ASBOG Practice Exam

What internal structure in lava flows can be critical for reorienting them?

1. Alternating dense flow rock with vesicular flow top rocks

2. Uniform density throughout

3. Presence of intrusive rocks

4. Magmatic layering

The correct answer is: Alternating dense flow rock with vesicular flow top rocks

The internal structure of lava flows, particularly the presence of alternating dense flow rock with vesicular flow top rocks, plays a crucial role in understanding and reorienting these geological formations. Dense flow rocks, which are formed from the solidification of lava, typically exhibit lower porosity and higher density. In contrast, vesicular flow tops are characterized by gas bubbles trapped during solidification, resulting in a more porous and lighter structure. These variations in density have significant implications for the physical behavior of the lava flow. When sections of lava solidify at different rates or under varying conditions, the resulting contrast between the denser and vesicular materials can lead to directional reorientation during subsequent geological processes. For example, during tectonic movements or erosion, the differences in density can influence how the sections break apart or how they are displaced, potentially leading to the rotation or tilting of the flow layers. This insight is particularly relevant for geologists when interpreting the history and dynamics of volcanic activity, as well as for understanding the potential for reactivation or instability in older lava flows. The uniform density mentioned in one of the alternatives would not provide these contrasting structural features necessary for reorientation, while intrusive rocks and magmatic layering deal more with the interactions of magma beneath the surface