of the Tibetan and Indian plates, is the most active tectonic zone, known for its complex structural deformations. This makes Nepal prone to various geohazards and instabilities, particularly landslides and debris flows.

2. BASIC REVIEWS OF THE EARTH

• Introduction

Earth:

• The third planet from the sun and the only known object in the universe to harbor life.
• Formed over 4.5 billion years ago, as evidenced by radiometric dating.
• Earth’s gravity interacts with other objects in space, especially the sun and the moon, its only natural satellite.
• Revolves around the sun in 365.25 days, known as an Earth year.

Earth and other planets are believed to have formed from a solidified cloud of dust and gases left over from the creation of the sun. Initially, the Earth’s interior remained solid and relatively cool.Over millions of years, radioactive decay of elements like uranium, thorium, and potassium released energy, causing the Earth’s constituents to melt. Iron, being heavier, sank towards the center, forming the core, while silicates formed the crust.

• Major Components of the Earth System

1. Atmosphere:
2. Surrounds the Earth in layers.
3. Protects life from direct solar radiation.
4. Gases in the atmosphere participate in cycles, with the carbon cycle being the most important.
5. Hydrosphere:
6. Includes all water on Earth’s surface: oceans, lakes, rivers, aquifers, and ice.
7. Covers 70% of Earth’s surface.
8. Lithosphere:
9. Covers the remaining 30% of Earth’s surface.
10. Thickness ranges from 0 to 40 km.
11. Biosphere:
12. Encompasses all life on Earth, including parts of the atmosphere, lithosphere, and hydrosphere.
13. Biodiversity varies with distance from the equator, being greater closer to the equator.

• Earth’s Internal Structure

Understanding Earth’s interior is crucial for studying plate tectonics. Seismic studies reveal three well-defined layers: crust, mantle, and core.

1. Crust:
2. Two types: thin oceanic crust (basalt) and thicker continental crust (granite).
3. The low density of continental crust allows it to float on the denser mantle.
4. Mantle:
5. Composed of olivine-rich rocks.
6. Temperature increases with depth, known as the geothermal gradient.
7. Divided into the upper mantle (cool and brittle) and lower mantle (hot and soft).
8. Core:
9. Composed mainly of iron and nickel alloy.
10. Source of Earth’s internal heat due to radioactive decay.
11. Divided into a liquid outer core and a solid inner core, with the inner core remaining solid due to immense pressure.

• Geological time scale

The Geological Time Scale (GTS) is a system of chronological dating that relates geological strata to time, used to describe the timing and relationship of events in Earth’s history.

Major Evolutionary Events:

• Quaternary Period: Evolution of humans.
• Tertiary Period: Evolution of mammals, flora, and fishes.
• Cretaceous Period: First flowering plants, extinction of dinosaurs.
• Jurassic Period: First birds appeared, diversification of dinosaurs.
• Mountains

A mountain is any landmass higher than the surrounding area. Structures up to 700 meters are called hills, while those with greater relief are mountains.

• Types of Mountains

1. Mountain Range: A series of mountains formed during the same geological period.
2. Mountain System: A group of mountain ranges of the same geological age.
3. Mountain Chain: A series of mountain systems of different geological ages.

• Classification by Origin

1. Tectonic mountains: Formed due to internal forces within the Earth, usually at convergent plate boundaries. The Himalayas are a prime example.
2. Volcanic mountains: Formed by volcanic eruptions, e.g., Mt. Fuji.
3. Fault mountains: Formed by the displacement of Earth’s crust along fault lines. The upthrown part is called a horst, and the downthrown part is called a graben.
4. Fold mountains: Formed by the folding of Earth’s crust when two plates collide, e.g., the Rockies.
5. Residual mountains: Formed by the erosion of softer materials, leaving behind more resistant rocks.

• Shields

A shield is a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks, forming tectonically stable areas. These rocks are often over 570 million years old, sometimes dating back 2 to 3.5 billion years. The Canadian Shield is an example.

• Plateaus

A plateau is a land area with a relatively level surface, raised above adjoining land on at least one side, often cut by deep canyons. Plateaus have a larger summit area than mountains.

• Formation of Plateaus

1. Volcanicactivity:g., the Columbia Plateau in the U.S.
2. Erosion: By glaciers, water, and wind.

• Types of Plateaus

1. Intermontane Plateaus: Surrounded by mountains, e.g., the Tibetan Plateau.
2. Piedmont Plateaus: Bordered by mountains on one side and plains or seas on the other.
3. Continental Plateaus: Bordered by plains or oceans, away from mountains.

• Plate Tectonics

Plate tectonics involves the movement and interaction of Earth’s plates. The Earth’s crust is divided into seven large plates and several smaller ones, which move around on the semi-molten mantle due to convection currents.

1. Major Plates
2. Pacific Plate
3. North American Plate
4. South American Plate
5. African Plate
6. Eurasian Plate
7. Indo-Australian Plate
8. Antarctic Plate
9. Philippine Plate
10. Caribbean Plate
11. Nazca Plate
12. Cocos Plate
13. Arabian Plate

• Plate Boundaries

1. Convergent Boundaries: Plates move towards each other, causing one to subduct beneath the other. This can form mountain ranges, e.g., the Himalayas.
2. Divergent Boundaries: Plates move away from each other, creating mid-ocean ridges, e.g., the boundary between the North American and Eurasian plates.
3. Transform Fault Boundaries: Plates slide past each other horizontally, e.g., the San Andreas Fault in California.
4. CRYSTALLOGRAPHY AND MINERALOGY

• Introduction

Crystallography: The branch of science that studies the external form and internal atomic structure of crystalline structures.

Crystal: A homogeneous solid bounded by naturally formed plane faces, related to a regular internal arrangement of atoms. The process of forming crystals from liquid, gaseous states, or by precipitation from solution is called crystallization.

• Arrangement of Atoms in Crystals

Crystals are orderly assemblages of atoms or groups of atoms arranged in a three-dimensional pattern, repeated throughout the crystal. The unit cell is the smallest complete unit of this pattern, and the whole crystal structure can be thought of as unit cells stacked together. The symmetry of this unit determines the external symmetry of the crystal. The arrangement of atoms or ions in the crystal can be shown by the framework of the space lattice.

• Elements of Crystal

1. Interfacial Angles: The angle between adjacent faces of a crystal. Measured using a contact goniometer.
2. Crystallographic axes: Also known as axes of reference. Mathematical relationships exist between the crystal faces. Faces can be referred to three coordinate axes passing through the center of the crystal.
3. Axial ratio: The relationship between the lengths of different crystallographic axes in a given crystal.
4. Crystal face: External surfaces of a crystal, which may be regular or modified geometrical figures like squares, rectangles, triangles, etc.

• Symmetry Elements of Crystal

Symmetry elements help visualize the symmetry of an ordered arrangement in a crystal:

Axis of Symmetry: An imaginary line through the center of a crystal. When the crystal is rotated, similar faces appear at least twice.

• Two-fold Symmetry: Two similar faces appear.
• Three-fold Symmetry: Three similar faces appear.
• Four-fold Symmetry: Four similar faces appear.
• Six-fold Symmetry: Six similar faces appear.
• Plane of Symmetry: An imaginary line dividing the crystal into two symmetrical halves, each being a mirror image of the other.
• Center of Symmetry: The midpoint of the line joining two identical points on opposite faces of the crystal.
• Crystal form

A form consists of a group of crystal faces with the same relation to the symmetry elements:

1. Pedion: Single face.
2. Pinacoid: Two parallel faces on opposite sides.
3. Prism: Three or more non-parallel faces symmetrical about an axis.
4. Pyramid: Three or more non-parallel faces intersecting at a common point.
5. Dipyramid: Combination of two pyramids.
6. Scalenohedron: Faces with scalene triangle geometry.
7. Rhombohedron: Faces with rhombus geometry.

• Crystal Habit

The general shape of a crystal, influenced by the conditions during its formation:

1. Acicular: Needle-like, e.g., Natrolite.
2. Bladed: Knife-like flat blades, e.g., Kyanite.
3. Fibrous: Fine thread-like strands, e.g., Gypsum, Asbestos.
4. Foliated: Thin, separate lamellae or leaf shapes, e.g., Mica.
5. Lamellar: Separable plates or leaf shapes, e.g., Wollastonite.
6. Prismatic: Elongated in one direction, e.g., Feldspars.
7. Reticulated: Cross-mesh pattern.

• Crystal Systems

Crystals are classified into seven systems based on their symmetry elements:

1. Isometric (cubic) system: All sides equal, all angles 90°, e.g., Galena, Garnet.
2. Tetragonal System: Two horizontal axes equal, vertical axis unequal, all angles 90°, e.g., Chalcopyrite.
3. Orthorhombic System: All axes unequal, all angles 90°, e.g., Barytes, Aragonite.
4. Hexagonal System: Four axes, three equal horizontal axes intersecting at 60°, one vertical axis unequal, e.g., Quartz, Calcite.
5. Trigonal System: Similar to hexagonal but with different symmetry, e.g., Quartz, Calcite.
6. Monoclinic System: All axes unequal, two angles 90°, one angle not 90°, e.g., Feldspar, Gypsum.
7. Triclinic System: All axes unequal, all angles not 90°, e.g., Kyanite, Turquoise.

• Mineralogy

Mineralogy is the branch of geological science that deals with the study of various aspects of minerals, including their origin, properties, composition, and classification.

Minerals: Naturally occurring inorganic substances with a definite chemical composition in a crystalline state.

• Identification of Minerals

Minerals can be identified based on their physical, chemical, and optical properties.

1. Physical Properties: External appearance of minerals.
2. Chemical Properties: Chemical composition of minerals.
3. Optical Properties: Properties observed when light passes through minerals in thin sections under a polarizing microscope.

• Physical Properties

Each mineral has distinct qualities that differentiate it from others, such as shape, color, shine, and hardness.

1. Color: The appearance of a substance in light, depending on its composition and structure.
2. Inherent Color: Due to chemical composition, diagnostic.
3. Exotic Color: Due to small traces of impurities.
4. Luster: The way minerals reflect light from their surface.
5. Metallic Luster: Shines like metal (e.g., silver, gold).
6. Non-metallic Luster: Includes pearly, silky, adamantine, vitreous, resinous, and earthy.
7. Streak: The color of a mineral in powdered form.
8. Transparency: The ability of light to pass through a mineral.
9. Transparent: Light passes fully (e.g., quartz).
10. Semi-transparent: Light passes partially (e.g., calcite).
11. Translucent: Only some diffused light passes (e.g., sulfur).
12. Opaque: No light passes through (e.g., orthoclase).
13. Hardness: The resistance of a mineral to scratching, measured using Mohs hardness scale.

• Mohs Hardness Scale:

Hardness	Mineral	Example Use
1	Talc	Baby powder
2	Gypsum	Plaster of Paris
3	Calcite	Limestone and marble
4	Fluorite	Fluorine source
5	Apatite	Fertilizer
6	Orthoclase	Feldspar in ceramics
7	Quartz	Glass making
8	Topaz	Gemstones
9	Corundum	Abrasives
10	Diamond	Cutting tools and jewelry

1. Cleavage: The tendency of minerals to break along certain planes, producing smooth surfaces.
2. Fracture: The surface obtained by breaking in a direction other than the cleavage plane.

Types: Conchoidal, even, uneven, hackly, splintery, earthy.

1. Tenacity: The resistance of a mineral to breaking, crushing, bending, and tearing.

Types: Brittle, ductile, malleable, flexible, elastic.

1. Specific Gravity: The ratio of the weight of a mineral to the weight of an equal volume of water at 4°C.

• Optical Properties

These properties are studied under a polarizing microscope and help in the precise identification of minerals.

• Chemical Properties

Minerals have definite chemical compositions, which can be determined through detailed chemical analysis.

• Classification of Minerals

Minerals are classified into two groups based on their silica content:

1. Silicate Minerals: Contain silica tetrahedrons.
2. Feldspar Group:g., plagioclase feldspar (NaAlSi₃O₈), orthoclase.
3. Pyroxene Group:g., augite.
4. Hypersthene:g., (Mg, Fe)SiO₃.
5. Amphibole Group:g., hornblende.
6. Mica Group:g., biotite.
7. Non-silicate Minerals: Do not contain silica tetrahedrons.
8. Oxides:g., hematite.
9. Carbonates:g., calcite.
10. Sulfides:g., pyrite.
11. Halides:g., halite, fluorite.
12. Sulfates:g., barite, gypsum.

• Miscellaneous:g., graphite, diamond, gold (Au), sulfur (S).
• Rock-Forming Minerals

Mineral	Color	Streak	Luster	Hardness	Special Properties
Biotite	Black, dark gray	White	Vitreous	2.5-3	None
Calcite	Colorless, white	White	Vitreous	3	Effervescent in acid
Corundum	Reddish pink, blue	None	Vitreous	9	None
Fluorite	Variable	White	Vitreous	4	None
Gypsum	Colorless, white	White	Silky to Vitreous	2	None
Halite	Colorless, white	White	Vitreous	2.5	Salty taste
Magnetite	Black, dark gray	Black	Metallic	5.5-6.5	Magnetic
Muscovite	Clear, white	White	Vitreous	2-2.5	None
Olivine	Green to yellow-green	None	Vitreous	6.5-7	None
Plagioclase	White, sometimes blue	White	Vitreous	6-6.5	None
Pyrite	Brassy yellow	Dark gray	Metallic	6-6.5	None
Quartz	Colorless, various	White	Vitreous	7	None

 

4. PETROLOGY

• Introduction: Petrology, Petrography, Petrogenesis

Petrology: A branch of geology that deals with the study, origin, composition, distribution, and structure of rocks. (From Greek: petra = rock, logos = explanation)

Aim: To understand the geologic system in which a body of rock originates.

Importance: Provides insights into the history of our planet.

Branches:

Petrography: Describes and classifies rocks, especially through microscopic examination of thin sections.

Petrogenesis: Studies the origin and evolution of rocks, particularly igneous rocks.

• Rock & Rock Cycle

Rock: Naturally occurring aggregates of minerals.

Types:

1. Monomineralic Rock: Composed of only one mineral.
2. Multimineralic Rock: Composed of more than one mineral.

Traditional Classification of Rocks:

1. Igneous Rock
2. Metamorphic Rock
3. Sedimentary Rock

• Other Terms:

Stone: A piece or block of rock detached from the rock mass.

Boulder: A large piece of rock with a diameter greater than 256 mm.

• Rock Cycle: Rocks are continuously subjected to change and can transform into other types through geological processes.

Processes:

1. Weathering: Breaks down rocks into sediments.
2. Metamorphism: Transforms rocks through heat and pressure.
3. Melting: Forms magma, which solidifies into igneous rocks.

• Classifications, Structures, Textures of Rocks

1. Classification of Rocks:
2. Igneous Rocks
3. Sedimentary Rocks
4. Metamorphic Rocks
5. IGNEOUS ROCKS:

• Formation: Solidification of magma either below, on, or above the Earth’s surface.
• Types:

1. Intrusive Rocks: Formed by slow cooling of magma inside the Earth, resulting in coarse-grained texture (e.g., Granite, Pegmatite, Gabbro, Diorite).
2. Extrusive Rocks: Also called volcanic rocks, formed by rapid cooling of lava on or above the Earth’s surface, resulting in fine-grained texture (e.g., Basalt, Rhyolite).
3. Chemical Classification of Igneous Rocks:
4. Acidic Rock: Silica content > 66% (e.g., Granite)
5. Intermediate Rock: Silica content 52-66% (e.g., Diorite)
6. Basic Rock: Silica content 45-52% (e.g., Gabbro)
7. Ultrabasic Rock: Silica content < 45% (e.g., Peridotite)

• Mineral Composition:

1. Essential Minerals: Necessary for naming or identifying rocks (e.g., Quartz, Feldspar).
2. Accessory Minerals: Presence or absence doesn’t change the rock’s definition (e.g., Zircon, Apatite).

• Secondary Minerals: Formed due to weathering, metamorphism, or precipitation (e.g., Limonite, Chlorite, Calcite).
• Types of Igneous Rocks Based on Mineral Content:

1. Felsic Rocks: Contain light-colored minerals like silica, feldspar, and muscovite.
2. Mafic Rocks: Contain dark-colored minerals like pyroxene and olivine.
3. Intermediate Rocks: Have a mix of light and dark minerals.
4. Ultramafic Rocks: Contain very high amounts of dark minerals.

• IUGS Classification of Igneous Rocks

QAP Diagram: Used to classify plutonic rocks based on the percentage of Quartz (Q), Alkali Feldspar (A), and Plagioclase (P).

• Important Features of Igneous Rocks

1. Generally hard, massive, and compact with interlocking grains.
2. Absence of fossils.
3. Absence of bedding planes and foliation planes.
4. Enclosing rocks are baked.
5. Usually contain much feldspar.

• Structures of Igneous Rocks

Structure	Description
Vesicular Structure	Formed by escaping gases, creating empty cavities (vesicles).
Amygdaloidal Structure	Vesicles filled with secondary minerals like calcite and zeolites.
Columnar Structure	Polygonal cracks formed during cooling, common in basalt.
Flow Structure	Alternating bands or layers of differing composition, crystallinity, texture.
Pillow Structure	Discontinuous pillow-shaped masses, common in extrusive rocks.
Orbicular Structure	Ball-like aggregations with concentric shells of different minerals.

• Forms of Igneous Rocks

Form	Description
Concordant Bodies	Magma solidifies parallel to the bedding/foliation of existing rock.
Discordant Bodies	Magma cuts across the bedding/foliation plane of existing rock.

• Types of Concordant Bodies:

Sill: Magma solidifies in the form of a thin sheet within existing bedding/foliation.

Phacolith: Magma solidifies in the crests or troughs of folds under low pressure.

Laccolith: Magma forms a dome or arch by pushing rock layers upward due to high viscosity.

Lopolith: A body with a flat top and convex base, often with a feeder pipe below.

• Uses of Different Igneous Rocks

Igneous Rock	Nepali Name	Uses
Granite	ग्रेनाइट	Building material, countertops, monuments, and decorative stone.
Basalt	बेसाल्ट	Road base, concrete aggregate, asphalt pavement, and construction stone.
Pumice	प्यूमिस	Abrasive material, lightweight concrete, and landscaping.
Obsidian	ओब्सिडियन	Cutting tools, surgical instruments, and decorative items.
Diorite	डियोराइट	Construction stone, decorative stone, and countertops.
Gabbro	गाब्रो	Construction aggregate, countertops, and decorative stone.
Andesite	एन्डेसाइट	Construction stone and decorative stone.
Rhyolite	राइओलाइट	Decorative stone and sometimes in construction.

1. Sedimentary Rocks

• Formation: Sedimentary rocks are formed through the process of sedimentation, which involves the accumulation, compaction, cementation, and consolidation of sediments derived from the weathering of older rocks. Geologic agents like water, wind, and ice play a crucial role in this process.
• Sedimentation Process

1. Compaction: Decrease in volume due to the weight of overlying sediments.
2. Lithification: Transformation of loose sediments into solid rock.
3. Petrification: Conversion of organic material into a stony substance.
4. Cementation: Binding of sediments with fine materials.

• Diagenesis

Diagenesis: Includes cementation, compaction, and the growth of minerals.

• Classification of Sedimentary Rocks

Sedimentary rocks can be classified based on their mode of formation into two main types: Clastic and Non-clastic rocks.

1. Clastic Rocks

Formed by mechanical sedimentation processes. Sediments are measured using the Phi scale, which indicates the size of sediments or clasts.

 

 

Sediment Size	Name
>256 mm	Boulder
64-256 mm	Cobble
16-64 mm	Pebble
2-16 mm	Gravel
2-1/16 mm	Sand
<1/16 mm	Clay

Types of Clastic Rocks:

1. Rudites (Rudaceous): Composed of coarse-grained clasts (e.g., Breccia, Conglomerates).
2. Arenites (Arenaceous): Composed of sand-sized particles (e.g., Sandstone).
3. Lutites (Argillaceous): Composed of fine-grained sediments (e.g., Shale, Claystone, Siltstone, Mudstone).
4. Non-clastic Rocks

Formed from chemical and biogenic sedimentation processes.

Types of Non-clastic Rocks:

1. Chemical Sedimentary Rocks:

Siliceous	Composed of silica (e.g., Chert).
Carbonate	Composed of carbonate (e.g., Limestone).
Ferruginous	Composed of iron.
Phosphatic	Composed of phosphate.
Evaporites	Formed from evaporation (e.g., Gypsum).

1. Biogenic or Organic Sedimentary Rocks:

Carbonate	Composed of calcareous material (e.g., Fossiliferous Limestone).
Carbonaceous	Composed of carbon (e.g., Coal).
Phosphatic	Composed of phosphate.
Ferruginous	Composed of iron.

• Structural Features of Sedimentary Rocks

1. Stratification: Layers of sedimentary rock separated by bedding planes.
2. Lamination: Thin layers (less than 1 cm) within a bed.
3. Graded Bedding: Gradation from coarse grains at the bottom to fine grains at the top.
4. Cross Bedding: Inclined layers formed by wind or water movement.
5. Ripple Marks: Formed by wind or water, indicating current direction.
6. Mud Cracks: Polygonal cracks formed by the drying of sediment.
7. Rain Prints: Shallow depressions caused by raindrop impacts.
8. Tracks & Trails: Marks left by animals or worms on soft sediment.

• Texture of Sedimentary Rocks

1. Clastic Texture:
2. Size of Grains:

Coarse-grained	>75 mm
Medium-grained	1-5 mm
Fine-grained	<1 mm

1. Shape of Grains:
2. Rounded
3. Sub-rounded
4. Angular

• Packing of Grains:

1. Openly packed
2. Compactly packed
3. Sorting of Grains:
4. Poorly sorted
5. Well sorted
6. Non-clastic Texture:

Macrocrystalline	Grains >20 micrometers.
Microcrystalline	Grains <20 micrometers.
Cryptocrystalline	Grains not visible under a microscope.

• Important Features of Sedimentary Rocks

1. Layers: They form in layers over time.
2. Fossils: Often contain remains of ancient plants and animals.
3. Porous: Have tiny spaces that can hold water, oil, or gas.
4. Grain Size: Can have fine or coarse grains.
5. Minerals: Some are made from minerals that settle out of water.
6. Color: Colors vary based on what they’re made of and how they formed.
7. Bedding Planes: Flat surfaces that separate each layer.

• Uses of Different Sedimentation Rock

Rock Name	नाम (नेपाली)	Uses
Sandstone	पत्रे चट्टान	Used in construction, making glass, and ceramics.
Limestone	चुनढुंगा	Used to make cement, building stones, and in the production of lime.
Coal	कोइला	Used as a fuel for electricity generation and in steel production.
Shale	शेल	Used in the production of bricks and cement.
Rock Salt	चट्टान नुन	Used in food seasoning and as a de-icing agent.
Gypsum	जिप्सम	Used to make plaster and drywall.
Conglomerate	कङ्गलोमेरेट	Used in construction and as decorative stones.

 

1. Metamorphic Rocks

• Formation: Metamorphic rocks form from existing sedimentary or igneous rocks under the influence of temperature and pressure. They are classified based on their origin:

1. Ortho-metamorphic rocks: Derived from igneous rocks.
2. Para-metamorphic rocks: Derived from sedimentary rocks.

The process of forming metamorphic rocks is called metamorphism, which can be categorized into four types:

1. Regional Metamorphism: Occurs on a large scale due to plate movements, such as the Himalayan metamorphism.
2. Contact Metamorphism: Happens when rocks come into contact with magma, with heat being the primary factor.
3. Cataclastic Metamorphism: Results from faulting and shearing friction, with dynamic pressure as the main factor.
4. Burial Metamorphism: Caused by the pressure and temperature of overlying beds.

• Examples of Metamorphism

Rock	Transforms to
Shale (sedimentary)	slate (low-grade metamorphic).
Limestone (sedimentary)	marble (metamorphic).
Sandstone (sedimentary)	quartzite (metamorphic).
Granite (igneous)	gneiss (metamorphic).

• Classification of Metamorphic Rocks

Metamorphic rocks are classified based on the presence or absence of structures indicating parallelism of the constituents:

1. Foliated Rocks: Have a platy or sheet-like structure with minerals aligned in parallel planes (e.g., slate, schist, gneiss).
2. Non-foliated Rocks: Lack a platy structure and typically contain one mineral (e.g., quartzite, marble).

• Structures in Metamorphic Rocks

1. Cataclastic Structure: Formed under severe crushing and shearing, characterized by fine grain size (e.g., crush breccias, slate).
2. Schistose Structure: Formed under intense stress, with parallel bands of flaky minerals (e.g., schist).
3. Gneissose Structure: Formed under directed pressure and heat, with alternating bands of different minerals (e.g., gneiss).
4. Maculose Structure: Characterized by a spotted appearance due to incomplete recrystallization (e.g., hornfels).
5. Augen Structure: Features lens-like shapes of resistant minerals formed under stress.
6. Granulose Structure: Formed by recrystallization under high temperature and pressure, found in rocks like quartzite and marble.

• Textures of Metamorphic Rocks

1. Crystalloblastic Texture: Formed by recrystallization of mineral grains.
2. Idioblastic: Crystals with perfect faces.
3. Xenoblastic: Crystals without definite faces.
4. Porphyroblastic Texture: Large crystals (idioblasts) embedded in a fine-grained matrix.
5. Granoblastic Texture: Granular or equidimensional major constituents.
6. Palimpsest Texture: Remnant texture of the parent rock preserved in the metamorphic rock.

• Rock Cleavage

Rock cleavage is the tendency of rocks to split along certain directions, yielding smooth surfaces. It can be:

1. Slaty Cleavage: Due to parallel arrangement of minerals, common in slate and phyllite.
2. Fracture Cleavage: Resembles closely spaced parallel joints or fractures, often replaced by ‘spaced cleavage’.

• Use of Different Type of Metamorphic rocks

Rock Name	नाम (नेपाली)	Uses
Slate	स्लेट	Used for roofing, flooring, and as a writing surface.
Marble	संगमरमर	Used in sculpture, architecture, and as a building material.
Schist	शिस्ट	Used in construction and as a decorative stone.
Gneiss	ग्नाइस	Used as a building material and for decorative purposes.
Quartzite	क्वार्टजाइट	Used in construction, as a decorative stone, and for making glass.
Phyllite	फिलाइट	Used in construction and as a decorative stone.
Amphibolite	एम्फिबोलाइट	Used in construction and as a decorative stone.

5. Structural Geology

• Introduction

The Earth’s crust is constantly subjected to forces that distort the rocks within a region. These forces can arise from the weight of overlying rocks, large-scale movements of materials, and gravity. Depending on the magnitude and duration of these forces, rocks may undergo temporary or permanent deformation.

• Definition of Structural Geology

Structural geology is the study of the mechanisms and types of deformation of rocks in the Earth’s crust due to stress from various geological processes. It involves understanding the three-dimensional distribution of rock units and their deformation histories. The primary goal is to use present-day rock geometry to infer the history of rock deformation. This field is crucial for assessing the stability of engineering structures like dams, tunnels, and bridges.

• Rock Deformations & Reasons

Rock Deformations: Rock deformations occur due to various geological processes such as tectonic activities, earthquakes, and volcanism. These processes cause stress that displaces and distorts rocks.

• The study of rock deformations focuses on:

1. Analysis of stress
2. Analysis of deformations
3. Response of rocks to stress

• Types of Strain

1. Dilation: Change in volume of rock mass.
2. Distortion: Change in volume and form of rock mass.

• Reasons for Rock Deformations

1. Stress: Defined as force per unit area, stress is a primary factor in rock deformation. It results from plate tectonics, earthquakes, volcanic actions, and other geological processes.
2. Temperature Changes
3. Wetting and Drying

• Types of Stress

1. Compressive Stress: Acts towards a common point, causing rocks to squeeze and shorten, leading to faulting and folding. Seen along convergent plate boundaries.
2. Tensile Stress: Acts away from a common point, causing rocks to elongate and stretch, leading to tensional faults and thinning. Seen along divergent plate boundaries.
3. Shear Stress: Acts tangentially along opposite surfaces, causing rocks to repel and push in opposite directions. Seen along transform plate boundaries.

• Stages of Deformation

1. Elastic Deformation

 

1. Rocks return to their original shape after the stress is removed.
2. If stress exceeds the elastic limit, plastic deformation occurs.
3. Brittle Deformation
4. Rocks rupture when stress is applied.
5. Results in geological structures like joints and faults.

• Common in brittle rocks like granite.

3. Ductile Deformation
4. Rocks undergo significant plastic deformation before rupturing.
5. Results in geological structures like folds.

• Common in rocks like rock salt.
• Attitude of Geological Structures: Dip, Strike, Trend, Plunge

1. Beds and Bedding

Beds: Layers of sedimentary rocks with planar top and bottom surfaces.

Bedding: Planar surfaces of beds, often planes of weakness.

1. Foliation

Planes of separation of mineral layers in metamorphic rocks.

1. Attitude Descriptions

Strike: The direction of the line formed by the intersection of a bedding plane with a horizontal plane.

Dip: The angle between the bedding plane and the horizontal plane, measured in two components:

Dip Direction: The direction towards which the beds are inclined.

Dip Amount: The acute angle between the bedding plane and the horizontal plane.

• Classification of Dips

1. True Dip: Perpendicular to the strike, showing the direction of maximum inclination.
2. Apparent Dip: Any dip not perpendicular to the strike.

• Relationship Between True Dip and Apparent Dip

The relationship can be expressed as:

• Dip Direction and Dip Amount: In engineering, these are crucial for slope stability analysis. If the dip direction is known, the strike can be calculated as it is perpendicular to the dip direction. However, if only the strike is known, the dip direction could be either +90° or -90° from the strike.
• Plunge and Trend

Plunge: The vertical angle between an inclined linear feature and an imaginary horizontal plane.

Trend: The compass direction in which a linear geological feature plunges. Trend and dip direction are similar but used for different features.

• Measurement of Geological Strata Orientations

Attitude Determination: Refers to the strike, dip, and dip direction of a rock bed.

Strike Line: Joins two points of equal elevation on a bedding plane.

Dip Direction: Determined by drawing a line perpendicular to the strike line, from higher to lower elevation.

• Dip Amount Calculation:

Measure the horizontal distance (XY) between two strike lines.

Calculate the dip angle using the formula:

 

 

 

• Geological Structures

1. Primary Sedimentary Structures: Formed during the deposition of sedimentary rocks.

Examples: Bedding planes, lamination, cross-bedding, graded bedding, ripple marks, mud cracks.

2. Secondary (Deformation) Structures: Formed after deposition due to deformation.
3. Continuous Structures: Formed by ductile deformation (e.g., lineation, foliation).
4. Discontinuous Structures: Formed by brittle deformation (e.g., faults, joints).

• Types of Lineation

1. Intersection Lineation: Formed by the intersection of two foliation planes.
2. Crenulation Lineation: Formed by the intersection of fold hinges and foliation.
3. Mineral Lineation: Defined by the alignment of mineral grains.
4. Stretching Lineation: Formed by the stretching of rocks during deformation.

• Types of Foliation

1. Primary Foliation: Formed during the deposition of sediments or formation of magmatic rocks.
2. Secondary Foliation: Formed by lithification and/or crystallization of rocks due to stress and strain.

• Cleavage and Schistosity:

Cleavage: A type of foliation in low-grade metamorphic rocks where the rock splits along closely spaced planes.

Schistosity: A type of foliation in medium to high-grade metamorphic rocks where platy minerals are aligned.

• Crenulation Cleavage

Formation: Occurs when an early planar fabric is overprinted by a later planar fabric.

Appearance: Seen in metamorphic rocks like phyllite, schist, and some gneiss.

• Boundinage

Formation: When a rigid tabular body of competent rock is stretched and deformed, breaking into segments called boudins.

Appearance: Typically found in shear zones, appearing sausage or barrel-shaped.

• Discontinuous Structures

Structures with cracks and breakages in the rock strata, formed by brittle and ductile deformations.

Types:

1. Faults
2. Folds
3. Joints
4. Fractures
5. Cracks
6. Faults

A fracture in rocks along which there has been relative displacement.

Formation: Result of brittle deformation due to tensional or compressive forces.

Types:

1. Normal Fault: Hanging wall moves down relative to the footwall.
2. Reverse Fault: Hanging wall moves up relative to the footwall.
3. Strike-Slip Fault: Displacement occurs parallel to the strike of the fault.
   • Fault Terminology

 

Term	Description
Fault Plane	The plane along which relative movement occurs.
Fault Line	Intersection of the fault plane with the ground surface.
Hanging Wall	The block of rock that lies above the fault plane.
Foot Wall	The block of rock that lies below the fault plane.
Displacement	Net distance between the surfaces of the blocks.
Slip	The displacement that occurs during faulting.
Throw	Total vertical displacement.
Heave	Total horizontal displacement.

• Types of Faults

1. Genetic Classification:

Normal Fault: Formed due to tensile forces.

Reverse Fault: Formed due to compressive forces.

Strike-Slip Fault: Horizontal movement due to seismic activity.

1. Geometrical Classification:

Strike Fault: Fault strike is parallel to the bedding strike.

Dip Fault: Fault strike is parallel to the bedding dip.

Oblique Fault: Fault strike makes an oblique angle with the bedding strike.

• Causes of Faulting:

1. Shearing Stresses: Cause sliding action.
2. Earth Shrinkage: Induces stress.
3. Convection Currents: Heat from the Earth’s interior.
4. Radioactive Decay: Causes dragging and compressive effects.
5. Folding of Rock Strata: Leads to faulting.
6. Brittle Nature of Rock: Makes it susceptible to faulting.
   • Types of Faults:

Normal Fault	Hanging wall moves down relative to the footwall.
Reverse Fault	Hanging wall moves up relative to the footwall.
Strike-Slip Fault	Horizontal movement along the strike of the fault.

2. Folds

Deformational structures formed due to compressional forces, resulting in bending without fracturing.

• Components of a Fold:

1. Axial Plane: Imaginary plane dividing the fold symmetrically.
2. Hinge Line: Line through the points of maximum curvature.
3. Limbs: Sides of the fold.
   • Types of Folds:

Fold Type	Description
Anticline	Convex upward, older rocks at core
Syncline	Concave upward, younger rocks at core

• Classification Based on Axial Plane and Limbs:

Fold Type	Description
Symmetrical	Limbs are mirror images, axial plane vertical
Asymmetrical	Limbs are not mirror images, axial plane inclined
Overturned	Both limbs dip in the same direction

• Other Fold Types:

 

Isoclinal Fold	Parallel axial planes, limbs dip at equal angles.
Plunging Fold	Hinge line is inclined.
Non-Plunging Fold	Hinge line is horizontal.

3. Joints

Fractures with no relative displacement along the fracture plane.

• Characteristics:

1. Result from brittle deformation due to tensile or shearing stresses.
2. Can be vertical, horizontal, or inclined.
3. Divide rock into blocks that move perpendicular to the fracture plane.
4. Differences from Faults:
5. Joints exhibit no measurable lateral movement.
6. Can be open or filled.

• Terminologies of Joints

Master Joint	A prominent, continuous joint.
Joint Sets	A group of joints occurring in the same orientation.
Conjugate Joints	Two sets of joints that are perpendicular to each other.
Joint System	A combination of two or more sets of joints representing the whole assemblage of joints in the exposure.
Open Joint	Joints where the blocks have separated or opened up slightly perpendicular to the fracture plane.
Close Joint	Joints where the blocks have no separation.
Continuous Joint	Joints that run a significant distance.
Discontinuous Joint	Joints that disappear at shorter depths or distances.
Attitude of Joint	Similar to other planar features such as bedding and foliation.

• Types of Joints

1. Geometrical Classification (Based on the attitude of joints with respect to bedding)

Dip Joint: The strike of the joint is parallel to the dip of the bedding.

Strike Joint: The strike of the joint is parallel to the strike of the bedding.

Oblique Joint: The strike of the joint makes an oblique angle with the strike of the bedding.

2. Genetic Classification

Mural Joints: Occur in massive igneous rocks, forming cubical blocks due to three sets of perpendicular joints.

Columnar Joints: Found in volcanic igneous rocks like basalt, forming hexagonal prismatic columns.

Sheet Joints: Found in massive igneous rocks, appearing as sedimentary strata.

Tension Joints: Developed due to tensile forces, common in folded sequences and igneous rocks.

Compression Joints: Developed due to compressive forces, found mainly in the core regions of folds.

Shear Joints: Developed due to shearing forces, found near fault planes and shear zones.

Spatial Relationship Basis

Regular Joints: Occur in parallel or sub-parallel sets, repeated at regular intervals (e.g., columnar joints, mural joints).

Irregular Joints: Occur randomly, without regularity in occurrence and distribution, often with curved and rough surfaces.

• Causes of Joints

1. Tensional or compressional forces acting on rock blocks.
2. Rise of pore fluid pressure beneath the Earth’s surface.
3. Shrinkage of rock strata due to cooling at low temperatures.

• Unconformities

1. Conformity: Continuous formation of rock beds without major breaks.
2. Unconformity: A depositional gap or break between two conformable sequences, representing a significant break in the geologic record.

• Types of Unconformities

Parallel Unconformity (Disconformity): Bedding above and below the unconformity surface are parallel.

Angular Unconformity: Bedding beneath the unconformity surface is folded or tilted, creating an angular relationship with the younger rocks above.

Non-Conformity: Exists between older plutonic rocks and younger sedimentary rocks.

• Field Identification of Geological Structures

1. Fold Identification

Direct Observation: Bedding of rock strata can be observed in mountain cliffs, quarries, deep cuttings, and trenches.

Repetition of Strata: Repetition of strata in a cyclic order indicates the presence of folds.

2. Fault Identification
3. Direct Evidence:

Slicken Sides: Parallel grooves formed due to frictional sliding.

Breccia: Angular, unconsolidated rock fragments found on either side of a fault plane.

Gouge: Fine-grained, unconsolidated material indicating a stressed zone.

Abrupt Termination: Sudden end of geological structures, such as dykes, indicating faults.

1. Indirect Evidence:

Repetition & Omission of Strata: Indicates the presence of faults when strata are repeated or omitted in geological mapping.

• Physiographic Features

Different types of physiographic features reflect the presence of faulting. One such feature is sudden topographic variation, where there is a sudden drop in topography due to a fault, although the fault may not be visible on the surface due to overlying sediments.

Example:

Mineralization: High stresses in faults result in intense pressure and temperature, leading to the formation of high P/T minerals like kyanite and sillimanite, commonly seen along the MCT zone. Garnet in the schist of Raduwa is another example.

• Unconformity Identification

1. Lack of parallelism of beds on opposite sides of the contact.
2. The lowest beds above the surface consist of conglomerates with pebbles of underlying formations.
3. Sharp contrast in color between rocks.
4. Intrusive contact.

• Engineering Significances of Geological Structures

1. Folds: Special considerations must be taken during construction on folded masses due to their high strain zones:
2. Dams: The flank dipping towards downstream is unfavorable, while the one dipping upstream is safer.
3. Tunneling: In synclines, stress is exerted more on the sides than on the crown. In anticlines, tensional fractures may develop on the crown, causing overbreak.

• Groundwater: Synclinal aquifers have higher groundwater potential, while anticlinal conditions are less favorable.

1. Rupture Risk: Folded areas may rupture due to further stress.
2. Faults: Faulted areas are generally unsafe and unstable for civil engineering foundations due to various hazardous effects:
3. Fractures: Faults cause considerable rock fractures, making the ground weak and unfit for foundations.
4. Groundwater: Fractures act as channels for groundwater, causing problems in tunnels and reservoirs.

• Earthquakes: Faults are often accompanied by earthquakes, which can cause severe shaking and collapse of infrastructures.

1. Landslides: If the dip direction of the fault plane and surface slope are the same, landslides may occur.
2. Recurrence: Fault planes may recur at the same place, making the ground unstable.
3. Joints: Joints are considered sources of weakness in rocks, less harmful than faults but more harmful than bedding:
4. Strength Reduction: Joints reduce the strength of rocks, especially when saturated with water, causing decay and weathering.
5. Tunneling: Intensively jointed rocks can cause overbreak and roof collapse in tunnels.

• Leakage: Joints can cause leakage problems in reservoirs and groundwater issues in tunnels.

1. Landslides: Similar to faults, the same dipping of joint planes and surface slope can cause landslides and slope failures.
2. Physical Geology

• Introduction

Physical geology is the branch of geology that deals with the Earth’s composition and the physical changes occurring on it. It involves the study of rocks, minerals, and sediments, their structures and formations, and their processes of origin and alteration.

• Different Geological Agents

The geological agents responsible for changes on Earth’s surface include running water, glaciers, groundwater, wind, and sea water. These topics will be discussed in the next chapter.

• Geomorphological Processes: Weathering & Erosion

Weathering: Weathering is the mechanical and chemical decomposition of preexisting rocks into fragments, making minerals separable and movable due to atmospheric conditions. It involves two main processes: mechanical and chemical weathering.

Mechanical Weathering: Breaks down rocks without changing their chemical nature. Examples include freezing and thawing of water, pressure release, salt crystal formation, plant root growth, and physical effects of water, ice, wind, and temperature changes.

Chemical Weathering: Involves chemical changes to minerals that become unstable when exposed to surface conditions. It is most effective in warm, wet climates.

• Types of Weathering

Mechanical Weathering: Physical forces break down rocks without changing their chemical composition.

Chemical Weathering: Atmospheric or biologically prepared chemicals cause chemical changes in minerals.

• Erosion

Erosion is the process of weathering and transporting solids (sediment, soil, rock, and other particles) from their source to other locations. The main agents of erosion are wind and running water, with minor agents including glaciers, ice, and gravity.

• Geological Cycle

The geological cycle involves the continuous process where hot molten materials form igneous rocks, which are then broken down by weathering to create soil and sedimentary rocks. This cycle includes the hydrologic cycle, rock cycle, and tectonic cycle.

• Geological Agents

1. Running Water

Running water, such as streams and rivers, moves from high to low gradients, carrying and depositing materials along the way. River channel morphology refers to the channel pattern and geometry at various points along a river.

2. Straight Rivers: Follow a straight path, typically found in steep topography with high flow velocity and high erosion rates.
3. Meandering Rivers: Follow a zigzag path, found in areas with moderate relief and gradient, with balanced erosion and deposition rates.
4. Braided Rivers: Have multiple paths that may converge, found in low-gradient areas with high sediment deposition rates.

• Features Developed by Rivers

Feature	Description
V-shaped Valley	Formed by river erosion confined to downward cutting.
Gorges/Canyons	Deep, narrow valleys with steep walls, e.g., Grand Canyon of Colorado River.
River Terraces	Flat surfaces along river valleys formed by episodic river down-cutting.

• Glaciers

Glaciers are large, thickened ice masses formed from compressed snow over many years. They flow constantly under their own weight due to gravity.

• Depositional Features

1. Till: A heterogeneous mixture of materials picked up by the glacier, ranging from tiny clay particles to large boulders.
2. Moraines: Rounded deposits of glacial till formed through various processes.
3. Outwash Plains: Alluvial plains composed of glacially eroded and sorted sediments transported by meltwater streams.
4. Kettle Holes: Depressions formed on outwash plains or till after isolated ice blocks melt.
5. Drumlins: Smooth, elliptical hills made of till, lying parallel to the movement of ice.
6. Kame: Short ridges or mounds of sand and gravel deposited during glacial melting.
7. Buried Valleys: Deep valleys excavated by glacial erosion and filled with glacial deposits.

• Erosional Features

1. Striations: Gouges or scratches in bedrock caused by glacier movement.
2. U-shaped Valleys: Valleys with steep sides and flat floors formed by glacial scouring.
3. Hanging Valleys: Smaller valleys formed by differential erosion rates, often featuring waterfalls.
4. Cirques: Bowl-shaped basins formed by glaciation, often containing small lakes (tarns).
5. Horns: Sharp-edged peaks formed by the erosion of three or more arêtes.
6. Fiords: U-shaped valleys filled with ocean water.
7. Arêtes: Narrow ridges separating adjacent valleys or cirques.

• Ground Water

Groundwater is water present beneath Earth’s surface in soil pore spaces and rock fractures. It is less vulnerable to pollution than surface water.

• Features Produced by Ground Water

Depositional Features

1. Geodes: Spherical rock structures with mineral-lined cavities.
2. Stalactites: Formations hanging from cave ceilings formed by mineral deposits from dripping water.
3. Stalagmites: Formations rising from cave floors formed by mineral deposits from dripping water.
4. Replacement Deposits: Mineral deposits formed by chemical processes replacing original rock.

Erosional Features

1. Sinkholes: Funnel-shaped cavities formed by the solvent action of groundwater on carbonate rocks.
2. Caverns: Tunnels and underground chambers formed by groundwater dissolution of limestone.
3. Solution Valleys: Enlarged valleys formed by the continuous solution of limestone.
4. Karst Topography: Landscapes formed from the dissolution of soluble rocks, characterized by sinkholes and caves.
5. Stylolites: Interlocked, tooth-like columns of stone formed by pressure dissolution.

• Wind

Wind is the movement of air caused by the uneven heating of the Earth by the sun. It can shape landforms through various processes.

• Features Produced by Wind

Depositional Features

1. Sand Dunes: Accumulations of sand grains shaped into ridges by wind.
2. Loess: Deposits of silt or materials brought by wind, forming fertile topsoil.
3. Sand Sheets: Large, flat areas of sand where grain size is too large or wind velocity too low for dune formation.

Types of Sand Dunes

1. Transverse Dunes: Elongated dunes with their longer axis at right angles to the wind direction.
2. Longitudinal Dunes: Dunes with rounded or pointed tops, elongated in the wind direction.
3. Barchan Dunes: Crescent-shaped dunes with the convex side facing the wind direction.

• Sea Water

Sea Water makes up the oceans and seas, covering more than 70% of Earth’s surface. It is a complex mixture of 96.5% water, 2.5% salt, and smaller amounts of other substances.

• Features Produced by Sea Water

Depositional Features

Feature	Description
Bench	Flat masses of sand and gravel deposited along sea shores.
Spits	Stretches of sand extending from the mainland into the sea.
Sand Bars	Partly exposed ridges of sand or coarse sediment built by waves offshore from a beach.
Tombolo	A landform where an island is attached to the mainland by a narrow piece of land such as a spit or bar.
Abyssal Plains	Flat areas on the ocean floor between the continental rise and mid-ocean ridges or trenches.
Coral Reefs	Erosion-resistant mounds composed of coral skeletons.
Atolls	Ring-shaped coral reefs or strings of closely spaced small coral islands, enclosing or nearly enclosing a shallow lagoon.

Erosional Features

Feature	Description
Wave-cut Cliffs	Narrow flat areas at the base of sea cliffs or along shorelines created by the weathering of land.
Wave-cut Benches	Flat, bench-like sections of cliffed coast lying above the wave-cut or shore platform.
Bays	Coastal bodies of water that directly connect to a larger main body of water such as oceans, lakes, or other bays.

• Volcanism

A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Earth’s volcanoes occur because its crust is broken into 17 major rigid tectonic plates. Volcanism is the phenomenon of eruption of molten rock (magma) onto the surface of Earth through a vent. It includes all the phenomena that cause magma to rise through the crust and form volcanic rocks on the surface.

• Types of Volcano

Type	Description
Active Volcano	A volcano that has had at least one eruption during the past 10,000 years.
Dormant Volcano	An active volcano that is not currently erupting but is expected to erupt again.
Extinct Volcano	A volcano that has not erupted for at least 10,000 years and is not expected to erupt again.

• Volcanic Products

Three types of materials are ejected during a volcanic eruption:

1. Gaseous Products:
2. About 90% of the total gas content is steam.
3. Other gases include carbon dioxide, nitrogen, sulfur dioxide, hydrogen, and carbon monoxide.
4. Liquid Products:

Lava is the liquid product of a volcano.

3. Solid Products:

Enormous quantities of solid products are ejected, consisting of fragments of rocks or pieces of already cooled lava.

• Classified by size and shape:

1. Volcanic Blocks: Largest masses of rock, usually angular, with diameters above 32 mm.
2. Volcanic Bombs: Rounded or spindle-shaped masses of hardened lava, often with twisted ends indicating rapid rotation in the air.
3. Cinders or Lapilli: Fragments between 4 mm and 32 mm in size.
4. Ash: Fine particles of lava ranging in size from 0.25 mm to 4 mm.
5. GEOLOGY OF NEPAL

• Introduction To The Physiography & Tectonic Division Of Nepal Himalaya

Prior to 40 million years ago, there was a sea called Tethys between the Indian subcontinent and the Tibetan plateau. The Indian subcontinent gradually moved towards the Tibetan plate, and around 40 million years ago, they came into contact, causing the Tethys Sea to disappear. The Indian continental crust, being lighter, could not sink into the mantle and remained beneath the Tibetan continental crust.

The Himalayas were formed about 2 million years ago due to the collision of rock masses from the north and south and are still rising at a rate of 2-5 mm per year. The Himalayan range extends about 2400 km from the Indus Valley in the west to Assam in the east. The collision caused the northern margin of the Indian continent to shorten and slice into three principal thrusts: the Main Central Thrust (MCT), the Main Boundary Thrust (MBT), and the Main Frontal Thrust (MFT).

• Based on these faults and thrusts, nepal himalaya can be divided into five major tectonic zones:

1. Terai Zone
2. Siwalik Zone
3. Lesser Himalaya Zone
4. Higher Himalaya Zone
5. Tibetan Tethys Zone

• Major Discontinuities System of Nepal Himalaya

1. Himalaya/Main Frontal Thrust (Hft/Mft)
2. Located at the boundary of the Siwalik and Terai.
3. Considered active with a maximum earthquake potential of magnitude 6.5.
4. North dipping fault.
5. Main Boundary Thrust (MBT)
6. Located at the boundary of Lesser Himalayas and Siwalik.
7. Considered active with earthquakes up to magnitude 8.
8. Steep north dipping fault.
9. Main Central Thrust (MCT)
10. Located at the boundary of Higher Himalaya and Lesser Himalaya.
11. Less active now but was active during early phases of Himalaya formation.
12. Earthquakes up to magnitude 7.5.
13. North dipping fault.

• Engineering Significances of Discontinuities

1. Thrust zones are prone to landslides, rock falls, debris flows, and mudflows.
2. Thrusts influence the movement of surface water and can cause sudden changes in river courses, affecting underground water.
3. Thrust zones are porous, weak, unstable, and incompetent, raising concerns about the stability of engineering structures.
4. Active thrusts near engineering sites are vulnerable to earthquakes and should be avoided for heavy construction.

• Geology of Terai Zone

1. The southernmost tectonic division of Nepal, part of the northern end of the Gangetic plain.
2. Bounded by the Himalayan/Main Frontal Thrust (HFT/MFT) in the north.
3. Width varies from 10 to 50 km from east to west.

Divided into three regions:

1. Northern (Bhabar) Region: Composed of thick beds of pebbles and boulders, acts as a recharge zone for groundwater.
2. Middle (Marshy) Region: Flat, marshy land with gravel beds, sand horizons, and clay layers.
3. Southern Region: Composed of finer sediments like clays, silts, and fine sands.

• Geology of Siwalik or Churia

1. Represents the lower hills of the Churia range.
2. Bounded by MBT to the north and MFT to the south.
3. Covered with thick forests and composed of young sedimentary rocks.
4. Rocks dip northwards with an overall east-west strike.

Divided into three parts:

1. Lower Siwalik: Fine-grained sandstone, mudstone, siltstone, and shale.
2. Middle Siwalik: Medium-grained, thick sandstones with biotite, quartz, and feldspar.
3. Upper Siwalik: Very coarse-grained rocks such as boulders and conglomerates.

• Geology of Lesser Himalaya Zone

1. Bordered by MBT to the south and MCT to the north.
2. Width: 60-80 km.
3. Composed mostly of unfossiliferous metasedimentary and metamorphic rocks like shale, sandstone, limestone, dolomite, slate, phyllite, schist, marble, and quartzite.
4. Highly faulted and folded, with complex structures.
5. Contains magmatic intrusions like granite and pegmatite.

Divided into three physiographic units:

1. Mahabharat
2. Midland
3. Frontal

• Geology of Higher Himalaya

1. Bordered by MCT to the south and STDs to the north.
2. Contains the highest peaks in the world, including many above 8000 m.
3. Rugged terrain with steep slopes and deep valleys.
4. Receives heavy precipitation (2000 mm to 5000 mm).
5. Composed of high-grade metamorphic rocks like gneisses, marbles, schist, and quartzite, with high-grade index minerals like kyanite and garnet.
6. Contains high snow-clad mountains and granite intrusions.

• Geology of Tibetan Tethys Zone

1. Bordered by STDs in the south and the Tibetan Tethys zone in the north.
2. Composed of sedimentary rocks such as shale, limestone, and sandstones.
3. Fossiliferous rocks well developed in Thak Khola, Manang, Mustang, and Dolpa.
4. Covered with thick, loose, fragile, glacial, fluvial-glacial deposits along with recent alluvium.
5. Physiographic and Geological Divisions of Nepal

Physiographic Unit	Geological Unit	Geological Structure
Terai	Terai	HFT
Churia Range	Siwalik	MBT
Dun Valleys	Siwalik	MBT
Mahabharat Range	Lesser Himalaya	MBT
Midland	Lesser Himalaya	MBT
Fore Himalaya	Lesser Himalaya	MBT
Higher Himalaya	Higher Himalaya	MCT
Tibetan Tethys Zone	Tibetan Tethys	STDs

• Study of Geological Units: Complex, Group, Formation & Member

The sequence of rocks is subdivided based on their lithology. From smaller to larger scale, the main units recognized are member, formation, group, and complex/super group. They are described as follows:

Formation:

A series of beds distinct from other beds above and below, thick enough to be shown on geological maps.Boundaries between formations are not necessarily sharp.

Group:

1. A series of formations classified together to define a group.
2. Can be a few thousand meters thick and represent rocks deposited within a single basin.
3. May consist of different formations in different geographical areas, and individual formations may appear in more than one group.

Members:

1. In areas where detailed geological information is needed (e.g., mining or petroleum districts), a formation might be divided into members, each with a specific and distinct lithology.
2. For example, a formation that includes both shale and sandstone might be divided into members, each of which is either shale or limestone.