"Chlamydomonas nivalis" is a green alga which owes its red color to a bright red carotenoid pigment (Astaxanthin). This protects the chloroplast and cell nucleus from strong visible and ultraviolet radiation. The green and red pigments absorb light and heat, which gives the alga liquid water as the snow melts around it. Algal blooms may go 25 cm (10 inches) deep. Since each cell measures 20 to 30 micrometers in diameter, a teaspoon of melted snow contains a million or more cells. The algae build up in 'sun cups', which are shallow depressions in the snow. The carotenoid pigment absorbs heat, which deepens the sun cups, and makes the glaciers and snowbanks melt faster.