Underground features of a limestone landscape
CAVE SYSTEM
A cave or caves with a complex network made up of interconnected chambers and passages that make up an underground drainage system
CAVE
A natural opening in the rock which is large enough to be entered by a person and extends to points where daylight does not penetrate. Underground rivers dissolve the limestone and carry it away to leave these passageways which can be full of water during periods of heavy rainfall.
GROUNDWATER
Water seeping down from the surface saturates the bedrock. Groundwater is the name given to the water where all the pore spaces and joints are filled with water .
SUBSURFACE DRAINAGE
Many rivers and streams flowing onto a limestone outcrop will lose almost all water to the underground. The water can flow directly into caves or can be lost through fissures, joints, and sinkholes. The rivers can also have a series of sinking points, and flow is often intermittent.
WATER TABLE
The water table is the upper surface of the saturated rock. If there is very heavy rain then the water table can rise to surface level.
IMPERMEABLE (IMPERVIOUS) ROCK
This is rock where there are no joints or the pores are so small that water cannot pass through. Clay is the best example of an impermeable rock.
STALACTITE
This is a calcium carbonate deposit like an icicle formed in caves by chemical precipitation from drips or thin films of water.
Stalactites (from the ceiling) are built up from many successive growth layers and almost always have pointed tips. Now, exactly why these deposits are left behind is sort of tricky.
Follow closely. As the drop of water hangs from the ceiling, it loses some of its carbon dioxide. This makes it less acidic. That means that it can't hold all of the dissolved minerals that it had picked up, on its way through the cracks above. The drop leaves a few crystals of the mineral calcite behind, and a stalactite begins to grow. Drop after drop, over hundreds and thousands of years, can end up leaving some big stuff! Our new cave is filling back in with rock from above, and tiny cracks up there are growing into more new cave!
STALAGMITES
When water containing dissolved limestone falls to the floor of a cave some of the calcite precipitates out. This build up of deposits forms a mound growing up from the floor. (StalaGmites are on the Ground.) Stalagmites take on a variety of forms, from tall, spindly "broomsticks" to broad, flat disks to ornate, multi-tiered towers . Shape is determined largely by drip rate, ceiling height, cave atmosphere conditions, and the carbonate chemistry of the drip water solution.
COLUMN
When a stalactite and a stalagmite grow so much that they join together to form a vertical limestone pillar from floor to ceiling.
CURTAIN
When water seeps down through a hole it produces a stalactite. When water seeps down along the length of a joint it produces a type of stalactite which resembles a curtain of calcite. They can be very thin and fragile and after many years they can reach the ground.
UNDERGROUND STREAMS
Streams flow underground when the limestone lies over an impermeable rock. The water which has seeped vertically down through the limestone can travel horizontally when it can sink no further. If the cave carrying the stream fills up during a period of very heavy rain then the stream can erode away the roof enlarging the cave even more.
