Which one of the following is formed when volcanic ash is carried by running water and is deposited as a sedimentary layer?

The correct answer is Tuff.

Key Points

• Tuff is a type of rock that forms from volcanic ash, which is ejected during a volcanic eruption and later compacted and cemented.
• When volcanic ash is carried by running water and deposited as a sedimentary layer, it solidifies into tuff over time.
• Tuff is categorized as a pyroclastic rock, which means it is formed from volcanic materials ejected during explosive eruptions.
• It is commonly composed of fragments of volcanic glass, minerals, and rock particles, often cemented together by fine-grained ash.
• Tuff is widely used in construction due to its light weight and ease of carving, and it has also been used historically for sculptures and buildings.

Additional Information

• Volcanic Ash: Tiny fragments of volcanic glass and mineral particles created during explosive volcanic eruptions. It can be transported by wind or water over long distances.
• Pyroclastic Deposits: These include any material ejected from a volcano during an eruption, such as ash, lapilli, and volcanic bombs, which may accumulate to form rocks like tuff.
• Basalt: A dense, dark-colored igneous rock formed from the rapid cooling of lava at the Earth's surface. It is unrelated to tuff, as it forms directly from lava rather than volcanic ash.
• Lapilli: Small, pea- to walnut-sized fragments of volcanic material that are ejected during an eruption. Unlike tuff, lapilli are not cemented into a solid rock.
• Slate: A metamorphic rock formed from shale under high pressure and temperature. It is unrelated to volcanic processes and should not be confused with tuff.