The massif contains 11 main summits over in altitude, as well as numerous subsidiary points above this height.: Crowning the massif is Mont Blanc (), the highest mountain in the Alps and in western Europe.: From the summit of Mont Blanc to the Arve near Chamonix there is a drop in altitude over a distance of just .: Because of its great elevation, much of the massif is snow- and ice-covered, and has been deeply dissected by glaciers. The Mer de Glace is the longest glacier in the range as well as the longest in France and the second longest in the Alps.:: The debris-covered Miage Glacier on the southern side of the massif is the longest in Italy.: