of the most studied glaciers in North America. The glaciers of the park have been dramatically reduced in size in the late 20th and early 21st centuries. Precise measurements of glacial areas started with the Vaux family and A.O. Wheeler in the 1900s. Modern measurements using satellite imagery began with Simon Ommaney's work in the 1980s. Regular inventories of the park’s glaciers have been performed since, with the latest collating data up to 2011. The most recent inventory noted a reduction of of glacial surface area from 2000 to 2011. Due to its location near the highway and railway, the Illecillewaet Glacier is the most visited and photographed. Formerly known as the Great Glacier, it was a major tourist attraction during the Glacier House period from 1886 to 1925. The glacier's terminus, formerly a short walk from the Glacier House site, has retreated far up the mountainside. The névé of the glacier spreads far to the south, also spawning the Geikie Glacier. Most of the large glacial features are south of the Trans-Canada corridor. Other large features include the Deville, Dawson, Asulkan, Bishops, Black, Duncan, Grand, and Avalanche. The park's glaciers have a variety of appearances, with high altitude features smooth and uniform, cracked and riddled with crevasses on the slopes, and black with debris on the valley bottoms. In summer, many of the glaciers take on a red tint; this is the result of a variety of snow algae known as watermelon snow. Rivers All watercourses in the park are part of the Columbia River drainage basin. Park rivers are swift-running and glacially-fed, and have helped carve out the steep valleys and canyons. They carry much silt and rocky debris with them, and often have a milky white appearance. In the summer months, these rivers have noticeable diurnal cycles; they run high in the afternoons as the snow and ice melt is at its peak, then drop considerably with lower nighttime temperatures. The major rivers are the Illecillewaet, the Beaver, and the headwaters of the Incomappleux and Duncan Rivers. Large creeks and brooks include Mountain, Cougar (which runs underground through the Nakimu Caves), and Battle. The Beaver and Illecillewaet flood occasionally; 1983 and 2012 saw flooding damage to the highway and railway. Geology The geology of the northern Selkirks reveals the tremendous tectonic changes that have shaped the terrain of western North America. Like much of British Columbia, the