ASBOG Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

Compaction and cementation are essential processes that turn loose volcanic ash into solid rock. When volcanic ash is deposited, it can accumulate in layers. Over time, the weight of the layers above compresses the underlying material, leading to compaction. As this occurs, water carrying dissolved minerals can also infiltrate the spaces between the ash particles. As the water evaporates, the minerals precipitate and act as a natural cement. This cements the ash particles together, forming a coherent rock known as tuff or other volcanic lithologies.

Unlike the other processes mentioned, compaction and cementation specifically describe the transformation of loose sediment (in this case, volcanic ash) into solid rock, highlighting the importance of physical and chemical bonding in sedimentary processes. Melting and solidification generally refer to the formation of igneous rocks from molten material, while weathering involves the breakdown of existing rocks rather than their consolidation. Crystallization pertains to the formation of crystals from a liquid or gas, which is crucial in the formation of igneous and metamorphic rocks but does not directly address the transformation of ash into solid rock. Thus, compaction and cementation are the key processes in this context.