Reconnaissance of
Kautz Glacier/Van Trump Creek Debris Flows

Reconnaissance of Kautz Glacier/Van Trump Creek Debris Flows
W.E. Scott, C. Driedger, and J.W. Vallance
August 2001

Prior to our aerial reconnaissance, the following occurred:

1. On Monday afternoon, 13 August, National Park Service (NPS) employees observe that water in Van Trump Creek (Figure 1; a tributary of the Nisqually River) changed from clear to muddy brown as a result of high sediment content.

2. At about 8:40 PM Tuesday, 14 August, seismometers detect debris-flow activity. The most intense signal lasts for the first 15 minutes. The signal fluctuates in intensity for the next 4 hours, declining to background level between 1 and 1:30 AM, Tuesday, 15 August. Campers and NPS employees describe loud flows in lower Van Trump Creek and the Nisqually River near Cougar Rock Campground. Nisqually River rises about 2 feet in stage, but is restricted to its active braid plain.

3. Between about 9 and 11 PM NPS and Pierce County and State public-safety agencies communicate information about the size of the event and potential for effects outside of the Park. Rumors and misinformation spread through local communities, in part from the media, and some self-evacuation occurs in the Puyallup River valley on the west side of Mount Rainier where USGS and Pierce County are cooperating to install a lahar-warning system and to pursue a program of outreach and public education.

4. At about 10:00 PM, USGS-CVO is alerted by call to Scientist in Charge's beeper from Washington State Emergency Operations Center.

5. Between 10:15 PM and 2:00 AM, USGS-CVO is in periodic communication with Pierce County Emergency Management, University of Washington Pacific Northwest Seismograph Network, and NPS. The location of the flows in Van Trump Creek is puzzling owing to the small amount of permanent snow and ice in the basin, but we assume that the flows are related to release of meltwater that has accumulated over the past week or more of hot sunny weather.

6. At about 1:30 AM on 15 August, Park Superintendent Jon Jarvis inquires about the prudence of evacuating Cougar Rock Campground and Longmire, both along the Nisqually River, in case there is a flow much larger than the initial surge. USGS advises that in similar events the initial flow is typically the largest and that it is difficult to imagine how such a large flow could form short of an eruption or large landslide. Lack of seismicity other than the signal of debris flows suggests that such events are not likely. NPS does not evacuate facilities, but closes main Park road that crosses Van Trump Creek.

7. USGS scientists Driedger, Vallance, and Scott arrive at Park headquarters about 9:30 AM on August 15, confer with Park officials and Steve Bailey, head of Pierce County Emergency Management. We learn that a new gully running from Kautz Glacier into the west side of Van Trump Creek valley was observed earlier that morning. We infer that this is probably the source water for the debris flows.

Figure 1. Van Trump Creek is the unlabeled tributary of the Nisqually River south of Kautz Glacier. The debris flows of August 2001 originated in an area just northwest of the N of "Nisqually Gl." The Park road mentioned in this report roughly follows Nisqually River from Longmire to Paradise Visitor Center.

Shortly after 11:00 AM, USGS scientists begin a survey of the effects of the Van Trump Creek debris flows in a helicopter supplied by NPS. The flight proceeds as follows.

• Leave Kautz Creek Helipad at 2300 ft and fly up Nisqually River drainage. Note evidence of muddy high water throughout Nisqually drainage and see numerous battered logs along bed of active channel. There is no evidence along this reach that peak flow exceeded bank full. At Longmire, 5 km upstream, we later note that peak water level was 2 ½ feet above present level, well below bankfull.

• At confluence of Nisqually River and its tributary, Van Trump Creek, about 3.5 km upstream of Longmire, we observe that a small debris fan (Figure 2) now covers confluence area and has pushed the Nisqually River against the opposite (left) bank. We head up Van Trump Creek drainage. Near Christine Falls about 1/2 km upstream of the confluence, we observe splattered mud at highway crossing and dust on vegetation. The stream channel is scoured to bedrock (but note that much of this reach was previously in bedrock with scattered alluvium and colluvium), much vegetation is removed along banks, and high mud marks occur about 10 m above the stream bottom. Lower bridge for hiking trail appears undamaged but is plastered with mud.
  
  
  

  Figure 2. View upstream of debris flow deposits (brownish color) of August 14-15, 2001, at confluence of Van Trump Creek and Nisqually River. Note that the new deposits divert the Nisqually River to the valley wall. Photogrpah by J. Vallance, USGS.

  
  
  
  
• Arrive at Comet Falls 2 km upstream of the road crossing, all vegetation near the base of the falls is destroyed and switchbacks in the adjacent trail are covered in muddy debris. Nearby trees are coated with dust.

• Continue upstream above falls, where a steep-walled channel is cut ~2 to 5 m deep into glacio-fluvial fill. Trail bridge in Van Trump Park above Comet Falls is destroyed.

• Between elevation 7200 and 8000 ft a channel about 10 to perhaps as much as 20 m deep is cut through glacial debris and, in places, snow patches. The floor of the channel is locally on bedrock. This is a new channel that is obviously the source of the debris flows. It did not exist previously and was first noted earlier that morning by Park rangers (Figure 3). Periodic undercutting and slumping and continual water saturation cause the channel to widen, deepen, and migrate upslope.
  
  
  

  Figure 3. Channel incised by debris flows in Van Trump Park approximate elevation 6,000 feet. Photograph taken August 15, 2001, by J. Vallance, USGS.

  
  
  
  
• Above 8000 ft, a small stream flows in a shallow channel and over the scarp at the head of the debris-flow source (Figure 4). We estimate the stream discharge is on the order of 1 cubic meter per second.
  
  
  

  Figure 4. Source area of debris flows below point of meltwater diversion. A) Kautz Glacier, B) diversion, and C) source area of debris flows in glacial drift. Photograph taken August 15, 2001, by J. Vallance, USGS.

  
  
  
  
• About 11:25 AM, we see several slumps of glacial debris into the stream that initiates a small debris flow.

• We follow the debris flow downstream for a short distance and then go down to the highway to warn NPS people below of the oncoming hazard. NPS ranger clears bridge of visitors and we return upstream.

• At about 11:30 AM (Figures 5, 6) we observe debris flow pour off Comet Falls (Figure 7) (50 m, with two smaller falls above (Figure 8) and below for total drop of 90 to 100 m)
  
  
  

  Figure 5. South side of Mount Rainier showing A) Kautz Glaciers (upper left), B) meltwater diversion (arrow), C) debris flow source area (appearing as black streak in photo upper right), and D) Comet Falls (lower center). Photo taken approximately 11:30am, August 15, 2001, by C. Driedger, USGS.

  
  
  
  

  Figure 6. Debris Flow spilling over Comet Falls, about 11:30am August 15, 2001, close up view. Photograph by J. Vallance, USGS.

  
  
  
  

  Figure 7. Comet Falls as it normally is, September 1984. Photo by C. Driedger, USGS

  
  
  
  

  Figure 8. "Twin Falls" above Comet Falls. Photo by J. Vallance, USGS, August 15, 2001.

  
  
  
  
• The debris flow diminishes downstream of Comet Falls and becomes muddy streamflow before it reaches road crossing; we report this observation to NPS. Helicopter follows stream above debris-flow source area to elevation between 8800 and 8900 ft at margin of Kautz Glacier. We recognize that the cause of the debris flows is the diversion of water into the Van Trump drainage from the Kautz Glacier through a shallow notch in its left lateral moraine just beyond Wapowety Cleaver. The diversion apparently owes its origin to accelerated melting high on the Kautz Glacier and because of damming by a broken up portion of the Kautz Glacier that has been pushed up on top of the left lateral moraine just down slope of the diversion.

• Return to Kautz Creek Helipad shortly before noon. Dave Uberuaga and Mike Gauthier of NPS leave on similar flight.

The initial and largest debris flows late on 14 August in the Van Trump drainage probably originated by landsliding of glacial debris that had become water saturated. The source of water was a small meltwater stream that originates on the east flank of Kautz Glacier. The stream enters the Van Trump basin through a shallow notch in the lateral moraine just below the end of Wapowety Cleaver. The current spell of hot sunny weather has greatly boosted glacier melting. We don't know when the stream changed course into the Van Trump drainage, but by Monday afternoon, NPS observers noted that Van Trump Creek had become muddy.

Kautz Glacier may be experiencing a rise in surface elevation similar to that of nearby Nisqually Glacier where measurements at elevation 1,830 meters show a ten-meter rise in surface elevation between 1998 and 1999. Such an increase in elevation of Kautz Glacier may have created conditions favorable for diversion of meltwater into the drainage of Van Trump Creek.

Future slumping of channel walls will initiate small debris flows as long as sufficient water flows through the channel. We expect this process to be more active during periods of hot weather. Intense rainfall during fall and early winter could generate additional debris flows, some of which could be larger than those occurring now. If the debris flows remain small we expect them to dissipate in the region below Comet Falls. Larger flows could reach the Nisqually River. The Nisqually River will have a muddy appearance as long as debris flows occur.

Debris flows similar in scale similar to those of August in Van Trump Creek occur chiefly in late summer in valleys that head on Mount Rainier's glaciers, owing to glacial outburst floods and intense rainfall that disrupts glacier termini (Walder and Driedger, 1994). In the recent past, debris flows having these origins have begun near the Tahoma, Kautz, and Winthrop Glacier termini. The Van Trump debris flows were a surprise because there is little permanent snow and ice in the basin. The diversion of meltwater from the margin of Kautz Glacier at 8800 feet into the basin provided the water necessary to trigger the debris flows.

The debris flows of August 2001, although of modest size, remind us that the geologic record at Mount Rainier indicates debris flows or lahars of much greater magnitude. Large landslides triggered by intrusion of magma into the volcano, and subsequent failure of locally weakened rock masses, or catastrophic melting of snow and ice by various eruptive processes caused these large lahars (Scott et al., 1995). In the past, lahars swept tens of miles down valleys, and some reached Puget Sound. Scientists continue to work with public officials to develop mitigation plans for coping with future large lahars from Mount Rainier.

References:

Walder, J.S., and Driedger, C.L., 1994, Geomorphic change caused by outburst floods and debris flows at Mount Rainier, WA: U.S. Geological Survey Water Resources Investigation Open-File Report 93-4093, 93 p..

Walder, J.S., and Driedger, C.L., 1994, Frequent outburst floods from South Tahoma Glacier, Mount Rainier, USA: Relation to debris flow, meteorological origin and implications for subglacial hydrology: Journal of Glaciology, vol. 41, no. 137, pp. 1-10.

Scott, K.M., Vallance, J.W., and Pringle, P.T., 1995, Sedimentology, behavior and hazards of debris flows at Mount Rainier, Washington: U.S. Geological Survey Professional Paper 1547, 56 p.