Earth Science: Weathering of Rocks PDF

**LEARNING ACTIVITY SHEET** QUARTER II/ SEMESTER I **Name**:\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ **Score**:\_\_\_\_\_\_\_ **Grade & Section** \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_**Subject**: **EARTH SCIENCE** **Name of Teach...

**LEARNING ACTIVITY SHEET** QUARTER II/ SEMESTER I **Name**:\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ **Score**:\_\_\_\_\_\_\_ **Grade & Section** \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_**Subject**: **EARTH SCIENCE** **Name of Teacher**: **Date**: \_\_\_\_\_\_\_\_\_\_\_\_\_ I. **Title:** **Weathering of Rocks** II. **Type of Activity:** Concept notes with formative activities III. **MELCs:** Describe how rocks undergo weathering **(S11ES-IIa-22)** IV. **Learning Objective/s:** Determine the types of weathering and causes **V. Reference/s** For Print Material/s: Olivar III, J. T. Rodolfo, R. S. & Cabria, H. Exploring Life Through Science Series-Earth Science, pp. 105-119. Religioso, T. F.& Vengco, L. G., Discovering Earth and Solar System, pp. 116-124. Thompson, G. R. & Turk, J., Introduction to Earth Science, pp. 207-213 For Online Resource/s: Soil Management: Soil for life.. Retrieved at on August 26, 2020 **Concept notes with formative activities** Weathering: On-site breakdown of rock and its eventual transformation into sediments. They accumulate where they form. However, loose soil and weathered materials are easily carried by wind and rain. (A famous view in Kapurpurawan Rock Formation, Burgos, Ilocos Norte, which shows weathering through wind) Weathering occurs by both mechanical and chemical processes. Mechanical Weathering: Physical breakdown of rock into unconnected grains or chunks without altering its chemical composition. They are not different with their parent rock except they are smaller. - Frost Wedging (Temperate Regions) - Water accumulates in a crack and then freezes, the ice expands and wedges the rock apart. In some temperate countries who during spring and fall, the rate of frost wedging maybe fast. ice forms at night and melts the next morning. So mountaineers try to hike by early morning before ice melts. A pile of loose angular rock debris from frost wedging is called talus **Abrasion** Rocks, grains of sand, and silt collide with one another when currents or waves carry them along a stream or beach. During these collisions, their sharp edges and corners wear away and the particles become rounded. It is a mechanical wearing of rocks by friction and impact. - Root wedging - Salt wedging (crystallization of salt) - Thermal Expansion **Chemical Weathering** Occurs when there are chemical changes in at least some of the components of the rock. **DISSOLUTION** Minerals dissolve readily in water but others do not. Dissolution happens when a crystal mineral dissolves in water and form a solution. NaCl (Halite) dissolves rapidly and completely in water that it is rare in moist and natural environment. to understand how water dissolves a mineral, think of an atom on the surface of a crystal. It is held in place because it is attracted to the other atoms in the crystal by electric forces called chemical bonds. At the same time the electrical attractions to the outside environment are pulling away from the crystal. The result is like a tug-of-war. If the bonds between the atom and the crystals are stronger than the attraction of the atom to its outside environment, the crystals remain intact. They pull atom away from crystal and the mineral dissolves. Rocks and minerals dissolve more rapidly when water is acidic or basic. Limestones contain calcite (CaCO3). Calcite barely dissolves in pure water but is quite soluble to acid. Carbon dioxide could be formed (seen in bubbles) when a strong acid gets attached to calcite. Raindrops is slightly acidic as atmospheric carbon dissolves. Also, air pollution could increase ph level of rainwater. Thus water (acidic or basic)- dissolves ions from soil and bedrock and carries the dissolved materials awat. Ground water also dissolves rock to produce Spectacular caverns in limestones. **HYDROLYSIS** Water reacts with one minerals, breaks them down, and form a new mineral that has water as part of its crystal structure. Feldspar, the most common rock-forming mineral, weathers through hydrolysis. When granite weathers, the feldspar and other minerals decompose to form clay but the unaltered quartz grains fall free from the rocks. Hydrolysis has so deeply weathered some granites that quartz grains can be pried out with a fingernail; at depths of several meters. The presence of sand-like granules in a weathered rock is a sign of hydrolysis weathering. Hydrolysis takes place when acid rain reacts with rock-forming minerals such as feldspar to produce clay and salts that are removed in solution.  **OXIDATION** Many elements react with atmospheric oxygen O~2~. Reaction of oxygen with mineral in the rock, form oxides. Usually happens to iron-bearing rocks. Rusting is an example of a more general weathering process. Many valuable metals such as iron, copper, lead, and zinc occur as sulfide minerals in ore deposits. When they oxidize during weathering, the sulfur reacts to form sulfuric acid, a strong acid. The sulfuric acid washes into streams and ground water. Where it may harm aquatic organisms. Many natural ore deposits generate  **Biological weathering** Occurs in roots of plants. When fungi and lichens secrete organic acids that dissolve minerals and the nutrients taken in by these organisms. **EROSION** Erosion is **the separation and removal of weathered and unweathered rocks and soil** from its substrate due to gravity or transporting agents like wind, ice or water. Agents of erosion may carry the weathered materials in great distances and finally deposit it as layers of sediment at Earth's surface. Weathering decomposes bedrock, and plants add organic material to the regolith to create soil at Earth's surface. However, soil does not accumulate and thicken throughout geologic time. If it did, Earth would be covered by a bunch of soil hundreds or thousands of meters thick, and rocks would not exist at Earth's surface. Instead, interactions with flowing water, wind, and glaciers erode soil as it forms. Some eroded materials are also influenced by gravity. All forms of erosion combine to remove soil about as fast as it forms. For this reason, soil is usually only a few thick or less in most parts of the world. As soil erodes, opens the journey of these materials to lead to streambed, a sand dune, a lakebed which are all temporary stops. Eventually, they erode again and are carried downhill and finally they are deposited where the land meets the sea. Some accumulates on deltas, and coastal marine currents redistribute some of it along the shore. Eventually, younger sediment may bury older layers until they become lithified to form sedimentary rocks. Transport is **the process by which sediments are moved along from the source** to where they are deposited Wind erosion commonly occurs in flat, bare areas, or dry, sandy and loose soils. It detaches soil particles and transports them by wind. Sandstorms could transport lots of sediments for hundreds of kilometers. This could damage the land and natural vegetation by removing soil from one place and depositing it in another area such as farmland or built-up areas. It results to soil loss, dryness, and deterioration of soil structure, soil nutrient productivity losses and air pollution. Paoay and Laoag sand dunes are formed through this process. Glaciers shows evidence of movement due to gravity. Glaciers have enormous erosive power. As rocks move over a rock, it acts like a bulldozer; the rocks at the surface are scraped-off and grinded against the mixture of ice and rocks. It moves slowly but erodes downward rapidly, forming U-shaped valleys. This erosion process is dominant in Polar Regions and in high altitude mountains. Water IS THE MOST COMMON AGENT of erosion. Millions of tons of sediment is picked-up and transported everyday along rivers, coasts and in deep oceans around the world. Sediments move along in four ways: Traction: **Rolling or Dragging** of large grains aided by push or large drains Saltation: Bouncing of sand grains as they are picked-up, carried along and dropped repeatedly Suspension: Movement of fine particles like silt and clay Solution: Movement of soluble minerals (salts)  Before rivers are tributaries (V-shaped) found in elevated areas as mountain which is characterized to have strong erosive power. While in gentler and wider valleys (U shaped), the sediments transported get smaller and smoother. For lowlands, rivers form meanders and form very wide floodplains  As river enters the sea, it separates into branches called distributary channels It deposits most of its sediments forming TIDAL FLATS  Coastal Erosion is primarily caused by wave action forming cliffs and arches TIDAL CURRENT can also move sediments towards the ocean **MASS WASTING** Downslope movement of rocks, soil, or any earth material, primarily due to gravity. The word landslide is a general term of mass wasting and for thee landforms created by mass wasting. Although gravity acts constantly on all slopes, the strength of rock and soil usually hold the slope in place. In some places, however, natural processes or human activity may destabilize a slope and cause mass wasting. For example, a stream can erode the base of a hillside, undercutting it until it slides. Rain, melting snow, or a leaking irrigation ditch can add weight and lubricate soil, causing it to slide downslope. Mass wasting occurs naturally in a hilly or mountainous terrain. Steep slopes are especially vulnerable, and landslides scars are common in the mountains. **Controlling factors in mass wasting** **a. Slope Angle:** A cardboard and an eraser above it, what happens to the erase if we increase the tilt of the board? Components: 1\. Component of gravity perpendicular to the slope which helps hold the object in place 2\. Component of gravity parallel to the slope which causes shear stress and helps move objects downslope As the slope increase, the slope-parallel component increases while the slope perpendicular component decreases. Thus the tendency to slide down the slope becomes greater. All forces resisting movement downslope can be grouped under the term shear strength. This is controlled by frictional resistance and cohesion of particles in an object, amount of pore pressure of water, and anchoring effect of plant roots. When shear stress \> shear strength, downslope movement occurs **b. Role of water.** 1\. Water has the ability to change the angle of repose (the steepest slope at which a pile of unconsolidated grains remain stable). To demonstrate this concept, you can build a sand hill using dry, damp, and water-saturated sand by flipping a paper cup full of the sand material upside down on a paper plate. Note that dry, unconsolidated grains will form a pile with slope angle determined by its angle of repose. For slightly wet sand, a high angle of repose will be observed while a very low angle of repose will be observed for water-saturated sand. Why is this so.? This is due to surface tension that holds the grains together and helps them stick more than they do when they are dry. The opposite happens for sand with too much water. In saturated sand, all the pore spaces are filled with water eliminating grain to grain contact. Water in the interconnected pores exerts pressure which then reduces the shearing force between the particles. Thus the angle of repose is also reduced. 2\. Addition of water from rainfall or snowmelt adds weight to the slope. 3\. Water can reduce the friction along a sliding surface **c. Presence of clays.** 1\. Expansive and hydrocompacting soils -- contain a high proportion of smectite or montmorillonite which expand when wet and shrink when they dry out, 2\. Sensitive soils -- clays in some soils rearrange themselves after dissolution of salts in the pore spaces. Clay minerals line up with one another and the pore space is reduced. 3\. Quick clays -- water-saturated clays that spontaneously liquefy when disturbed d\. Weak materials and structures -- become slippage surfaces if weight is added or support is removed (bedding planes, weak layers, joints and fractures, foliation planes). **Classifying mass wasting processes.** A. Slope failures- sudden failure of the slope resulting in transport of debris downhill by rolling, sliding, and slumping. 1\. Slump -- type of slide wherein downward rotation of rock or regolith occurs along a curved surface. 2\. Rock fall and debris fall-- free falling of dislodged bodies of rocks or a mixture of rock, regolith, and soil in the case of debris fall 3\. Rock slide and debris slide- involves the rapid displacement of masses of rock or debris along an inclined surface B. Sediment flow- materials flow downhill mixed with water or air; Slurry and granular flows are further subdivided based on velocity at which flow occurs 1\. Slurry flow -- water-saturated flow which contains 20-40% water; above 40% water content, slurry flows grade into streams Solifluction -- common wherever water cannot escape from the saturated surface layer by infiltrating to deeper levels; creates distinctive features: lobes and sheets of debris Debris flow -- results from heavy rains causing soil and regolith to be saturated with water; commonly have a tongue-like front; Debris flows composed mostly of volcanic materials on the flanks of volcanoes are called lahars. Rodolfo, K.S. (2000) in his paper "The hazard from lahars and jokulhaups" explained the distinction between debris flow, hyperconcentrated flow and mudflow: debris flow contains 10-25 wt% water, hyperconcentrated stream flow has 25-40 wt% water, and mudflow is restricted to flows composed dominantly of mud Mud flow -- highly fluid, high velocity mixture of sediment and water; can start as a muddy stream that becomes a moving dam of mud and rubble; differs with debris flow in that fine-grained material is predominant; 2\. Granular flow - contains low amounts of water, 0-20% water; fluid-like behavior is possible by mixing with air  Creep -- slowest type of mass wasting requiring several years of gradual movement to have a pronounced effect on the slope ; evidence often seen in bent trees, offset in roads and fences, inclined utility poles. Creep occurs when regolith alternately expands and contracts in response to freezing and thawing, wetting and drying, or warming and cooling. Earth flow -- involves fine-grained material such as clay and silt and usually associated with heavy rains or snowmelt; tend to be narrow tongue-like features that that begin at a scarp or cliff Grain flow -- forms in dry or nearly dry granular sediment with air filling the pore spaces such as sand flowing down the dune face Debris avalanche -- very high velocity flows involving huge masses of falling rocks and debris that break up and pulverize on impact; often occurs in very steep mountain ranges. Some studies suggest that high velocities result from air trapped under the rock mass creating a cushion of air that reduces friction **events that trigger mass wasting processes.** a\. Shocks and vibrations -- earthquakes and minor shocks such as those produced by heavy trucks on the road, man-made explosions b\. Slope modification -- creating artificially steep slope so it is no longer at the angle of repose c\. Undercutting -- due to streams eroding banks or surf action undercutting a slope d\. Changes in hydrologic characteristics -- heavy rains lead to water-saturated regolith increasing its weight, reducing grain to grain contact and angle of repose; e\. Changes in slope strength -- weathering weakens the rock and leads to slope failure; vegetation holds soil in place and slows the influx of water; tree roots strengthen slope by holding the ground together f\. Volcanic eruptions - produce shocks; may produce large volumes of water from melting of glaciers during eruption, resulting to mudflows and debris flows