Physical Geology Exam 5 Study Guide Ground Water GROUNDWATER AQUIFERS - An underground, water bearing geologic unit (or units). An aquifer may consist of rock, unconsolidated sediments, and may be confined or unconfined.

Unconfined – like underground storage basins in porous materials. Groundwater levels are free to rise or fall. Confined – a layer of water-bearing material sandwiched between two layers of much less pervious material. Artesian conditions occur when a well, or other conduit, exists that penetrates a confined aquifer; the groundwater (under pressure) rises to a level higher than that of the confined aquifer. Artesian systems may be flowing (the pressure is such that water comes out of the ground) or non-flowing. Watertable – The surface between the zone of saturation and the zone of aeration or unsaturated zone. The term watertable is used only for unconfined aquifers. PIEZOMETRIC/POTENTIOMETRIC SURFACE - An imaginary surface representing the total head of ground water and defined by the level to which water will rise in a well. This term is used for confined aquifers. Watertable Well – a well constructed so that the screened portion straddles the watertable during the majority of the year.

Piezometer – a well constructed with the screened segment entirely below the watertable at all times.

Pressure Head (or just, “head” ) - at a given point in a flow system is the height to which water will rise in a piezometer inserted down to that point. Head at a given point in an aquifer is equal to the vertical distance of that point below the watertable. The mid-point of a screened well is used as the “depth of reading”. WELL NESTS -Within an aquifer the primary component of flow is usually lateral. However, there may also be a vertical component of groundwater flow. A well nest (a cluster of three or more monitoring wells) is used to evaluate the vertical component of groundwater flow. Aquifer porosity – A measure of the voids within an aquifer, usually expressed as a percentage. Hydraulic conductivity (K) – A property of the aquifer that depends upon the size and number of pores. It is a measure of the ease that groundwater may pass through the aquifer. Aquifer permeability (k) – A measure of the ability of a porous material to allow fluids to pass through it. Hydraulic gradient (i) - The slope of the watertable or potentiometric surface. Aquitards – A low permeability layer. Aquicludes – A layer that will not permit the flow of water. POROSITY - The percentage of the total volume of the material that is occupied by pores. The “packing” and shape of the grains is important.

Permeability of a porous medium refers to the ease with which a fluid will pass through it. However, the permeability of a medium also depends upon characteristics (namely, viscosity) of the fluid passing through.Permeability is usually identified by a lower case “k” (versus an upper case “K” for hydraulic conductivity). Aquitard – a layer that is sufficiently permeable to transmit water vertically, but not permeable enough for lateral transport of groundwater. An aquifer bounded by one or more aquitards is called a “leaky aquifer” or a semi-confined aquifer.

Aquiclude – a confining layer that is essentially impermeable.

Perched Watertable - is a localized zone of saturation, usually created by the presence of an underlying aquitard or aquiclude. Cone of Depression - when a well is being pumped, the aquifer immediately around the well is dewatered. Ogallala Aquifer underlies approximately 225,000 squaremiles in the Great Plains region, particularly in the High Plains of Texas, New Mexico, Oklahoma, Kansas, Colorado, and Nebraska. The depth of the aquifer from the surface of the land, its rate of natural thickness, vary from region to region. The aquifer has long been a major source of water for agricultural, municipal, and industrial development. Use of the aquifer began at the turn of the century, and since World War II reliance on it has steadily increased. The withdrawal of this groundwater has now greatly surpassed the aquifer's rate of natural recharge. Some places overlying the aquifer have already exhausted their underground supply as a source of irrigation. Other parts have more favorable saturated thicknesses and recharge rates, and so are less vulnerable. AQUIFER SUBSIDENCE - When water is removed from the pore spaces of an aquifer at a rate that exceeds recharge, the pore spaces become filled with air and thus the aquifer materials behave like a compressible material.If enough water is removed, the pore space is minimized and the aquifer collapses, resulting in subsidenceat the land surface.

KARST TOPOGRAPHY - Named after the Krs Plateau in Slovenia, on the northeastern shore of the Adriatic Sea. Karst Topography is usually dominated by sinkholes (or “sinks”), and lacks surface drainage systems. Sinkholes: Form by the dissolution (by descending rainwater and/or groundwater) of carbonate bedrock. Sinkholes may form slowly, from the top on down, or quickly, after the roof of a subterranean cavern collapses. Tower Karst: This topography forms in wet tropical and subtropical regions characterized by highly jointed limestone bedrock. Dissolution of bedrock leaves behind “towers” (steep sided hills) of bedrock containing interconnected caves and passageways.

Glaciers Glacier - A large mass of ice formed on land by the compaction and recrystallization of snow, creeping downslope or outward due to the stress of its own weight, and surviving from year to year. Valley/Alpine Glacier – A glacier in mountainous terrain, usually originating in a cirque and flowing down a valley previously made by a stream. Ice Sheet – A glacier of considerable thickness and more than 50,000 square kilometers in area, forming a continuous cover of ice and snow over a land surface, spreading outward in all directions and not confined by the underlying topography. Ice Shelves - Ice sheets extend into adjacent oceans, forming enormous layers of floating ice. (The Ross Ice Shelf in the Antarctic is the size of Texas) Ice Cap – A dome-shaped or platelike cover of perennial ice and snow, covering the summit area of a mountain so that no peaks emerge through it, or covering a flat landmass such as an Arctic island; spreads outward in all directions; <50,000 square kilometers. (Greenland) Piedmont Glacier - A glacier formed by coalescence of two or more valley glaciers at the base of a mountain range. Firn – a material transitional between snow and glacier ice. 1. Snowfall. 2. Destructive metamorphism – crystals become rounded. in temperate glaciers, wet mmfsm – water, ice, vapor in polar conditions, dry mmfsm – ice, vapor 3. Compaction due to subsequent snowfalls leads to sintering, the process of bonding individual crystals to one another. 4. The result is recrystallized material called firn. “Overburden compaction, due to layers of snow and firn in excess of 50 ,is sufficient to turn firn into glacial ice.”

The upper portion of a glacier behaves in a brittle fashion, and is called the zone of fracture. Firn behaves as a brittle solid until it exceeds a depth of 50 meters, at which point it exhibits plastic flow. Plastic flow – layers of ice molecules slide past one another, creating flow. Basal slip - meltwater beneath a glacier acts as a lubricant, allowing the bottom of the glacier to slip along bedrock. Greenland: A glacier called Kangerdlugssuaq, is moving at a rate of 8.7 miles a year, making it (as of 2005) one of the world's fastest-moving glaciers. In the late 1990s, it was moving at about 3.5 miles a year. Note: 8.7 mi/yr = +/- 125 ft/day!

Plucking – Meltwater beneath a glacier penetrates fractures in underlying bedrock. As the meltwaterfreezes in the cracks it expands, lifting fragments of bedrock up, which are then incorporated into the glacial ice. Abrasion – Glacial ice, loaded with rock fragments, gravel, and sand, abrade the underlying bedrock. Glacial abrasion may produce linear grooves in bedrock called Glacial Striations.

Glacial Valleys… - Are “U” shaped; - Tend to be straight; - Have hanging valleys; - Begin with a cirque that perhaps contains a tarn; - May contain “pater noster” lakes.

Col – A high, sharp-edged pass in a mountain range formed by the headward erosion of two cirques, or a saddle-like depression in the crest of a mountain ridge. Fjord – A long, narrow U-shaped valley along a mountainous coast. A fjord usually represents the seaward end of a deeply excavated glacial valley that was partially submerged by drowning after melting of the ice.

Arete – A rocky, sharp-edged ridge or spur. Formation: 1. Two cirques are enlarged, with the divide between becoming thinner. 2. Two parallel glaciers pluck the divide between until the divide very narrow.

Horn - A high, pyramidal peak with steep sides formed by the intersecting walls of three or more cirques. The Matterhorn (Wyoming) is the type example. Roches Moutonnees – A glacially sculpted knob of bedrock, with its long axis oriented in the direction of ice movement, an upstream (stoss) side that is gently inclined, rounded, and striated, and a downstream (lee) side that is steep, rough, and hackly. Glacial Drift - Material transported by glaciers or icebergs. This material is typically mechanically weathered (versus chemically weathered), and is usually divided into:

Till – material deposited directly by glaciers, Glacial till is usually poorly sorted and individual fragments are mechanically weathered. Stratified Drift – material deposited by meltwater from glaciers.

Moraine - a mound or ridge of unstratified glacial drift, deposited by direct action of glacial ice. Lateral moraine (sides) Medial moraine (middle) Recessional moraine (end/during retreat stabilization) End/terminal moraine (end/furthest point of advance) Ground moraine - An accumulation of till after it has been deposited or released from the ice during ablation, to form an extensive area of low relief devoid of linear elements. Ablation – all processes by which snow and ice are lost from a glacier. Drumlin – a low, smoothly rounded, elongate hill of compact glacial till, built under the margin ice and shaped by its flow. Composed of till, Asymmetrical hills, 15 to 50 m high up to 1 km long, Gently sloping side points in the direction the ice moved, Occur in groups called drumlin fields.

Outwash Plain -A broad, gently sloping sheet of outwash deposited by meltwater streams flowing in front of or beyond a glacier. Kettle - A depression in glacial drift, especially in outwash. A kettle forms when a block of ice, buried in the drift, melts and the drift settles into a depression. Kame - A mound, knob, or short irregular ridge composed of stratified sand and gravel. This material is deposited within, or on top of, the ice, or by a subglacial stream as a fan or delta at the margin of a melting glacier. Kame moraine – an end moraine containing numerous kames. Kame terrace – a terrace-like ridge formed between a melting glacier and a higher valley wall or lateral moraine. Esker - A serpentine ridge of roughly stratified gravel and sand deposited by a stream flowing in or beneath the ice of a stagnant or retreating glacier.

Subsidence: Weight of glacial ice may compress or down-warp the Earth’s crust. Isostatic Rebound: Following melting of glacial ice (unloading), the Earth’s crust rebounds upward. Swedish High Coast – This area has also been largely shaped by the combined processes of glaciation, glacial retreat and the emergence of new land from the sea. Since the last retreat of the ice from the High Coast 9,600 years ago, the total rebound has been approximately 285 meters. The rate of rebound is approximately 0.9 meters per century. Kvarken Archipelago – Consists of 5,600 islands featuring unusual ridged washboard-like moraines called ‘De Geer moraines’. These were formed by the melting of the continental ice sheet, 10,000 to 24,000 years ago. The Archipelago is continuously rising from the sea. As a consequence islands appear and unite, peninsulas expand, and lakes evolve from bays and develop into marshes and peat fens.