A large boulder carried by a glacier and left behind on bedrock of a different type when the ice melted is called
Answer: A
Correct answer: An erratic
A glacial erratic is a rock transported by ice and dropped far from its source, and it is recognised precisely because it does not match the bedrock it sits on. Erratics were among the first pieces of evidence for the ice ages: geologists in the nineteenth century could not explain granite boulders resting on limestone hundreds of kilometres from any granite, until glaciers were proposed as the carrier. Tracing an erratic back to its parent outcrop reveals the direction the ice flowed. The other three are also glacial landforms, but each is a shaped deposit rather than a single stray rock. A drumlin is a streamlined hill of till moulded beneath the ice; an esker is a long sinuous ridge of sand and gravel laid down by a stream flowing within or under the glacier; and a kame is a mound of debris dropped where meltwater ponded against the ice.
Please log in or register to report this question.