As Owen and Smyser note, this passage almost certainly alludes to J.M.W. Turner (1775-1851), who painted a series of Alpine landscapes after returning to England from Switzerland in 1802. Wordsworth might also have been thinking of Philip James de Loutherbourg (1740-1812), the German-born but London-based painter of Avalanche in the Alps (1803). Illustration: De Loutherbourg’s Avalanche in the Alps (Wikimedia Commons).