3-D perspective of bare-earth lidar data looking east towards Green Ridge with the Mile 29 Debris Flow on the left and Lower Bridge on the right click to expand
Geo-Exploration: Head of the Metolius & Mile 29 Debris Flow
Led by Bob Timmer & Bob Jensen
October 18, 9:15 AM - 4:00 PM
Registration opens October 11th; limited to 20 participants
This field trip will have two components, first a stop at the Head of the Metolius and then a 1-mile hike (2 miles round trip) along the Metolius to examine the Mile 29 Debris Flow.
Trip Itinerary
Meet at Cascade Village Mall between PetSmart & Ashley Furniture @9:15AM to check-in and, optionally carpool.
Depart Bend @ 9:30AM from Cascade Village Mall
Drive west on Highway 20, through Sisters, past Black Butte, and turn right on the Camp Sherman/ Metolius River Road. Continue north for 2 1/2 miles to a "Y" and proceed right on Forest Service 14. Continue ~2 miles on FS 14 to the Head of the Metolius turn on the left. Proceed to the parking area. Restroom facilities
Stop 1 - Head of the Metolius
We will walk 1/4 mile to the headwaters spring where the Metolius River emerges at the base of Black Butte. James et al. (2000) included the Metolius River headwaters spring in their analysis of groundwater flow in the Deschutes Basin using temperature, stable isotopes, and noble gases. This analysis showed that groundwater discharging at the Metolius headwater spring not only picks up geothermal heat along its flow path, but magmatic volatiles as well. Estimates of the age of the water varies from 47 to 120 years. The headwater spring was known for a relatively constant discharge of 100-125 cfs (Peterson & Groh, 1972). In August 2021, the Bend Bulletin reported, “In June 2018, the head of the Metolius had an outflow of 102 cfs. That dropped to 95.6 cfs in June 2019, 74 cfs in June 2020 and 55 cfs in August 2021”. Flow in September 2023 was reported at 47.9 cfs. Flow in the Metolius increases dramatically with input from springs and tributaries.
Return to cars and return to FS 14. Turn left and proceed to north on FS 14 for ~9 miles to the parking area on the east side of the Metolius at Lower Bridge.
Stop 2 - Lower Bridge parking area & hike to Mile 29 Debris Flow
We will hike 3/4 mile downstream from the Lower Bridge Campground to a spot along the river for lunch. We will be hiking along a single-track, lightly maintained trail with small elevation changes. After lunch, we will hike another 1/4 mile on an unmaintained trail to the toe of the Mile 29 Debris Flow.
Bare-earth lidar data of Mile 29 Debris Flow - click to enlarge
THE MILE 29 DEBRIS FLOW -- WHAT HAPPENED?
Larry Chitwood and Bob Jensen, Geologists
Deschutes National Forest
April 10, 1996
At the height of the February Flood of 1996, a torrent of water and debris careened 3400 feet down a small canyon on Green Ridge. From the mouth of the canyon, an estimated 600,000 cubic feet (22,000 cubic yards) of debris-laden water shot across a gently-sloped, forested, alluvial fan at about 30 miles per hour. In thirty seconds the torrent reached the Metolius River at Mile 29 leaving in its wake a stark eight-acre field of boulders. About a dozen large trees survived the onslaught. Up to eight vertical feet of bark were battered away by rocks, and mud surged up the trunks leaving stains as high as 25 feet above the ground............
There is more to the story.......which we will hear from Bob Jensen
After examination of the toe, we will continue our view of the debris flow by walking cross-country along the southern margin of the flow to Forest Service road 1499. We will then return to our vehicles with a 1-mile hike along FS 1499 to Lower Bridge.
Stop 3 - Down Canyon Viewpoint on FS 1490
From Lower Bridge, retrace drive on FS 14 about 1/4 mile to FS 1490 on the left. Drive 2 miles up FS 1490 to "down canyon viewpoint". It is nearly impossible to appreciate the gradient of this canyon, and western slope of Green Ridge, until you stand at this viewpoint and look down the canyon.
Stop 4 - optional stop panoramic view across the basin
Depending on time and weather, to drive a further mile up FS 1490 for a panoramic view
Return to Bend at 4:00PM
Notes:
- Please note that the weather is changing and getting COOLER
- Please wear appropriate footwear for the hike, appropriate clothing and consider bringing hiking poles
- It is hunting season; the risk should be low due to the noise we will likely be making on the trail.
- Bring a sack lunch and water
- Please leave your dogs at home
- Pit toilets are available at Metolius Headwaters and Lower Bridge Campground
