Final answer:
An actively eroded cliff will show fresh erosion features, like sharp outlines and gullies, while a non-eroded cliff will have a more weathered, rounded appearance and stable slopes with potential vegetation growth.
Step-by-step explanation:
To contrast the profiles of two high-relief cliffs, one being actively eroded and one that is not, one must consider the visual and geological characteristics resulting from erosion processes. An actively eroded cliff will display features such as fresh rock falls, sharp and rugged outlines, and possibly erosional structures like gullies or notches indicating recent rock removal and transport. The vegetation may be sparse due to the instability of the cliff face. Additionally, such a cliff might exhibit features like undercuts and niches formed by water erosion, as observed in the Tassili n'Ajjer plateau.
In contrast, a cliff that is not actively eroded will generally have a more weathered and rounded appearance, with more stable slopes and vegetation potentially growing on it. Over time, slopes can become gentler, and the presence of soil or vegetation on the cliff face suggests a lack of recent erosive activity. The cliff could also show signs of past erosive processes that have since ceased, such as cross-bedding in sedimentary layers or honeycomb weathering patterns from past sea spray, as seen in Zion National Park.
In comparing geologic history using a cross-section like that of a cliff face, geologists can determine a sequence of events and age of formations, though the perspective is limited to the features present on the exposed section. However, features such as the Great Unconformity in the Grand Canyon can still provide valuable insights into geological history.