Question

In which of the following types of rock are caves most likely to form? A. limestone C. granite B. sandstone D. basalt

Short answer

Caves are most likely to form in limestone.

Step-by-step solution

Understand Cave Formation

Caves are natural voids in the ground that are most commonly formed by the weathering of rock and can occur in different types of rock formations. The most common caves form through the process of chemical weathering, which involves the dissolution of rock by water.

Evaluate Rock Types for Solubility

Consider the solubility of the rocks in question. Limestone, composed mainly of calcium carbonate, is highly soluble in weakly acidic water (such as rainwater mixed with carbon dioxide forming carbonic acid). Granite, sandstone, and basalt are much less soluble.

Identify the Type of Rock Most Likely to Form Caves

Since limestone is highly prone to dissolution by water, it is the rock type most commonly associated with the formation of caves. The dissolution leads to the creation of cavities and eventually caves.

Key concepts

Chemical Weathering

Chemical weathering is a natural process where rocks are broken down through chemical reactions. This is distinct from physical weathering, which involves the mechanical breakdown of rocks. Chemical weathering happens when minerals in the rock react with substances like water, oxygen, acids, or base solutions.

Water plays a pivotal role in this process. As rainwater falls, it combines with carbon dioxide from the atmosphere, forming a weak carbonic acid. This slightly acidic water can infiltrate rocks, initiating the weathering process.

• The most vulnerable rocks have minerals that readily react chemically.
• This process not only breaks down rocks but also alters their chemical structure.

Chemical weathering can significantly reshape landscapes over long periods of time, leading to features such as soil development and caves.

Limestone Solubility

Limestone is a sedimentary rock primarily composed of calcium carbonate (CaCO₃). Its solubility is one of the key factors that make limestone highly susceptible to cave formation. When rainwater falls and collects carbon dioxide, it forms carbonic acid. This weak acid can dissolve limestone readily.

This process results in the rock slowly breaking down and creates underground channels and voids that can eventually evolve into caves. Limestone's high solubility in acidic conditions distinguishes it from less soluble rocks.

• Limestone dissolves consistently along fractures, bedding planes, and layers.
• This dissolution creates characteristic features such as sinkholes, springs, and stalactites.

The ability of limestone to dissolve significantly contributes to the prevalent formation of limestone caves around the world.

Rock Dissolution

Rock dissolution refers to the process of acid or water gradually breaking down and dissolving rocks. This process is crucial in forming caves, especially those in limestone. When water, often containing weak acids, comes into contact with soluble rocks, it reacts with them.

The minerals in these rocks interact with the water's acidity, causing the minerals to be carried away and slowly enlarging fractures and natural openings. Over time, these processes can lead to the creation of substantial cave systems.

• Dissolution preferentially follows paths of least resistance like joints and bedding planes.
• The rate of dissolution varies based on the rock type and acidity of the water.

Rock dissolution is vital for understanding geological formations and contributes to notable features such as karst landscapes, caves, and underground water reservoirs.