Task: Question Generation
Input (English): Passage: As early as 1881, industrialists proposed altering the natural channel of the Columbia to improve navigation. Changes to the river over the years have included the construction of jetties at the river's mouth, dredging, and the construction of canals and navigation locks. Today, ocean freighters can travel upriver as far as Portland and Vancouver, and barges can reach as far inland as Lewiston, Idaho.The shifting Columbia Bar makes passage between the river and the Pacific Ocean difficult and dangerous, and numerous rapids along the river hinder navigation. Pacific Graveyard, a 1964 book by James A. Gibbs, describes the many shipwrecks near the mouth of the Columbia. Jetties, first constructed in 1886, extend the river's channel into the ocean. Strong currents and the shifting sandbar remain a threat to ships entering the river and necessitate continuous maintenance of the jetties.
In 1891 the Columbia was dredged to enhance shipping. The channel between the ocean and Portland and Vancouver was deepened from 17 feet (5.2 m) to 25 feet (7.6 m). The Columbian called for the channel to be deepened to 40 feet (12 m) as early as 1905, but that depth was not attained until 1976.Cascade Locks and Canal were first constructed in 1896 around the Cascades Rapids, enabling boats to travel safely through the Columbia River Gorge. The Celilo Canal, bypassing Celilo Falls, opened to river traffic in 1915. In the mid-20th century, the construction of dams along the length of the river submerged the rapids beneath a series of reservoirs. An extensive system of locks allowed ships and barges to pass easily from one reservoir to the next. A navigation channel reaching to Lewiston, Idaho, along the Columbia and Snake rivers, was completed in 1975. Among the main commodities are wheat and other grains, mainly for export. As of 2016, the Columbia ranked third, behind the Mississippi and Paraná rivers, among the world's largest export corridors for grain.The 1980 eruption of Mount St. Helens caused mudslides in the area, which reduced the Columbia's depth by 25 feet (7.6 m) for a 4-mile (6.4 km) stretch, disrupting Portland's economy.
Output (English): What event took place that disrupted Portland's economy in 1980?