Lake Formation & Classifications

Terminal Moraine

A terminal moraine is a ridge of glacial debris deposited by a glacier at its farthest extent. This accumulation of rock, sand, and clay, known as till, is pushed forward by the leading edge of the ice and dumped when the glacier stops advancing.

• Unstratified structure: The sediment has no neat layers or visible bedding because it was dumped directly by melting ice rather than flowing water.

• Arc shape: The ridge curves gently across a valley, mirroring the curved shape of the glacier's front edge

Ice-Scour

form when massive sheets of moving glacial ice gouge and depress weak spots in the bedrock, creating depressions that fill with meltwater when the glacier retreats

Irregular Basins: They often feature uneven, rocky bottoms and irregular shorelines rather than smooth, uniform shapes.

Kettle Lake

• A retreating glacier leaves behind large, stationary chunks of ice. Meltwater streams deposit layers of sand, gravel, and rock debris around or completely over these ice blocks. The buried ice melts slowly over hundreds or thousands of years, causing the overlying sediment to collapse inward and create a depression called a kettle hole. Groundwater, rain, or melting snow fills the pit.

• Typically round or oval shorelines. Usually shallow, frequently less than 10 meters (33 feet) deep, though some can reach depths over 45 meters

Cirque

• accumulated snow compacts into ice, forming a small alpine glacier called a cirque glacier: As the gravity-driven glacier moves, it rotates downward. It plucks rocks from the back wall (making it steeper) and uses those rocks to scour out the floor of the hollow (deepening it into a Rock debris eroded by the glacier accumulates at the lower edge of the bowl, forming a natural lip or wall called a moraine. glacier melts away, water fills the deeply hollowed-out basin.

Bowl and circular shape. Three nearly vertical cliff walls, one lipped wall on downslope side. Deep, at high altitudes.

Tectonic

Movement of the earths crust to create basins. Very old, big, and deep

Graben

form when a block of the Earth's crust drops down between parallel normal faults, creating a deep depression that fills with water

Extremely old, large, and deep. Steep cliffs on edges.

Tilted fault block

form when crustal blocks pull apart and rotate along a fault line, creating an asymmetric, half-graben depression that fills with water

One gently sloping shore, and one steep shore. Wedge-shaped basin. Shallow at the backslope. Long narrow traughs parallel to the faults.

Caldera

forms when a massive volcanic eruption empties an underground magma chamber, causing the ground above it to collapse into a bowl-shaped depression that eventually fills with rain and snowmelt

Large, steep walls. Inward facing slopes

Maar

a broad, low-relief volcanic crater filled with water, formed by a violent steam explosion when rising magma meets groundwater or permafrost

Broad (1000s of meters wide), shallow crater. Ring-shaped rim.

Lava dammed

form when a stream or river valley is blocked by a hardened basaltic lava flow, trapping water behind the volcanic barrier

• They often feature narrow, elongated, or branching shapes that mirror the flooded river valleys and canyons they occupy. (often short-lived as they fill with sediment)

Oxbow

a U-shaped or crescent-shaped body of water formed when a wide bend, or meander, of a river is cut off from the main channel

Floodplain

• Oxbow Lakes

• Channel Abandonment (cutoff): Shift in the active river channel leaves behind segments of old channels in the floodplain.

• Levée and Depression Impoundment: Natural levees build up alongside active channels during floods, trapping water and creating depressions or impeded drainage zones behind them.

• Scour and Deposition: High-energy flood events scour depressions or deposit sediment unevenly, creating basins filled by overbank flow or local runoff.

Elongated, irregular, crescent shaped. Very shallow.

Subsidence (sinkholes)

form when a surface depression created by the collapse or dissolution of soluble bedrock (limestone, gypsum, or chalk) intersects the local water table and fills with water

High depth relative to surface area. Seep sides. Funnel or U-shaped vertically.

Permafrost thaw

form when ice-rich ground thaws, causing the land surface to subside and meltwater or precipitation to accumulate in the resulting depression

Expanding deep-ice lakes feature broad, gently sloping, or inclined marginal benches (100+ meters wide), while shallow lakes maintain abrupt or concave profiles

Animals (buffalo, beavers, alligators)

Over time depressions are made by the weight of the animals. Shallow, not super large.

Meteor

Formed from water filling circular depressions left by meteor strikes. Highly circular. Depth ranges on how hard the meteor hit. Often topographically isolated

Farm & Residential Ponds

Characteristic	Farm Ponds	Residential Ponds
Primary Shape	Uniform geometric (square, rectangular, or circular) to maximize volume.	Irregular, organic, and curving to mimic natural water bodies.
Average Depth	8 to 15 feet (deep enough to prevent total freezing and reduce evaporation).	4 to 8 feet (shallower, though deep enough to prevent winter fish kills).

Quarries

form when open-pit mining operations dig below the local water table and abandon the site, allowing groundwater seepage, rainwater, or surface runoff to fill the excavated pit

High relative depth (to natural lakes), steep uniform sides. Small littoral and marsh zones. Meromixis (incomplete mixing) . Small surface area.

Stormwater Ponds

artificial water bodies formed by excavating land in urban areas to capture, store, and treat rainwater runoff

Shallow and small. Urban areas.

Watershed

A region of land within which water flows down into a specified body. ‘catchment’ or ‘containment basin’

Oligotrophic

• Low Nutrients: Very small amounts of phosphorus and nitrogen limit biological productivity.

• High Clarity: Water is exceptionally clear because there is very little algae or plant growth.

• Abundant Oxygen: High dissolved oxygen levels exist throughout the entire water depth.

• Substrate: Lake bottoms are usually firm, sandy, or rocky rather than mucky

Eutrophic

• High Nutrients: Abundant nitrogen and phosphorus fuel rapid plant and algae growth.

• Murky Water: Dense phytoplankton and suspended particles reduce water clarity and transparency.

• Low Oxygen (Hypoxia): Decomposing dead algae consume large amounts of dissolved oxygen, creating stress for aquatic life.

• Soft Substrate: The lake bottom is typically covered in thick, mucky organic sediment.

Volcanic

Volcanic activity creates basins through collapse or damming. Can be very round, typically steep sides, lava flow can block valleys

Reservoir

Man-made lakes with a dam to store water.

• Shape (Morphometry): Reservoirs often have a dendritic (tree-like) shape with long, narrow arms stretching up the flooded river valleys, unlike natural bowl-shaped or circular lakes.

• Depth and Location: The deepest part of a reservoir is usually right next to the dam wall, while the shallowest parts are far upstream where the original river flows in.

• Water Level Fluctuation: Water levels change often and dramatically based on human use

Mesotrophic

• Nutrient Levels: Contain moderate amounts of phosphorus and nitrogen, supporting balanced plant and animal life.

• Water Clarity: Generally clear with moderate transparency, showing Secchi disk visibility depths between 2 and 5 meters

• Biological Productivity: Support healthy, diverse populations of submerged aquatic plants, algae, and fish, with occasional minor algae blooms in warmer months.

• Oxygen Content: Moderately well-oxygenated, though deep mesotrophic lakes may experience low oxygen in the bottom layer (hypolimnion) by late summer

Dimictic lakes

Mix or "turn over" twice a year—once in the spring and once in the fall—when the water reaches a uniform temperature and density. These are very common in temperate regions

Cold Monomictic

Found in polar or high-altitude regions with ice cover; they mix during a short summer period when water stays at or below 4°C. Mixes once

Warm Monomictic

Ice-free lakes that remain stratified most of the year and mix during the winter when surface water cools. Mixes once

Polymictic

Mix continuously or frequently throughout the year. These are typically shallow lakes where wind easily disrupts any temporary thermal layers

Oligomictic

Mix rarely and irregularly, often only once every few years. These are usually deep, stable tropical or subtropical waterbodies

Meromictic Lakes

Do not mix completely. They feature a permanent, dense, and oxygen-depleted bottom layer (monimolimnion) that never circulates with the upper layer (mixolimnion)

Amictic

Perennially sealed off by thick ice cover and never mix.