Lava Canyon Bridge, 1993 & 1999 Mt. St. Helens National Volcanic Monument, WA

Satellite view of Bridge. View Larger Map

USE:  Pedestrian

SPAN:  100'

TRAVEL WIDTH :  3'

TOWERS:  17' tall, Penta treated #1 Douglas Fir

ANCHORS:  30' long by 1-3/8" Rock Bolt each mainline

MAINLINES:  1-1/8", Stainless Steel, 6x19 Wire Rope

The Lava Canyon Suspension Bridge is located on Mt. St. Helens National Volcanic Monument in Washington State. It is the primary link across Lava Canyon for a 1.5 mile interpretive trail constructed in the aftermath of the Mt. St. Helens eruption of 1980. This bouncy, lively bridge is precipitously located just above the Lava Canyon Falls, the thunder of which mutes the voices of the bus loads of tourists and school kids that visit the site on a daily basis.

This bridge is one of Sahale's earliest cable bridges and was constructed under contract to the U.S. Forest Service using an agency-supplied design. It is a very dynamic and light pedestrian suspension bridge utilizing treated timber towers, rock anchors, and lacking any stiffening members such as floor beams or stringers below the deck. Instead, the deck rests upon horizontal under-deck cables running longitudinally from one tower abutment to the other. This latter characteristic is the bridge's most unique feature and imparts a trampoline-like feel when it is crossed.

Access to the site is challenging, as the bridge is located deep in the canyon, at the end of a rather precipitous and dangerous trail, hundreds of feet lower in elevation than the trailhead. To stage materials and construction equipment to the site, Sahale used a Madill 071 Yarder, placing it in an old logging cut and erecting a skyline across the canyon to a tailhold anchor more than 2,000 feet away. Air compressor, air track drill, and the bulk of bridge materials were sent down the skyline to the site. Even the towers were pre-assembled at the old log landing, and delivered in one piece to the bridge site via skyline, then tilted into position. Assembly of the mainspan was accomplished using a much smaller skyline over the canyon.

The photos on this page show two views of the bridge nearing completion in 1993. In 1999, Sahale was retained by the U.S. Forest Service to provide an inspection, adjustment, and maintenance services for the Lava Canyon Bridge, and to develop and implement engineering upgrades to the railing and fence system.