Science Olympiad Dynamic Planet Practice Test

Which type of lava has a smooth, rope-like, swirled surface?

1. aa

2. pahoehoe

3. mafic

4. obsidian

The correct answer is: pahoehoe

The type of lava characterized by a smooth, rope-like, swirled surface is pahoehoe. This type of lava flow has a much lower viscosity than aa lava, allowing it to flow more easily and create the distinctive, billowy, and often glossy surface texture. The smoothness and ropy appearance are due to the way pahoehoe forms as it slowly cools, maintaining its fluid state longer and allowing for these unique surface patterns to develop. Pahoehoe can generally flow at higher temperatures and offers clues about its composition, typically being basaltic. This results in a less fragmented surface compared to other configurations, presenting a visually smooth appearance. The formation of these surface features is indicative of the rheological properties of the lava as it moves and cools. In contrast, aa lava is rough and jagged, formed when it cools and solidifies more quickly, thus presenting a sharp and blocky surface. The other options, mafic and obsidian, refer to different aspects of volcanic materials rather than specific textures of lava flows. Mafic is a term that describes the chemical composition of the lava, while obsidian is a volcanic glass formed through rapid cooling of lava, lacking a typical lava flow surface altogether.