Science Olympiad Dynamic Planet Practice Test

What type of sediment commonly accumulates in a backarc basin?

1. Well-weathered terrestrial sediments

2. Poorly weathered volcanic rock fragments

3. High-latitude glacial deposits

4. Deep ocean marine sediments

The correct answer is: Poorly weathered volcanic rock fragments

The accumulation of poorly weathered volcanic rock fragments in a backarc basin is primarily due to the geological processes associated with tectonic activity and volcanic eruptions in these regions. Backarc basins form behind a volcanic arc and are often characterized by significant volcanic activity, which contributes to the production of volcanic ash and pumice. These materials are typically less weathered compared to sediments found in more stable environments, leading to their prevalence in this type of basin. The formation of backarc basins usually results from extensional tectonics, where the lithosphere is pulled apart, allowing for the accumulation of sediment in a recently formed depression. This setting is conducive to the deposition of volcanic materials, as ongoing eruptions and weathering processes contribute fresh volcanic rock fragments that accumulate over time, creating a layer of poorly weathered sediments. Other sediment types mentioned in the options, such as well-weathered terrestrial sediments and high-latitude glacial deposits, are more characteristic of different environments, such as river valleys or areas affected by glaciation. Deep ocean marine sediments are typically found in more stable oceanic settings and not in the more dynamic geologic conditions present in backarc basins, making the accumulation of poorly weathered volcanic rock fragments a defining characteristic of these