ASBOG Practice Exam

What significant feature is found in lava flows that assists in their reorientation?

1. Vesicular flow tops

2. Presence of sedimentary layers

3. Intrusions of granite

4. Color variations

The correct answer is: Vesicular flow tops

Lava flows are characterized by their distinct physical properties, and one significant feature that aids in their reorientation is the presence of vesicular flow tops. Vesicles are small gas bubbles that form during the cooling and solidification of lava. These vesicles affect the texture and density of the lava flow. When lava erupts and flows, varying rates of cooling can lead to the formation of these vesicles primarily at the surface, where gases can escape more freely. The structure created by these vesicular tops influences how the flow interacts with the environment, particularly in terms of adhesion to underlying surfaces and the ability to reorient during subsequent flows or tectonic activity. While sedimentary layers, granite intrusions, and color variations provide valuable geological information and may describe other aspects of the rock formations, they do not play a critical role in the physical dynamics of lava flow reorientation. Vesicular flow tops, however, serve as a practical characteristic directly linked to the flow's behavior as it moves across the landscape.