Geol Part 1.docx

SEDIMENTARY ROCKS

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Sedimentary Processes 1. 2. 3. 4. 5.

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Weathering Erosion Transport Deposition Diagenesis

Types of Chemical Weathering 1.

Weathering -

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Physical breakdown (disintegration) and chemical alteration (decomposition) of rocks at or near the Earth’s surface. Product: sediments and dissolved ions Earth materials’ response to a change of environment Mechanical- accomplished by physical forces that break the rock into smaller pieces without changing the composition Chemical- chemical transformation of rock into new compounds Agents of weathering: wind, water, ice (glacier), fauna, and flora

Mineral Quartz Feldspars Amphibole

Olivine

Residual Product Quartz Clay Mineral Clay Minerals, Limonite, Hematite Limonite, Hematite

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Mat. In Sol’n Si Si, K+, Na+, Ca2+ Si, Ca2+, Mg2+

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Si, Mg2+

Weathering Types 1.

Breaks down rock and components and internal structure of minerals producing more stable constituents No change until environment’s conditions are changed (e.g. temp, pH, etc.)

Mechanical Weathering a. Frost wedging: freezing and thawing of ice due to alternating seasons b. Salt crystal growth: evaporation of saline water leaving salt c. Thermal expansion/contraction- of water normally due to alternating dry and wet season: desiccation of cracks d. Sheeting/unloading- reduction of pressure as overlying rocks are eroded away (common in plutons) e. Biological activity- burrowing animals, plants, humans Chemical Weathering

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Dissolution- solids dissolving in a liquid o NaCl -> Na+ + Clo Ca2+, Mg2+, Na, K (highly soluble in water) Hydrolysis- minerals reacting with water to form hydroxides - Feldspar -> clay and salts Acidification- H+ in water accelerates weathering o CO2 (air) + H2O -> H2CO3 (carbonic acid) o CaCO3 (limestone) + H2CO3 (carbonic acid) -> Ca(HCO3)2 (carbonic bicarbonate) Hydration- combination of a solid mineral or element with water o CaSO4 + 2H2O; Anhydrite -> Gypsum Oxidation and reduction- combination of oxygen with a compound and the change in oxidation number of some chemical element o 4FeO (ferrous oxide) + O2 -> 2Fe2O3 (ferric oxide) o 4Fe3O4 (magnetite) + O2 -> 6Fe2O3 (hematite) o 2Fe2O3 (hematite) + 3H2O -> 2Fe2O3 + H2O (limonite) O + Fe -> Fe-oxide Al + Si + O -> Clay

Rates of Weathering Differential Weathering -

difference on rates of weathering as a function of composition, climate and physical properties

Rock Characteristics -

Structures- joints and fractures Composition- Goldich stability series; fine-grained rocks more prone to weathering (competent vs. incompetent)

Climate and Relief -

Arid and high relief- less chemical weathering and shorter transport Humid and low relief- enhanced chemical weathering and longer transport

Soil and Regolith -

Regolith- layer of rock and mineral fragments produced by weathering Soil- combination of decomposed and disintegrated rock (mineral matter) and organic matter (humus), water and air; is the portion of regolith that supports plant life

Layers of the Soil -

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O horizon (organic)- loose and partly decayed organic matter A horizon (organic + minerals) mineral matter mixed with some humus (Silica, Mg, K, Na, etc.) E horizon (eluviation) - zone of eluviation and leaching B horizon (illuviation) - accumulation of clay transported from above C horizon- partially altered parent material Unweathered parent material

Controls of soil formation -

Climate and topography- type, depth, degree and rate of weathering Parent material and biological factors- rate of weathering and composition of corresponding soil

Erosion -

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Physical removal of material by gravity, mobile agents such as wind, water, ice, or fauna Traction - dragged or rolled along the bed Saltation - pick up and deposited (hopping) Suspension - carried along the water column Solution - some materials are dissolved Competence (max size) vs Capacity (max load) of an agent

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Erosion and Transportation (greater length and transportation, greater erosion) A. Sorting - Very poorly sorted - Poorly sorted - Well sorted - Very well sorted B. Angularity and Sphericity - Angular - Subangular - Subrounded - Rounded Transportation of Sediments -

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Gravity Water

Grain size- measure of the energy of the transporting agent (greater grain size, mas energetic, mas malayo, mas fine grained) Roundness- measure of angularity of the corners of the sediments; degree of transportation (mas malayo, mas bilog) Sorting- measure of uniformity of grain size within the rock; degree of transportation and energy of transporting agent (far from source, mas well sorted)

Interpretation Poorly sorted

Transport Agent Gravity and Glaciers (and Rivers) Well Sorted Water and Wind - Textural maturity- rounded, well-sorted vs. compositional maturity - quartz rich + clay minerals Erosion -

Seawalls along shorelines (Panget na idea) Vegetation along slopes (Better idea to avoid erosion)

Deposition -

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Agents of Weathering -

Wind Ice

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Wind and water currents slow down and as glacial ice melts (for materials transported as solids) -> detrital sedimentary rock aka clastic sedimentary rock When chemical or temperature changes causes precipitation (for dissolved material) -> chemical sedimentary rocks When undecayed organic materials piles up (coal)

Diagenesis -

sum of physical and chemical processes by which sediments are lithified into sedimentary rocks  Pore spaces and pore waters  Compaction: burial by succeeding sedimentation  Cementation: precipitation of the cement glue (“glue”) around clasts from pore waters  Recrystallization: unstable crystals to more stable counterparts  Replacement: dissolution of unstable to be replaced by a more stable mineral  Bioturbation: burrowing animals  *Shells - aragonite (CaCO3) to calcite (CaCO3, but different internal structure)

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Sedimentary structures Bed/Strata -

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Clasts- large sediments; matrix- finer components; and cement (precipitate “glue”) Minerals- clay minerals, quartz, micas, and feldspars indicate source rock and climate Lithic fragments and organic materialindicates source rock and degree of transportation Classified depending in grain size (+roundness +-sorting

Chemical sedimentary rocks- transported as dissolved substances -

chemical or biochemical (if precipitation is facilitated by marine animals) Clasts- large grains; and matrix (including cement)

Classified by composition -

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Limestone- if carbonates (coquina- made up of shells ex. (Carbonate) Tests (and its products are chalk) Dolostone- if Mg-rich carbonate (dolomite) Chert- if siliceous materials Evaporites -if halides and sulfates

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Graded beds- particles within a single sedimentary layer gradually change from coarse (bottom) to fine (top) Cross bedding- characteristic “bedding” type of dunes, river deltas and some stream channel (inclined)

Flame structures (can be found within the beds, sa may bedding plane) -

coarser sediments pressing down on the finer sediments causing them to start to rise, resulting to flame structures

Ripple marks -

small waves of sand that develop on the surface of a sediment layer by the action of moving water or air

Desiccation cracks -

environment of deposition experiences alternating wet and dry periods

Sole marks- depressions that gets filled with sediments because of energy flowing water telling us the idea of the current direction Flute marks- direction of current Tool marks Imbrication- alignment of pebbles

Coal -

layer of accumulated sediments separated by bedding planes; characteristic feature of sedimentary rocks Interbeds signifying an environment of alternating low and high energy: results to differential weathering

Types of Beds

Classifying sedimentary rocks Detrital sedimentary rocks- transported as solid

in anoxic environments (e.g.) stagnant swamps) when aerobic decomposition is scarce leading to undecomposed organic material Peat (partially altered plant material), Lignite (soft, brown coal), Bituminous (soft, black coal), Anthracite (Hard, black coal)

organic sedimentary rock

Bioturbation and ichnofossils- structures by organisms(bioturb) traces of life but not remains (ichno)

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Sedimentary Environments -

a geographic setting where sediments is accumulating and/or erosion occurs; Physically, chemically, and biologically distinct from adjacent terrane Differentiated using their properties:  Physical: geology, geomorphology, climate, temperature and depth (marine)  Chemical: salinity, O2 content  Biological: fauna and flora

Sedimentary Facies -

a mass of sedimentary rock which can be distinguished from others having the same age in terms of geometry, lithology, sedimentary structure, paleocurrent patter and fossil content (Selley, 1970)

How to recognize the environment 1.

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Geometry  a function of pre-depositional topography, geomorphology, and its post-depositional history  fan-shape of an alluvial fan, triangular shape of deltas Lithology  parameters easily observed and has environmental significance  grain size, sorting, shape, and texture often reflect process of the environment  sand deposits of desert environments vs. silt to clay-sized sediments of lake environments Sedimentary Structures  important indicators of sedimentary environment  cross-bedding for river (fluvial) environments Fossil Content  one of the most important tools in identifying the depositional environment  two assumptions are made: a. the fossil lived in the place where it was buried

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the habitat of the fossil can be deduced either from its morphology or from studying its living descendants (if there are any) Trace fossils (foot print) are useful: they occur in situ (cannot be reworked, some trace fossils characterize particular environment Coral fossils and bioturbation

*Water is the most important erosional agent sculpting Earth’s landscape Fluvial (River Systems) Drainage Basin (a.k.a. Watershed) -

fundamental geomorphological unit within which precipitation is transferred to the sea, lake or larger river

Stream- a water flowing through a channel; River- stream that carry substantial amounts of water and have numerous tributaries. (tributaries vs. distributaries) o o o o o o

River head- where river begins River flow- downhill Tributary- small creek or river that runs into a larger one River mouth- where river ends Mouth- empties into lake or ocean often forms a delta with extensive wetlands Sea or lake

Base level- lowest elevation to which a river can erode its channel = to the level at which the mouth of a stream enters its ultimate base level- the ocean or temporary base levels such as a lake or a trunk stream; Knickpoint- a point of sudden change in channel slope (e.g. water falls because of resistant rock type) Graded stream- has the necessary slope to maintain the minimum velocity required to transport the material Shaping stream valleys: a.

Valley deepening- when stream’s gradient is steel and channel is above base level (=rapids and waterfalls)

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Valley widening- when stream approaches graded condition, energy is directed side to side (=erosional floodplain- a broad valley of alluvium) Incised meanders and stream terraces: valley widening phase -> uplift or base lvl decreased

Two types of stream 1.

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Meandering streams- streams that move in sweeping bends on deep and smooth channels while carrying most of their load (mostly mud sized to fine gravel) as suspension *evolution from point bats and cut banks to oxbow lakes and cutofffs *sinuosity a. Flood plains- low lying areas along the sides of a river that during regular times of heavy water flow can be blooded by spill over from the river. *Yazoo tributary- dating part ng mainstream b. Natural levees- levees that parallel their channel on both banks built by eats of successive floods (Bankswamps and Yazoo tributary); Candon, Ilocos Sur; Pampanga Iber Braided Stream- streams that flow on complexly networked diverging/converging channels. Stream’s load- coarse material (sand and gravel) with a highly variable discharge. (Abra River; Ilocos Stream) a. Bars- Elongate structures where coarse sediments are deposited during periods of low discharge b. Drainage Patterns- response of the drainage system to the type of material and structures (folds, faults, and fractures) present in the area.

Types of Drainage Patterns a. b. c. d.

Dendritic pattern- develops on uniform bedrock Radial pattern- develops on isolated volcanic cones or domes Rectangular pattern- develops on highly jointed bedrock Trellis pattern- develops in areas of alternating weak and resistant bedrock

Dendritic- uniform underlying bedrock; igneous rocks; flat-lying sedimentary rocks; most common

drainage patter on all scales; determined by direction of slope of land Rectangular- common in faulted or fractured igneous rock; often control patter of streams; guides directions of valleys Trellis- Most common in tilted and folded sedimentary or metamorphic rocks; formed by alternating less resistant and resistant layers e.g. Appalachians Radial- develops in isolated volcanic cones and domal uplifts; often localized Alluvial fans -

Fan-shaped deposits that accumulate along steep mountain fonts; Prevalent in mountainous and arid regions As mountain stream emerge onto a relatively flat low-land, gradient drops and a large portion of sediment load is deposited Bajada- coalescing alluvial fans *Sediments na dala ng river = Alluvium Alluvium: freshly eroded sediments carried by streams (coarse sediments) usually sandstone and conglomerate poor sorting, grading cone-shape Sibuyan Island; Laur, Nueva Ecija

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Lacustrine Lake- landlocked body of standing, non-marine water; ephemeral; excluding small ponds/puddles How to form lakes 1. -

Tectonic setting Lakes originate through:  Subsidence of land  Isolation of a part of the ocean either by local constructive processes of sediment deposition or by crustal uplift  Glacial erosion and deposition on the continents  Volcanoes- pyroclastic damming, crater collapse (caldera) through eruption or tectonic processes  Damming by landslides  Meteorite impacts

Tectonic Lakes- Laguna de Bay

Lacustrine -

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circular or elongate in plan view; lenticular in cross section Sediment sorting? Oxic and anoxic conditions Typical sequence- coarsening upward from laninated shales, marls and limestones to crossbeds of sandstones Quiet waters, energy: low, sedimentation : relatively slow Mud-sized sediments: laminated (beds < 1 cm in thickness) shales, marls to limestones and sandstones, well preserved fossils Varves- alternating oxic and anoxic (organic rich); represents 1 year

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Paludal -

swamps and marshes, energy: low, vegetations is high Fine clastic sedimentary rocks, similar to lakes Laminated, thinly bedded, burrows

Types of Sand Dunes: -

Aeolian -

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arid/dry climates: desert; semiarid climate: steppe “Dry” if precipitation is less than potential loss of water by evaporation Distribution: a. low latitude deserts: equatorial low and subtropical highs Middle latitude deserts: rainshadow effect Equatorial low: heated air at the equator rises and cools of while spreading Subtropical highs: air sinks, compressed and warmed Transportation: saltation and suspension Weathering and erosion:  two types of wind erosion: abrasion and deflation  Deflation: erosion of ground when dry, loose particles of dust and salt are lifted and blown away  Abrasion/sandblasting: shaping of solid rock surfaces by constant impact of grains by wind;  Loess: unconsolidated unstratified aggregation of small, angular mineral fragments

Transportation: Saltation and suspension (loess windblown silt) Some prominent features shaped through wind erosion  Blowouts- depressions produced by deflation  Desert pavements- closely packed layer of coarse particles (deflation)  Ventifacts- polished stones by abrasion  Yardangs- streamlined wind sculpted landform oriented parallel to prevailing wind Deposition  Dunes- mounds and ridges where sand is deposited as wind slow down  Deposition: leeward side (slip fave) and erosion stoss side migrating towards the direction of the wind -> Cross beds.

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Barchan dunes- crescent-shaped dunes. Hard ground surface, a moderate supply of sand and constant wind direction Transverse dunes- large field of dunes that resemble sand ripples on a large scale. Form in areas where there is abundant supply of sand and a constant wind direction Linear dunes- long straight dunes; form in areas with a limited sand supply and converging wind directions Parabolic dunes- are “U” shaped dunes with an open end facing upwind. Areas with abundant vegetation and constant wind. Most common in coastal areas. Star dunes- dunes with variable arms and slip face directions. Form in areas with abundant sand supply and variable wind direction.

Aeolian -

Lithology: well-sorted, cross bedded to planar bedded sandstones, polished clasts (rounded) Low vegetation (fossils: mummification)

Glacial Glaciers: thick ice mass that is moving slowly (cm/day) and is from accumulation, compaction and

recrystallization of snow; in areas where snow falls in winter > snow melt in summer note, that movement is fastest at the center -

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Zone of accumulation- more snow falls each winter than melts each summer Zone of wastage- all the snow from the previous winter melts along with some glacial ice Snow line Crevasses Basal slip Plastic flow Piggy Back (cracks -> crevasses)

Valley (Alpine) Glaciers: high elevation mountain tops, occupy valleys as streams of ice bounded by steep rock walls; valley glaciers can be long or short, wide or narrow, single or branching tributaries Continental ice sheets: larger scale than valley glaciers (Greenland and Antarctic); occupies 10% of Earth’s land area

Transitional Progradation- sediments advance towards the sea Retrogradation- sediments retreats away from the sea Transgression- landward migration of sea level (sea level rise) Regression- seaward migration of sea level (sea level fall) Delta -

Types of delta a.

Ice shelves: extensions of ice sheets on the adjacent ocean Glacial erosion Plucking- loosening and lifting sediments of all sizes; when ice melts, it leaves unsorted sediments generally called glacial drift Abrasion- like a sandpaper which smoothen the interface; if glacier carries rock fragments -> glacial striations

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Fjords- valleys going into the sea Glacial deposition: Moraines: ridges of till; some are common only to mountain valleys (lateral and medial) others are associated with areas affected by ice sheets or valley glaciers (end and ground moraines) a.

b.

Till (Tillite when lithified)- materials deposited directly by glacier; polished and scratched; if boulders in the till or lying free: glacial erratics (poorly sorted) Stratified drift- glacial meltwater; well sorted according to size (fluvial-like but clasts are polished)

prograding depositional bodies that form at a point where a river deposits in a lake or sea Similar to morphology to an alluvial fan, but deposition results from ocean reduction in velocity as a stream enters standing water/ocean.

River dominated (aka birdfoot delta)  large sediment volume  Lobate shape when moderate sediment supply  Elongated when sediment supply is large  Mississippi River Tide dominated  linear feature parallel to tidal flow and perpendicular to shore (sand bars)  Colorado River Wave dominated  smoothly arcuate; wave action reworks sediment  Much sandier than the other types of delta: beach ridges  Nile River

Beach Environment Beach- accumulation of sediment found along the landward migraine of the ocean Shoreline- contact between land and sea Shore- area that extends between the lowest tide level and the highest elevation on land affected by storm waves Sandy or pebbly material -

well sorted sand and pebbles either from terrestrial (e.g. volcanic fragments) or from

the seafloor (e.g. corals), smoothened and rounded by wave action

Marine -

Wave Erosion Wave Refraction- bending of waves; distribution of energy along shore since most waves travel toward the shore at an angle Wave impact is concentrated against the sides and ends of headlands (landmasses extending to the sea) and weakened at bays (body of water partly enclosed by land and has a wide opening) Longshore transport Longshore current: turbulent currents moving at an angle picks up sediments (back swash) and then deposit them (swash). Longshore drift: the movement of sediment along a beach by swash and backwash of waves that approach the shore obliquely Jettles interrupt the movement of sand causing deposition on the upcurrent side

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Shallow Marine Continental shelf -

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Spit- long ridge of sand deposited by longshore current and drift; attached to land at upstream end

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Tombolo- a sand or gravel bar that connects an island with the mainland or another island

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Coral reefs- composed of carbonate structures formed by carbonate secreting organisms; builds up on continental shelves

Types of Reefs a.

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continuous with the coastal plain; part of the continental margin that is between the shoreline and the continental slope

Continental shelf: Reef Environment

Erosion by sand- starved current occurs downcurrent from these structures

Lagoon

Continental Margins  Shallow-water areas close to shore  Shelf, slope and rise  ~15% of ocean floor Deep-Ocean Basins  Deep water areas farther from land Mid-ocean ridge  Submarine mountain ridge

Fringing reef- coral reef that is directly attached or borders the shore of an island or continent Barrier reefs- long narrow coral reef parallel to shore and separated by lagoon Atoll- continuous or broken circle of coral reef and low coral islands surrounding a central lagoon

Deep Marine shallow salt water body separated from the deeper sea by sandbar (exposed and submerged) or coral reef Quiet waters: fine silt and clays to mudstones and shales Overgrown with vegetation forming salt marshes, coal, peat swamps, algal mats or even evaporites

Tidal flats/mud flat -

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coastland wetlands found in sheltered areas such as bays, lagoon and estuaries; affected by high and low tide water levels Low energy with little fauna and flora (because of changing salinity) Lahat ng water in between high and low tide- brackish water

Continental Slope -

between the continental shelf continental rise (oceanic trench); sedimentation is low Carbonate compensation depth - depth at which CaCO3 dissolution >= CaCO3 precipitation below CCD: little to no carbonates

Continental Rise -

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gentle incline and generally smooth topography; between continental slope and abyssal plain May be cut by submarine canyons Turbiditic deposits- chaotic deposits of debris from shallow environments

Abyssal Plains -

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Pelagic: the ocean floor Fine-grained limestones, cherts, volcanic materials e.g. pillow lavas from submarine volcanoes Covered with pelagic mud with fine sand from distal turbidities

Features of the Deep Marine Seamounts- undersea volcanoes Guyots- tablemounts, rose above sea level in the past then eroded to a flat top by waves

Water table - upper limit of the zone of saturation Groundwater zone (zone of saturation; Phreatic zone) - where all of the open spaces in the sediments and rock are filled with water Porosity and Permeability Porosity a. b. c.

If above sea level: volcanic islands Groundwater -

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Freshwater- non-saline located beneath the ground Largest reservoir of freshwater that is readily available to humans All water:  Oceans (97%)  Freshwater (3%) Freshwater  Ice caps and Glaciers (79%)  Groundwater (20%)  Accessible Surface Freshwater (1%) Accessible Surface Freshwater  Lakes (52%)  Soil moisture (38%)  Water w/in living organisms (1%)  Rivers (8%)  Water vapor (8%)

Groundwater or Run-off -

Amount of freshwater beneath the ground a. Intensity of rainfall b. Steepness of the slope c. Nature of surface material d. Type and amount of vegetationStored in and transmitted through: 1. Spaces between grains of sediments and clastic rocks 2. Cracks or openings in rocks

Distribution of groundwater Unsaturated zone (Vadose zone) - pore spaces contain both air and water

Measures amount of water that can be held by rocks/sediments Volume of voids/total volume of material Affected by grain size, sorting, and grain packing  poorly sorted -> less porous  Cubic vs rhombohedral packing

Well-rounded coarse-grained sediments usually have higher porosity than fine-grained sediments, because the grains do not fit together well. Permeability a. b.

Ability to transmit fluids Degree of interconnection of voids in the material

Groundwater Transport Aquifer- stores and transmits sufficient amount of water freely Other confining units -

Aquitard- stores but slowly transmits water Aquiclude- stores but does not transmit water Aquifuge- does not store nor transmit water

Groundwater Transport An aquifer can be unconfined, perched or confined Unconfined aquifer -

bounded at the bottom by a confining unit\water rises up to the water table

Perched aquifer -

unconfined aquifer defined by a discontinuous confining unit local water table (usually above the main/regional water table)

Confined aquifer -

bounded at top and bottom by confining units water rises up to the piezometric water level (also called as the pontentiometric line or surface)

Form when the water table, confined aquifers or groundwater bearing fractures and cavities intersect the ground surface

Potentiometric surface/ Piezometric level -

Level to which water will rise ina well due to natural pressure in the rocks

Artesian wells -

When confined groundwater under high hydrostatic pressure is forced up to a level higher than the top aquifer  Wells tapping a confined aquifer  Analogy: water supply from elevated water tanks

Geologic work of groundwater Karst topography -

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Springs -

Cave

Landforms result from the solution of highly soluble (e.g. carbonate rocks, dolomite, gypsum, evaporites) by acidic groundwater; Takes place more rapidly at regions with high temperatures, lush vegetation, intense microbiotic activity -> CO2 Cockpit Country, Jamaica (Cockpit karst) Yangshuo, China (Tower karst (turmkarst)) Chocolate Hills, Bohol Palawan

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Karst topography: inside and out -

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a small, circular to oval, closed depression formed by: 1. Downward solution of limestone from the surface (solution sinkhole) 2. Collapse of the roof of a solution cavity (collapse sinkhole) May be bowl-, funnel-, or cylinder-shaped Dean’s Blue Hole, Bahamas New Zealand Tennessee Wright Park, Florida (1981)

Sinkhole Solution sinkhole Disappearing stream Cave entrance Collapse sinkhole Karst valley formed from coalescing sinkholes Giant spring Cave Collapse breccia

Problems associated with groundwater -

Sinkhole -

an elongate cavity in limestone produced by solution, aided by mechanical erosion of subterranean flowing water Study of formation and development of caves is known as speleogenesis Its shape is directed by lithology, by the pattern of joints, fractures, and faults, and by cave breakdown and evaporite weathering Lechuguilla Cave, New Mexico Speleothems - secondary mineral deposits formed in caves

Pollution (groundwater contamination) Saltwater intrusion (e.g. Hundred Islands, Alaminos) Land subsidence due to groundwater withdrawal  San Joaquin Valley, CA (19251975)  >5000 km2 in central California subsided up to 8.93 m due to over extraction of groundwater for agriculture  Mixed factors: camanava “enhance flooding”  Caloocan, Malabon, Navotas and Valenzuela (CAMANAVA)

Mixed factors CAMANAVA “enhanced”: flooding Excessive groundwater extraction -> Compaction of aquifers -> Land subsidence (3-9 cm/yr) -> Increased susceptibility to floods Does groundwater run out? -

Aquifers are recharged by the infiltration of rainwater or snowmelt from the ground

surface, but considering current situation: discharge > recharge Mass wasting -

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Downslope movement of rocks, regolith (unconsolidated material) and soil under the influence gravity Some mass wasting processes act very slowly; others occur very suddenly, often with disastrous results Dingalan, Aurora (debris flow) Real, Quezon Cherry Hills, Antipolo, Rizal Aug 3, 1999not debris flow Maco, Compostela Valley- debris flow

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Classification of mass wasting processes Types of movement (slope failures) -

Factors promoting mass wasting 1. -

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Slope Material resting on flat surface will not move under force of gravity On a slope, force of gravity is divided into 2 components: normal to surface and tangential to it If G+ (to downslope) > Gp (stay in place): mass wasting Water Angle of repose or steepest angle at which a pile of unconsolidated grains remain stable Dry, undersaturated soil, saturated soil Soil Cover Soil is more unconsolidated, and water percolating down may reach its contact with bedrock. This interface may serve as a sliding plane Thicker soil cover, greater volume of unconsolidated material Geologic features Type of rock Presence of joints or fractures Presence of bedding planes If direction of slope is the same as direction of planar features: daylighting slope

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Materials flow downhill mixed with water or air Slurry flows (solifluction, debris flow, mud flow) Granular flows (creep, earth flows, grain flows, debris, avalanches)

Types of materials -

Rocks, solid or debris

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sudden movement of rock, separated along fractures or bedding planes No fluidity in the motion, only bouncing, rolling, and free fall

Fall

Topple -

blocks of material fall over as a unit, similar to falling dominos

Slides (Translational) -

Ground shaking (e.g. earthquake or volcanic eruptions) Excessive rainfall that may saturate unconsolidated material Feb. 2012 Negros Occidental  Trigger: earthquake  Casualties: 51 dead, 62 missing

Sudden failure of the slope resulting in transport of debris down hill Fall, topple, slide, slump, spread and subsidence, flow

Water content and rate of movement

Triggers of Mass Wasting 1.

 Tracks and Intensity of all tropical storms  Saffir-Simpson Ground shaking (e.g. earthquake or volcanic eruptions) Excessive rainfall Jan 2012 Pantukan, Compostela Valley  Trigger: rain  Casualties: 38 dead; 16 injured, 37 missing

results when rocks (rock slides) and debris (debris slides) slide down a pre-existing surface such as a bedding plane, foliation surface or joint

Slump (Rotational slides) -

downward rotation of rock or regolith occurs along a concave-upward curved surface

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Leave arcuate scars or depressions on the hill slope

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Flow -

materials behave in a fluid manner and move rapidly

Mudflows -

Spread and subsidence -

there is compression, it is shortened, we are elevated, there is subduction

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Water content and rate of movement Slurry flows o

Creep -

very slow, usually continuous movement if regolith down slope

Solifluction -

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flowage at rates measures on the order of cm/yr of regolith containing water Produces distinctive lobes in hill slopes, where the soil remains saturated with water for long periods of time. Solifluction lobes, Kyrgyzstan

Earth flows -

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involve fine-grained materials that form a thick slurry and have a fluid motion; usually associated with heavy rains and move at velocities between several cm/yr and 100s of m/day Ooze rather than rush; form lobes rather than long streams like debris flows

Debris flows -

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occur at higher velocities than solifluction, with velocities between 1 m/yr and 100 mm/hr and often result from heavy rains causing saturation of the soil and regolith with water Sometimes start with slumps and then flow down hill forming lobes with an irregular surface consisting of ridges and furrows Hokkaido, Japan

Grain flows -

usually form in relatively dry material, such as sand dune, on a steep slope

A small disturbance sends the dry unconsolidated grains moving rapidly down slope

highly fluid, high velocity mixture of sediment and water that has a consistency ranging between soup-like and wet concrete Move at velocities greater than 1 km/hr and tend to travel along valley floors February 2006, Southern Leyte  Trigger: prolonged rainfall (La Niña weather)  Death toll: ~1,126 people December 2006, Mt. Mayon mudflows  Trigger: heavy rainfall (TY Reming | Int: Durian)  Death toll: ~1,266 people

Debris avalanches -

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very high velocity flows of large volume mixtures of rock and regolith that result from complete collapse of a mountainous slope Often triggered by earthquakes and volcanic eruptions Goodell Creek, USA (WA) Mt. St. Helens, USA (WA)

Mitigation Measures -

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hazard maps provide information about proper land use in certain areas identified to be prone to mass wasting “Hard” engineering measures (e.g. construction of features to stabilize slope) or “soft” measure (e.g. monitoring, information education campaign, earthquake drills)