Final answer:
Glacial retreat is characterized by the melting and shrinking of the glacier's extent, which occurs when the glacier's melting rate outpaces its accumulation of snow and ice.
Step-by-step explanation:
During a glacial retreat, the correct process that takes place is d) Melting and shrinking of the glacier's extent. Glacial retreat happens when the glacier's melting rate exceeds the accumulation of snow and ice. As a result of this process, the glacier's terminus, or end point, moves backward over time, leading to a reduction in the overall size of the glacier. This is indicative of the changes in the physical environment associated with climate change, with observable reductions in glacier mass in places like Glacier National Park in Montana and in ice sheets in Greenland and the Antarctic.
It's important to note that while processes such as abrasion and plucking of bedrock by glacial ice do occur during a glacier's lifetime, they do not specifically describe a glacial retreat. Similarly, the advance of the glacier over the landscape refers to its movement outward, not retreat.