What causes chemical changes in rocks?

Answer 1

Limestone rock is made of calcium carbonate in the form of the mineral calcite - tiny skeletons of microscopic organisms in shallow seas. On it's way through the atmosphere to earth, precipitation in the form of rain collects some carbon dioxide and produces a weak acid, known as carbon acid, of which calcite, and thus calcium carbonate, is vulnerable to. When this acid reaches the limestone structure, it causes the limestone to "dissolve". In large limestone structures, little groves are formed on the surface because of this. Wider groves are known as grykes and the structure that stands between grykes is known as a clint. The grykes allow water to sink below the surface allowing caves and potholes to form.

Answer 2

Limestone is calcium carbonate, CaCO3. The problem with carbonates is that, in acidic environments (such as acid rain), they tend to decompose to form a salt, water and carbon dioxide gas. For instance, if you add sulfiric acid, a common component of acid rain, to calcium carbonate; CaCO3(s) + H2SO4(aq) > CaSO4(s) + H20 (l) + CO2 (g)

Answer 3

Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere,biota and waters. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind and gravity.

Two important classifications of weathering processes exist - physical and chemical weathering. Mechanical or physical weatheringinvolves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. The second classification, chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals (also known as biological weathering) in the breakdown of rocks, soils and minerals.[1] As with many other geological processes the distinction between weathering and related processes is diffuse.

The materials left over after the rock breaks down combined with organic material creates soil. The mineral content of the soil is determined by the parent material, thus a soil derived from a single rock type can often be deficient in one or more minerals for good fertility, while a soil weathered from a mix of rock types (as in glacial, aeolian or alluvial sediments) often makes more fertile soil. In addition many of Earth's landforms and landscapes are the result of weathering processes combined with erosion and re-deposition.

Answer 4

How Caves Form in Limestone

The technical terms are introduced by capital initials.

Most of the world’s caves are in Limestone.

Caves need three materials: a soluble rock like Limestone or Gypsum, water and Carbon-dioxide (CO2).

Their host limestone also needs to be of appropriate physical structure and raised into hills, then subjected to reasonably consistent precipitation for many tens or hundreds of thousands of years.

Limestone is a sedimentary rock of which the world’s greater proportion was laid down in warm, relatively shallow, seas. The rock was laid in horizontal layers – Beds – separated by Bedding-planes which generally reflect geologically-brief changes in the environment. The suite of beds is known as a Formation, generally named after its “type area”.

Later continental uplift (tectonic processes) raise the formation along with its underlying rocks, usually tilting and folding it to at least some extent in the process. Since most rocks are brittle they cannot take much stress, and limestone beds crack into grids of fine fractures called Joints. The uplift and folding often also causes Faulting – major breaks with the rock mass one side of the Fault Plane being raised, lowered or moved horizontally past that on the opposite side. (Note: Plane – the “Fault Line” sometimes misused as a political metaphor is that of the fault-plane cutting the land surface.)

Now we have the hills, next we need rain-water that has absorbed atmospheric CO2 to create Carbonic Acid (weak, natural soda water in fact!). It may be augmented by acids from the soil, too. This solvent permeates through all those joints, bedding-planes and faults; flowing very, very slowly under considerable pressure applied by its depth, from its sinks on the surface to its springs at the base of the formation. In doing so, it dissolves the limestone (chemical weathering), creating meshes of tiny micro-conduits that over many tens of thousands of years coalesce and capture each other to form cave passages.

Once this happens, the rate of erosion can increase – though still to perhaps only a few millimetres per thousand years under generally temperate climates.

A cave, or a series within a cave system, that still carries its formative stream is called “Active”, and is still being developed.

Surface changes such as the valley floor being lowered by erosion, or down-cutting within the cave by its stream, changes the water’s route and the original, now dried-out, stream-way is called “Fossil” or “Abandoned”. Such passages may be filled with silt left by floods as the main flow gradually abandons them; or may become richly decorated with Speleothems – calcite deposits such as stalactites and stalagmites precipitated from ground-water still oozing through the joints in the limestone above the cave. In time such passages may start to break down as there is no stream to dissolve away slabs falling from the roof as permeating ground-water attacks the rock above.

In the end, surface lowering of the landscape as a whole, breaches and destroys the cave. Nothing is permanent in Nature!

Caves in limestone are also parts of Karst Landscape. i.e. a landscape developed by the dissolution of limestone, giving surface features like Dolines, Limestone Pavement, and in the tropics, distinctive hills such as those represented in Chinese Willow-pattern images. ‘Karst’ is from the Slavic word ‘Kras’, the name for its world type-area.

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The above is purely an introduction to a vastly more complex and subtle series of processes, of course, and you need to refer to appropriate text-books on geology and cave studies to learn them.

The scientific study of caves is Speleology – embracing geology, hydrology, Biology, Archaeology and other disciplines.

Simply visiting caves to enjoy them for their scenery and the physical and mental challenges they present, is called Caving, though you can’t study a cave unless you can negotiate its obstacles.

Answer 5

For the specific geology and development of any individual cave you will have to read the appropriate research papers on that region and its karst features; but if it's a karst cave, as most are, the essentials are:

How Caves Form in Limestone

This is such a common question on 'Answers' I wrote this single reply! The technical terms are introduced by capital initials.

Most of the world's caves are Karst features, i.e. primarily in Limestone.

Karst caves need three materials: a soluble rock like Limestone or Gypsum, water and Carbon-dioxide (CO2). The last two combine to form a weak acid that dissolves the limestone. For a fuller account:

The host limestone needs to be of appropriate physical structure and raised into hills, then subjected to reasonably consistent precipitation for many tens or hundreds of thousands of years.

Limestone is a sedimentary rock of which the world's greater proportion was laid down in warm, relatively shallow, seas. The rock was laid in horizontal layers - Beds - separated by Bedding-planes which generally reflect geologically-brief changes in the environment. The suite of beds is known as a Formation, generally named after its "type area".

Later continental uplift (tectonic processes) raise the formation along with its underlying rocks, usually tilting and folding it to at least some extent in the process. Since most rocks are brittle they cannot take much stress, and limestone beds crack into grids of fine fractures called Joints. The uplift and folding often also causes Faulting - major breaks with the rock mass one side of the Fault Plane being raised, lowered or moved horizontally past that on the opposite side. (Note: Plane - the "Fault Line" sometimes misused as a political metaphor is that of the fault-plane cutting the land surface.)

Now we have the hills, next we need rain-water that has absorbed atmospheric CO2 to create Carbonic Acid (weak, natural soda water in fact!). It may be augmented by acids from the soil, too. This solvent permeates through all those joints, bedding-planes and faults; flowing very, very slowly under considerable pressure applied by its depth, from its sinks on the surface to its springs at the base of the formation. In doing so, it dissolves the limestone (chemical weathering), creating meshes of tiny micro-conduits that over many tens of thousands of years coalesce and capture each other to form cave passages.

Once this happens, the rate of erosion can increase - though still to perhaps only a few millimetres per thousand years under generally temperate climates.

A cave, or a series within a cave system, that still carries its formative stream is called "Active", and is still being developed.

Surface changes such as the valley floor being lowered by erosion, or down-cutting within the cave by its stream, changes the water's route and the original, now dried-out, stream-way is called "Fossil" or "Abandoned". Such passages may be filled with silt left by floods as the main flow gradually abandons them; or may become richly decorated with Speleothems - calcite deposits such as stalactites and stalagmites precipitated from ground-water still oozing through the joints in the limestone above the cave. In time such passages may start to break down as there is no stream to dissolve away slabs falling from the roof as permeating ground-water attacks the rock above.

In the end, surface lowering of the landscape as a whole, breaches and destroys the cave. Nothing is permanent in Nature!

Caves in limestone are also parts of Karst Landscape. i.e. a landscape developed by the dissolution of limestone, giving surface features like Dolines, Limestone Pavement, and in the tropics, distinctive hills such as those represented in Chinese Willow-pattern images. 'Karst' is from the Slavic word 'Kras', the name for its world type-area.

@@@@@

The above is purely an introduction to a vastly more complex and subtle series of processes, of course, and you need to refer to appropriate text-books on geology and cave studies to learn them.

The scientific study of caves is Speleology - embracing geology, hydrology, biology, archaeology and other disciplines.

Simply visiting caves to enjoy them for their scenery and the physical and mental challenges they present, is called Caving, though you can't study a cave unless you can negotiate its obstacles. The enthusiasts are simply Cavers throughout the English-speaking world - you see "spelunkers" sometimes on 'Answers' but it's an old word invented by US cavers and originally neutral, but now derogatory..

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Answer 6

Physical (or mechanical) weathering of limestone occurs mainly through expansion of cracks and fissures from frost expansion which leads to further and deeper cracks and fissures. Plant roots seeking moisture may extend roots into limestone cracks and fissures, prying the rock apart.

Answer 7

Mainly acid rain ... but a nice volcanic explosion can produce both acids and bases of significant strength.

And just plane oxidation will change things.

Answer 8

I don't know ask your mother or ask your teacher! How am i suppose to know i came here for the answer and i am just 5

Answer 9

weathering