The Gulches is an area of volcanic rock that is gashed by many channels that lead downhill from the site of a prehistoric glacier to a river. The channels clearly were cut by running water. It was once accepted as fact that the cutting occurred gradually, as the glacier melted. But one geologist theorized that the channels were cut in a short time by an enormous flood. The channels do show physical evidence of having been formed quickly, but the flood theory was originally rejected because scientists knew of no natural process that could melt so much ice so quickly. Paradoxically, today the scientific community accepts the flood theory even though scientists still do not know of a process that can melt so much ice so quickly. Which one of the following is supported by the information in the passage? ['The physical effects of water on rock vary with the speed with which those effects are produced.', 'Only running water can cause deep channels in volcanic rock.', 'The river did not exist before the channels were cut.', 'Geologists cannot determine the amount of heat required to melt a glacier quickly.']