One group of debris flows came down Leaven's creek, a small creek that flows from the basin between Yeon Mountain (left side of above photograph) and Saint Peters Dome (right side). The creek collects water from this basin and from the plateau above, from where it cascades in waterfalls into the basin. The creek flowed between the residence of Carol and Hersh Royse and Carol's sisters' house to the west. When this creek was blocked by debris, subsequent flows were diverted straight towards their house (above, see also a 1:250 scale map of the Royse Debris flow deposit).

• Description of the debris flow event
• Map of debris flow deposits
• Aerial photograph and images of the source area
• Aerial photograph and images of the deposit
• Weather conditions at time of flows
• Photographs for 2001 Flow (just to East of 1996 flow)

Carol Royse perhaps best tells their story:

On Feb 8th we awakened to mud around our house and deep ruts in the driveway. But it was calm. The only ones on the freeway were the workers trying to clean the other slides away [the freeway had been blocked by large debris flows from Tumalt creek the night before]. Hersh got to go to Gresham to get pipe to fix the water line [The water line runs from a spring near Saint Peters Dome and was broken by floodwaters on 6th February where it crossed Leaven's creek]. He left in the 4x4 truck about 10:00 AM.

I put on my boots and went outside to see how much damage the mud and water caused the night before. It had stopped raining temporally. I remember walking by one of my flower beds in the backyard and seeing some of my daffodil bulbs exposed by the water, thinking to myself "I’ll have to get a shovel and cover them up" … little did I know.

I went back into the house and watched my pet Raven playing on the dresser challenging her image in the mirror that hung on the wall above the dresser. She was so much fun. About noon Hersh came home with the pipe and some gas for the generator. He left the truck down by the service road because of the ruts in the driveway from the night before. Hersh hooked up the generator to the little TV in the dining room so we could watch the news. About 12:30 I heard something. The generator noise made it difficult to determine what I was hearing. I looked out the front door and saw the horses looking towards the mountain. They were scared. I felt a vibration – I told Hersh "Something was wrong". I went to look out the back kitchen window. What I saw sent chills down my back.

I saw a huge wall of mud, water, rocks and trees coming right at us. It was already half way down the back field. I said "We’ve got to get out of here!!" Hersh said "Wait a minute" and went to see of himself. When he saw what I was talking about he said "Let’s get the hell out of here!!"

At that point we ran out the front sliding doors that led to the front porch. I heard the doors slam shut behind us unknowingly trapping my bird and our dog, Moe, inside. We ran straight down from our house, crawled through the board fence and straight down through the field to the road. Halfway I turned to see the garage and small motor home shed go down like a cracker box. It was engulfing the house. A big fir tree rolled around the front of the house. When we reached the fence at the bottom of the field the horses were with us. As we fought to get the gate open to let the horses out, they turned and ran back up to the barn and right into the sliding debris. Our mare – Bugsy went down, we thought she was lost. Hersh went backup to try to get them out, against the opposition from my brother Joey and nephew Todd, who were very concerned for his safety. Being the stubborn man that he is he went anyway. After reaching the horses he gave the mare a hand signal. She struggled and finally got up. Cisco my youngest daughters' pinto horse followed the mare out. Joey led the horses to safety while Hersh made his way back to the house to save Moe [our dog] who got locked in the house. Poor Moe was standing on his hind legs against the glass doors with just his head sticking out of the mud that now filed the house up to the drain boards. Hersh had to break the glass doors with a brick that he found on the front porch to get Moe out. He then made his way into the house to get his billfold & asthma medication, wading in 3 to 4 feet of mud, boulders & water. His boots were filled with mud and rocks which made it difficult to get around.

Hersh and I stood with the others [while the mud and debris] slowly surround our home and property. About 4:00 O’clock it was still coming down and swallowing up the green pastures. When we left for town I was still crying as we pulled out onto the freeway. The house was still showing, as was the fence when we left. We had no idea what we were going to do.

On Feb 9th around noon we returned to retrieve what we could. When we got here I was not prepared for what I saw. I could not believe what I saw. There was from 4 to 15 feet of mud, boulders and trees completely covering our property. The house was a disaster. The whole West side of the house was torn open. The fireplace and everything in the living room was gone. My piano and furniture were out in the fields. There were belongings and pictures floating in the mud clear out to the freeway. The front porch was gone. Our home was no more.

Summary

The Royse debris flows were initiated by runoff from four consecutive days of record rainfall (32 cm in 4 days) combined with melting of the snowpack at higher elevations. The runoff was concentrated in Leavens Creek. In the upper and middle portions of the creek the runoff picked up mud and boulders from the channel and produced a series of debris flows.

Velocities of the debris, as estimated from tree-runup, are in the order of 6 m/s where the flow was confined to a single channel, and about 4-5 m/s where the flow was moving thorough the forest above the Royse House. A velocity of 5.1 m/s was obtained from channel tilt at a curve in the easternmost channel. These are similar to velocities obtained for flows that came down Tumalt Creek 1 km to the east.

The preserved deposits have a volume of 22,000 to 25,000 m³. This volume of material could easily have been generated by channel deepening. A 220-250 m length of channel 20 m wide deepened by 5 m would generate the volume needed. The channel is deeply incised for about 1 km.

The last debris flow left a lobe that is about 1m thick, and has a surface slope of 5°. This gives a Bingham strength of 2.5 × 10⁴ dn/cm to 3.2 × 10⁴ for densities ranging from 2.0 to 2.5 g/cm³.

References

Briggs, K., 1996. Gorge Geology raises the stakes. The Oregonian, August 20 1991, p. 1

Cruikshank, K.M. 1997. The Royse Debris Flow, Dodson, Oregon. Geological Society of America Abstracts with Programs. 29.

Cruikshank, K.M. 1997. Dodson Debris Flows, Oregon. Association of Engineering Geologists. Program with Abstracts for 1997 Annual Meeting, Portland, Oregon, p. 93.

Johnson, S.E., 1997. 1996 Tumalt debris flow and debris avalanches in Columbia River Gorge east of Portland, Oregon. 1st International Conference on debris-flow hazards and mitigation: Mechanics, predication and assessment. 7-9 August 1997, Hyatt Regency, Dan Francisco, California.

Powell, W.O., Robertson, C.A., and Watanabe, R.F., 1996. Geotechnical report, Dodson.Warrendale debris flows. Columbia River Highway, #2 MP 34.5 to 37.5, Multnomah County. Oregon Department of Transportation, Portland, Oregon. 11 p.