Glacier ice is hard, but definitely not hard enough to carve rock. Then how do they carve out valleys? The answer lies at the bottom of them. As the glaciers slip and slide down the hill friction causes a thin layer of water to form. To understand what happens next, imagine a time you reached into a freezer with wet hands to grab some ice. What happened? The ice stuck to your hand right! The same concept happens with these glaciers. A sandpaper like skin is created because this same freezing bond causes gravel and rock to latch to the bottom of the glacier. Therefore, glaciers act like wood workers smoothing out the valleys leaving behind a distinct look.
While on your small ship cruise in Alaska, I encourage you to see if you can spot a glacier carved valley. Glaciers tend to carve out a unique U shaped valley with steep sides and a broad open valley floor. To help spot these, use your hands as view finders: Using your thumb and pointer finger make L like shapes with each of your hands allowing the thumbs to touch.
You might also notice valleys that tend to be more V shaped. These are typically carved out by different types of running water (waterfalls, runoff, streams, etc.). To spot these, you can use the international peace sign as your personal view finder.
If you’d like to learn more, visit https://www.nature.nps.gov/geology/usgsnps/glacier/uvalley.html the National Park Services USGS description of how valleys are formed.