English: On November 18, 2017, the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite acquired a true-color image of dust blowing out of the Copper River Valley. The dust poured down the valley and widened as it blew over the river delta on Alaska’s south coast. The airborne dust plume stretched hundreds of kilometers across the Gulf of Mexico. The dust plume was likely comprised of fine-grained loess, which was formed as glacial ice moved over the area and ground the underlying rock into a powder (sometimes called “glacial flour”). Dust storms in southern Alaska generally occur in late fall, when river levels are relatively low, snow has not yet fallen, and the layers of dried, loess-rich mud are exposed to the wind.