Glacial Milks and Their Laboratory-Simulated Counterparts

Abstract

The dissolved major ions and amount of suspended sediment were determined in five glacial milks from the United States, seven from the Alps, three from Norway, and meltwater from two glaciers in the Antarctic. Highest dissolved silica, 8 ppm Si, was found in Emmons and Nisqually glacial milk, Mt. Rainier, where the country rock is largely andesitic volcanic. Lowest silica, .42 ppm, was determined in glacial milk from granite in Norway. Highest dissolved Ca, 26.6 ppm, and Mg, 7.6 ppm, were determined from Diablerets and Trient (Alps) milk respectively, from limestone terrain, but milk from greenstone, ophiolite, and diabase at Zermatt (Alps) is also high in Ca and Mg. Highest K, 1.72 ppm, was determined from Chamonix (Alps) glacial milk from granitic rock, but K was also high in milk from Mt. Rainier andesite. Highest Na, 3.05 ppm, and P, 1.54 ppm, were found in Emmons and Nisqually milk. Composition of country rock, and the rock9s susceptibility to hydrolysis and solution control the dissolved load of glacial milk. The pH values of all glacial milks were 6.4–7.5 except those from Norway (4.1–4.5). The pH of rock slurries, made by pulverizing under water in the laboratory rocks from the moraines of the glaciers, ranged from 8.2 to 9.8 and correlated with abrasion pH of their constituent minerals. The pH of the slurries ran higher than the pH of corresponding glacial waters. Dissolved constituents in rock slurries were commonly higher in concentration than those in glacial milks: Si was commonly 4–6 times higher; Ca, 2 times; Mg, 2–15 times; K, 20–40 times; and Na, 10–20 times. Concentration of dissolved Si tends to increase with concentration of Na and K, but decreases with Ca and Mg. Factors effective in rock dissolution are rock texture, composition, pH of hydrolysate, and exposure to CO 2 . The amount of suspended matter in glacial melt-water is controlled by the character of the rock eroded, glacial abrasion, and glacial melting. Emmons’ milk carried approximately 7100 ppm solids; Grinnell, Chamonix, and a milk from Norway, approximately 5 ppm. Electron micrographs are presented. Glacial milk is a valuable contributor to sustaining fertility of soil because dissolved elements are immediately available to plants and ion-exchange complexes in the soil, and rock flour releases ions moderately readily because of its high specific surface area.