Which weathering reaction creates limestone caverns

Dolomitic limestone, a sedimentary rock, was formed over millions of years through chemical reactions generated by these early organisms. As time passed the limestone, which is permeable and soluble, was eroded by water. Weak carbonic acid in rainwater, reacting with the chemicals in the rock, dissolved and eroded away the limestone as the water filtered into the underlying depths of sediments.

Large hollow solution cavities were formed in the limestone in this way. Many cavities occur at various depths in a cave system due to the continual seepage and flow of the mildly acidic water through the deposits, while underground rivers may eventually carve their way through a mountainside, creating openings and entrances to the outside.

Many beautiful structures — including stalagmites and stalactites — form inside caves as carbonic acid, carrying limestone, drips through cave roofs and onto their floors. The weathering of rocks by chemicals is called chemical weathering. Rainwater is naturally slightly acidic because carbon dioxide from the air dissolves in it.

Minerals in rocks may react with the rainwater, causing the rock to be weathered. Some types of rock are easily weathered by chemicals. For example, limestone and chalk are mostly calcium carbonate. Layers of calcite build up into fluted curtains. Helictites seem to defy gravity. They grow when water slowly seeps through porous roof or wall surfaces, producing tiny droplets that precipitate calcite in the form of fine tubes with minute internal channels. The water flows through the tubes by capillary action, and changes in the direction of growth may be due to blockages in the internal channels.

As the calcite grows from the tip at various angles, interesting twisted shapes result. Flowstone forms from layers of calcite deposited when thin films of water flow down walls and across cave floors. Some resemble 'frozen waterfalls'. Flowstone often forms over gravel and silt left behind by underground rivers. When this material is washed away to leave an undercut, canopies of flowstone are left unsupported.

Rimstone dams build up on slopes as slow-moving water flows over them. Bumps on the sloping surface promote turbulence and assist carbon dioxide loss.

The resulting low walls can hold back water to form a pond. Calcite crystals grow as 'dog-tooth spar' when caves or smaller cavities are filled with still water.

Cave Formations Speleothems In limestone caves, after the natural process of erosion and excavation, a simple but slow natural process is responsible for the decoration of the bare, dull walls. As water drips slowly from the roof of the cave, it deposits a microscopic ring of calcite crystal. These rings continue to build and can form straws many centimetres long. Stalactites are also formations that grow downwards from the cave roof.

Nearly all stalactites start their life as a straw. When the straw becomes blocked with calcite or impurities, a stalactite starts to develop and thicken over the years, from the solution which runs down its outer surface.

Stalagmites are solid dripstones that grow upwards from the cave floor, from each drop of water from the roof or from stalactites overhead. Columns or Pillars are formations that develop from stalactites or stalagmites that extend from floor to roof. Flowstone : Shawls - Water reaching the roof of a cave does not always form drops. Sometimes it trickles down a rockface, depositing a narrow strip of calcite, that eventually results in a thin sheet, growing at an angle from the wall.

Shawls often contain interesting folds, which occur because the initial trickle turned from side to side in its downward path along the rockface.