Remobilization of Ash by Wind

Following ashfalls the unconsolidated ash deposit is susceptible to wind erosion, transport and eventual deposition. This is can be a severe problem in dry, windy areas. Recent ashfalls in Iceland and Chile have created considerable problems for exposed communities from ongoing wind remobilization of ash deposits. For example, some farms in southern Chile after the 1991 Volcán Hudson eruption could not return to operation due to constant ash remobilization from wind within the region. This prevented whole communities returning to their properties for months and in some cases even years.

Novarupta-Katmai Ash Resuspension

Resuspension and transport of fine-grained volcanic ash from the Katmai National Park and Preserve region of Alaska have been observed and documented over the past several decades, but has likely been occurring ever since the 1912 Novarupta-Katmai eruption. This eruption produced approximately 17 cubic kilometers (4 cubic miles) of ash deposits and 11 cubic kilometers (2.6 cubic miles) of pyroclastic flow deposits that filled nearby valleys, creating what is today known as the Valley of Ten Thousand Smokes. Filled with up to 200 meters (660 feet) of ash and pyroclastic material, the valley remains almost entirely free of vegetation.

During the spring and fall, when strong northwesterly winds blow over the snow-free landscape, the ash can be picked up (reworked) into dust clouds. The ash is especially susceptible to reworking when the ground has been dry for extended periods. These dust clouds have been observed both visually and in satellite imagery. Documented dust clouds have been estimated to be between 1 and 3 kilometers (4,000 and 11,000 feet) above sea level and seen to extend up to 250 kilometers (155 miles) over Shelikof Strait, parts of Kodiak Island, and over the Gulf of Alaska. Trace amounts of ash fallout (typically less than 1 mm or 1/32 inch) have been reported on communities on Kodiak Island and samples have been found to be primarily composed of volcanic ash.