The avalanche late Wednesday smashed into a freight train about 15 miles south of Portage. The snow buried at least 10 of the train's 64 cars and threw some off the tracks, said railroad spokesman Tim Thompson.
The train was hauling lumber, wallboard and other building materials from Seward to Anchorage.
Railroad crews must secure the area against more avalanches before they can begin digging out the trains and assessing the damage, Thompson said.
The area, which is in a mountain pass accessible only by rail, is known to be prone to slides, he said.
Another avalanche Thursday afternoon temporarily closed the Whittier tunnel when railroad crews working on avalanche mitigation triggered a fall.
"There was just a large amount that moved down," Thompson.
No one was injured.
That avalanche, at Mile 5.5 of the Portage Valley Road, piled 14 feet of snow over 50 to 75 feet of road.
Important warning about e-mails purporting to be from the adn.com staff.