Over the course of more than 1km, the Yukon River passes through a narrow gorge with 9-12m walls covered with columns of greyish-red basalt, the appearance of which is due to the cooling of the lava. Here the Yukon still flows rapidly, swirling around Devil's Whirlpool. However, the construction of a hydroelectric dam downstream has eased the flow and reduced navigational hazards. Best seen by taking a cruise.