Geology Chapter 16: Groundwater Karst, and Caves

It is important to understand where the water flows in a karst aquifer. How is this done?

Dye tracing.

Karst: Sinking streams or blind valleys occur-

when a surface stream goes into a cave. Sometimes the streams sink gradually over distance.

Karst: Pollution of karst aquifers-

A common problem because the earth doesn't act like a filter as it would in, say, a sandstone. Ground water travel is concentrated and rapid, even though it is not visible. Farmers like to dump garbage in sinkholes.

Cave formations: Bacon

A stalactite shaped like a ribbon.

Porosity:

Ability of a rock to store water.

Permeability:

Ability of a rock to transmit water

An _____must have both porosity and permeability.

Aquifer.

Cave formations: Helectites

Are stalactites that twist and turn.

Caves: Cave life

Bats, salamanders, fish, shrimp, crickets, and spelunkers. Some of these are colorless and blind species, but most are pigmented.

Caves: Cave passages often follow_____ or the places where they cross

Bedding planes or joints.

Caves: Cave formations are made of_____

Calcite and form when water leaking into the cave loses its carbon dioxide.

Caves: Solution Scallops-

Can form on the surfaces of the limestone. Their size and orientation indicate the past water speed and direction, sort of like fossil ripple marks.

Aquifer: Poor aquifers (aquitards or confining layers)-

Clays or shales, unfractured nonporous rocks, poorly sorted sedimentary rocks.

Pumping wells create a _______in the water table.

Cone of depression

Cone of depression:

Cones of depression from nay wells can interfere, causing wells or streams to go dry, or revers gin the direction of groundwater flow. Entire aquifers can be pumped dry.

Karst: What does karst in other climates look like?

Conical or vertical towers, flat areas (poljes) or even limestone pinnacles.

Groundwater___ occurs where water table intersects the land surface. Water then exits the ground, typically by going into gaining streams, springs, or well pumping.

Discharge.

Caves: Shafts or dome pits-

Form from waterfalls which "drill" straight downward into limestone bedrock.

Caves: Lava tubes

Form when a stream of lava flows underneath its crust, leaving behind a hollow tube.

Cave formations: Columns

Form when stalactites and stalagmites merge into one structure.

Cave formations: Flowstone

Forms along walls or columns, where water trickles along a wall or surface.

Caves: Phreatic Tube-

Forms when a cave passage is completely submerged, and water can dissolve the ceiling as well as the floor and walls.

Cave formations: Dogtooth spar

Forms when large crystals of calcite grow, usually under water.

Cave formations: Selenite gypsum

Grows curly fibers that look like flowers.

Cave formations: Stalactites

Hanging down from the ceiling.

Karst:

Is a general word for landforms that develop from the dissolution of limestone. -Examples in the USA: are in Kentucky, western Tennessee, Missouri, southern Indiana, the Appalachians, and Texas. -Examples in SC: Santee State Park.

Caves: Cave development-

Is usually near the water table. If base level drops or the area is uplifted, the cave will then fill with air and might develop cave formations such as stalactites or stalagmites.

Cave formations: Rimstone

Lines the surface of a pool, forming small dams.

Karst: Karst windows-

Look like springs, but are just an unroofed stream passage in a cave.

Cave formations: Cave popcorn or coral

Looks like its name.

Cave formations: Cave Pearls

Occur when calcite encrusts small stones, where water falls and tumbles them around.

Karst: Springs

Occur where the underground streams come back (resurge) to the surface due to arrival at abase level or perhaps an impermeable layer of rock.

When pollution leaks underground, it creates a contamination ____

Plume: for more details refer to chapter 16 notes on blackboard.

Groundwater__ occurs where water infiltrates into an aquifer, usually in high areas.

Recharge.

Karst: Dry valleys

Remain on the surface where the stream flowed at one time, or just now flows occasionally during floods.

Caves: Breakdown-

Rocks that have fallen from the ceiling. This almost always happens shortly after the cave becomes filled with air, and the water can no longer support the ceiling. The presence of breakdown does not mean the cave is dangerous. This does NOT apply to mines.

Karst: Karren

Small rills and ridges that develop on an exposed outcrop.

Cave formations: Soda Straws

Small stalactites that look like their name.

The water table generally follows the shape of the _____

Topography. Where it is close to the ground you may find swamps or springs.

Karst: sinkholes

Usually dot the karst surface. They can form rapidly by cave collapse, or gradually by dissolution over geologic time.

Confined aquifer:

Water flows under pressure.

Aquifer: Good aquifers-

Well sorted sands or gravels, highly fractured rocks, cavernous limestones.

Artesian Wells:

Wells drilled into confounded aquifers.

Karst: Cenotes

are steep -sided sinkholes that intersect the water table-natural wells.

Karst: Natural Bridges

are the remains of a cave that has eroded away except for one small part of the roof.

Flowing wells:

occur if the pressure surface of the aquifer is above ground level. Artesian walls are common on the coastal plain.

Karst: Estevelles-

sometimes act like springs, sometimes like sinking streams.