Final answer:
Extrusive igneous features such as pahoehoe, a'a, pillow basalt, and columnar basalt each reflect unique conditions and appearances of basaltic lava upon eruption and cooling, with specific terms used to describe their distinct characteristics.
Step-by-step explanation:
The best term to describe an extrusive igneous feature such as pahoehoe, a'a, pillow basalt, or columnar basalt is highly dependent on the specific characteristics of the lava flow.
For example, pahoehoe is smooth and billowy or ropy and is often associated with fast-flowing, hot basaltic lava. A'a refers to basaltic lava that solidifies with a rough, jagged, and clinkery surface. Pillow basalt is typically found underwater and forms when lava erupts under sea or lake water, creating rounded, pillow-shaped structures.
Columnar basalt is characterized by its column-like structure, which results from contraction as the lava cools. The various terms reflect different conditions under which the lava has erupted and cooled.