Glaciers were formed on land over many years, often centuries. They have carved out valleys and sculpted mountains. Glacial ice is very dense and blue.
Your ship will get up close to the glaciers in Glacier Bay National Park or Tracy Arm most likely. You might see Hubbard Glacier (depending on your itinerary) which is the largest tidewater glacier in N. America at 76 miles long and 7 miles wide.
When your ship gets close to the glaciers go out on your balcony or on the upper deck and be very quiet. If you listen you will hear them crack and break off. This is called "calving".
Your ship will have a stop in Juneau. Hop on a bus and take the 10 minute ride to Mendenhall Glacier. It is worth seeing. There is a park ranger on duty to answer your questions.
If you want to actually walk on a glacier take a helicopter ride which will land on a glacier. It's a thrilling experience!
I will be glad to help you plan your Alaska cruise and tours for next summer. I will find you the best ship and best cabin at the best price. Give me a call at 336-922-1837.