U.S. Department of the Interior

U.S. Geological Survey

DEBRIS FLOWS–GEOLOGIC PROCESS AND HAZARD

ILLUSTRATED BY A SURGE SEQUENCE AT JIANGJIA RAVINE, 

YUNNAN, CHINA

Professional Paper 1671
COVER PHOTOGRAPH

Head of alluvial fan of Jiangjia Ravine. Rice fields on the deposits of debris flows (occurring 

in the 1980’s). Photo by K.M. Scott.
DEBRIS FLOWS—GEOLOGIC PROCESS AND HAZARD

ILLUSTRATED BY A SURGE SEQUENCE AT JIANGJIA RAVINE, 

YUNNAN, CHINA

By Kevin M. Scott and Wang Yuyi

A study and video recording of debris flows at Jiangjia Ravine in 

Yunnan Province, China. This rugged and remote site is famous

for the annual occurrence of debris flows that present serious

risks to those living in this mountainous region.

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1671
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Government

Reston, Virginia

For sale by U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Scott, Kevin M., 1935-

 Debris flows: geologic process and hazard, illustrated by a surge sequence at Jiangjia Ravine, Yunnan, China/

by Kevin M. Scott and Wang Yuyi

 p. cm. -- (U.S. Geological Survey professional paper; 1671)

Includes bibliographical references and index.

1. Debris avalanches--China--Yunnan Sheng. I. Yuyi, Wang, 1941 - II. Title. III. Series.

QE599.C6S36 2004

551.3’07’095135--dc22

2004047101
CONTENTS

Abstract ..............� 1

Introduction–why study debris flows? ................................................................................................ 1

 Debris flows in Southwest China .................................................................................................. 4

 The great rivers of China and erosion of the landscape ................................................................. 6

What can we learn from the video? ..................................................................................................... 6

 Flows of water and sediment comprise a spectrum of increasing sediment content from

 floods, to hyperconcentrated flows, to debris flows ................................................................... 6

 Debris flows can move huge boulders ........................................................................................... 8

 Forming rivers of rock ................................................................................................................... 8

 Debris flows are faster than flood waves ........................................................................................ 8

 Flow geometry—depth and width—and channel slope ................................................................. 10

 How much sediment is moved by individual surges and by complete series? ................................. 10

 Why debris flows can crush man-made structures–powerful impact forces .................................... 10

 Like wet cement ............................................................................................................................ 10

 Why multiple surges? .................................................................................................................... 11

 Ballistic clast ejection–estimating flow velocity from runup height ................................................ 11

 Estimating cross sections of debris flows ....................................................................................... 11

 Knickpoints ..� 12

 How and why we seek to identify deposits of old debris flows ....................................................... 12

 Can people be warned that a debris flow is coming? ...................................................................... 14

 Mitigation and countermeasures ................................................................................................... 17

Acknowledgments .............................................................................................................................. 17

References cited, and for further study ............................................................................................... 18

FIGURES

 1. Index map showing location of Jiangjia Ravine ........................................................................ 2

 2. Photo showing video site in Jiangjia Ravine ............................................................................. 3

 3. Photo of surge front on June 15, 1990 ..................................................................................... 5

 4. Photo of debris flow deposits in Jiangjia Ravine, showing debris cones on valley-side 

 slopes formed by mass flow ................................................................................................... 9 

 5. Photo of debris flow in channel, incorporating mass of material. .............................................. 9

 6. Photo of longitudinal roll waves and concave surface of right-to-left flow in bend 

 on June 15, 1990 .................................................................................................................. 12
 7. Diagrammatic cross-sections of flow illustrating differences in cross-sectional area 

 (and thus, discharge) as they depend on reconstruction of the flow surface

 from deposits ........................................................................................................................ 13

 8. Texture (particle size distribution) of debris flow deposits, as histograms .................................. 15

 9. Data in figure 8 plotted as cumulative curves ........................................................................... 16

 10. Photo of cutbank showing debris flow deposits over those of flood or

 hyperconcentrated flow ......................................................................................................... 16

 11. Photo of downstream reach of Jiangjia Ravine .......................................................................... 17

TABLES

 1. Annual sediment yields of debris flows in Jiangjia Ravine ......................................................... 4

 2. Data for surges seen in video/DVD .......................................................................................... 7

APPENDIX

 Narration ......� 23

 

CONVERSION FACTORS

Multiply By Obtain

millimeters (mm) 0.03937 inches (in.)

centimeters (cm) 0.3937 inches (in.)

meters (m) 3.281 feet (ft)

cubic meters (m3) 0.028 cubic feet (ft3)

kilometers (km) 0.6214 miles (mi)

square kilometers (km2) 0.3861 square miles (mi2)

meters per second (m/s) 3.281 feet per second (ft/s)

meters per second (m/s) 2.237 miles per hour (mph)

kilometers per minute (km/m) 37.28 miles per hour (mph)

cubic meters per second (m3/s) 35.31 cubic feet per second (cfs or ft3/s)

hectare–10,000 m2 (ha) 0.405 acres–43,560 ft2 (ac)

 

iv Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China
Debris Flows–Geologic Process and Hazard

Illustrated by a Surge Sequence at Jiangjia 

Ravine, Yunnan, China

By Kevin M. Scott and Wang Yuyi1

ABSTRACT

 Debris flows are slurries of sediment and 

water that are both an important geologic process 

and a major hazard. They present large risks 

to those living in mountainous areas, as well as 

downstream from volcanoes in the case of the 

flows known as lahars that may travel 100–200 

kilometers (62-124 miles). The accompanying 

video records a series of debris flow surges at 

Jiangjia Ravine, in Yunnan Province in southern 

China. This rugged and remote site is famous for 

the annual occurrence of debris flows triggered 

each summer by monsoonal rains. The video 

illustrates the unique characteristics of debris 

flows, how they behave, and why they cause 

large losses of life and property in China and 

many other parts of the world. This report is a 

summary for those wishing more information 

than is presented in the video, and for the 

specialist we include dynamical data on the flows 

and textural data on their deposits. 

INTRODUCTION – WHY STUDY DEBRIS 

FLOWS? 

 The Chinese Academy of Science studies the 

recurring debris flows at Jiangjia Ravine (fig. 1) 

in order to define their origin and behavior and 

thereby find ways to reduce the risks of debris 

flows to life and property (Kang, 1989; Cui, 

1992; Du and others, 1995). Huge sediment 

yields—volumes of sediment discharge per 

unit area—are moved by debris flows. These 

high sediment yields can markedly reduce the 

capacity of downstream flood-control and powergenerating facilities. Among these is the Three 

Gorges Dam, the world’s largest dam scheduled 

for completion on the Yangtze River about 

2010, located approximately 1,000 km (620 mi) 

downstream from Jiangjia Ravine. We use metric 

units throughout our discussion, with their 

customary (“inch-pound”) equivalents for some 

measures of distance, velocity, and volume.

1

Institute of Mountain Hazards and Environment, Chengdu, China
2 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

Y na g zt e

River

River

Jinsha

Mekong River

120o

103oo10'

45o30o15o

26o20'26o10'

105o 90o 75o

30o

30o

105o

110o

100o

25o

YUNNAN

SICHUAN

Kunming Observation site

0 2 Kilometers

500 Miles 0 

500 Kilometers 0 

R ahs niJ

vi er

Xiaojiang River

Jiangia

Ravine

JIANGJIA RAVINE

Chengdu

Dadu River

500 Miles 0 

500 Kilometers 0 

Jialing River

Fu Ri v er

Min River

Min River

Tuo River

ALP ET UA

FRONT

ALP ET UA

FRONT

Qinghai-Tibet

Plateau

revi Rgnaij oai X

Kunming

Chengdu Wuhan

BEIJING

Nanning

Guangzhou

South China Sea

Figure 1. Index map showing location of Jiangjia Ravine.
 Mountains comprise 33 percent of China’s 

land area of 9.6 million km2 (3.7 million mi2). 

Jiangjia Gou (Ravine or Gulley) is one of 

approximately 50,000 small mountain 

watersheds called “sediment highways” that yield 

debris flows in China (Ou, 1999). Ravine or 

gulley, the best translations of gou, are overly 

diminutive, but there is no really analogous 

term in English. The drainage area (figs. 1 and 

2) is 48.6 km2 (19 mi2), and the main channel 

is 13.9 km (8.6 mi) in length. Relief is from 

1042 to 3269 m.a.s.l. (3,419 to 10,722 ft). The 

sparse rainfall, with 85 percent concentrated in 

monsoonal storms from May to October, has 

ranged from 307 to 886 mm/yr (12.1 to 34.9 in/

yr) in recent years (table 1). Consequently, 

vegetation has not recovered from long-term 

deforestation, and erosion rates are high. Nearly 

all the sediment discharge from the drainage 

occurs as what can be described as episodic 

“express trains” of debris flow (Cui, 1999). In 

spite of the harsh environment, many small 

villages survive tenaciously throughout the basin, 

subsisting on rice grown on the debris flow 

deposits in the main channel (the only green areas 

in the video), and on other crops from upland 

areas. Most intermediate altitudes are too steep 

for humans or domestic animals.

 The flows at Jiangjia Ravine (fig. 3) are very 

similar in their behavior and physical properties 

to their huge analogs, lahars, that occur in 

volcanic terrains and from volcanoes. Although 

the Peoples Republic of China has few volcanoes 

of the type that produce lahars, elsewhere around 

the circum-Pacific “Rim of Fire” lahars have 

taken many thousands of lives in recent decades. 

Case histories of catastrophic examples, with 

recommended mitigation strategies, are described 

by Scott and others (2001).

Figure 2. Photo showing video site (arrow) in Jiangjia Ravine and location of the Dongchuan Debris Flow Research and 

Observation Station (DDFROS). Note rice field development on recent debris flow deposits, upper left. Photo by R.J. 

Janda.

Introduction – Why Study Debris Flows? 3 
4 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

Debris Flows in Southwest China

 Debris flows are a widespread means of 

sediment transport in the mountainous and 

semiarid parts of Southwest China (Du and 

others, 1995; Ou, 1999). In recent years, the 

annual economic loss from debris flows has 

exceeded 2 billion yuan (US$ 235 million), and 

the annual loss of life from debris flows and 

landslides, many of which are actually debris 

flows, is estimated at between 500 and 1,000. 

Facilities periodically damaged by debris flows 

include 150 cities, 1,200 towns and villages, 

36 railway lines, 50,000 km (31,000 mi) of 

highways, 120,000 ha (300,000 ac) of farmland, 

and large numbers of mines, secondary roads, 

and hydroelectric facilities. In addition to the 

death and destruction from moving debris flows, 

their deposits remain to reduce flood conveyance 

in channels and the water-storage capacity in 

the region’s reservoirs. More than 360 small-tomedium-scale hydroelectric stations and more 

than 50 reservoirs were destroyed by 1991, and at 

least 1,000 reservoirs had lost significant capacity 

primarily as a result of debris flows [IMHE—

Institute of Mountain Disasters (renamed 

Hazards) and Environment, 1991].

 Jiangjia Ravine is tributary to the Xiaojiang 

River (fig. 1) which has 106 other tributaries 

that yield debris flows. The watershed of the 

Xiaojiang River is known in China as the 

“World’s Natural Museum of Debris Flows” (Cui 

and others, 1999a). That description is not an 

overstatement. Debris flows would be common 

in the Xiaojiang watershed under natural 

Table 1. Annual sediment yields of debris flows in Jiangjia Ravine. Data from Dongchuan Debris Flow 

Observation and Research Station. Total sediment discharges estimated for 1965 to 1981 range from 820,000 in 

1971 to 3,530,000 m3 in 1965 (Wang and others, 2000).

Year Sediment Discharge Number of Periods of Annual Precipitation

 ( m3 ) Debris Flow (mm)

1982 1,920,000 14 408

 1983 3,980,000 15 653

 1984 3,690,000 7 528

 1985 5,850,000 14 788

 1986 1,800,000 5 478

 1987 1,710,000 7 352

 1988 290,000 4 307

 1989 2,000,000 14 389

 1990 2,560,000 10 580

 1991 6,590,000 * 22 * 697

 1992 1,190,000 5 497

 1993 260,000 2 524

 1994 2,000,000 6 739

 1995 3,740,000 13 775

 1996 3,150,000 14 620

 1997 6,570,000 18 810

 1998 2,150,000 10 514

 1999 2,340,000 8 484

 2000 600,000 8 735

 2001 3,732,000 21 886 *

 * Peak of record (only during the period listed here for annual precipitation) 
conditions, but they are larger and more frequent 

in part because of progressive deforestation that 

began during the Tang Dynasty (A.D. 618-907) 

and intensified during the last 300-400 years 

for the smelting of copper from local mines 

(Wieczorek and others, 1987).

 The Xiaojiang is the main southern tributary 

of the Jinsha River (the fabled “River of the 

Golden Sands” in Chinese literature), which joins 

the Min River to form the upper Yangtze River, 

here known as the Chang Jiang (Long River). 

Northwest of the provincial capital of Chengdu 

(of Sichuan, north of Yunnan; fig. 1), the Min 

River descends from the Qinghai-Tibet Plateau, 

an area of high relief and frequent debris flows, to 

disgorge sediment as coarse as boulders (particles 

with diameters > 256 mm, or about 10 in). At 

this point, famed engineer Li Bing designed 

the first large-scale, hydraulically sophisticated 

system for flood control and irrigation in the 3rd

century BC. The system still functions exactly 

as he designed it, utilizing the natural flux of 

coarse sediment toward the inside of a large bend 

to separate it from flow with low concentrations 

of sediment toward the outside of the bend. 

Relatively clear water is then decanted from 

the outside of the bend through a bedrock weir 

(named “Neck of Precious Bottle”) into lowgradient canals that irrigate the Sichuan Basin, 

the so-called Granary or Rice Basket of China.

The Great Rivers of China and Erosion of the 

Landscape

 The two large rivers of China—the Yellow 

River of the north and the Yangtze of the 

south—are strikingly different. The Yellow 

River transports approximately 3 times as much 

sediment as the Yangtze on average, whereas 

the Yangtze discharges approximately 20 times 

as much water as the Yellow River (Jordaan, 

1992). Sediment yields and erosion are intense 

Figure 3. Photo of surge front on June 15, 1990. Note spray of ejected particles from surge front, especially at right 

margin (left bank). Width of surge is 20 m (66 ft). Photo by K.M. Scott.

Introduction – Why Study Debris Flows? 5 
6 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

throughout most of the Yellow River watershed, 

due in significant part to widespread deposits of 

loess, or windblown silt. Slopes covered by or 

cut into loess readily fail, and the disaggregated 

material may move as a debris flow. In contrast, 

high sediment yields and erosion rates are mainly 

confined to the rugged headwaters of the Yangtze 

watershed. There, the active mountain-building 

processes that have elevated the Qinghai-Tibet 

Plateau have formed a steep and unstable 

landscape where debris flows are common. For 

example, the annual sediment yield (volume of 

sediment only) from Jiangjia Ravine is typically 

from 1–4 million m3 (35-140 million ft3). 

Table 1 summarizes the annual sediment yields 

and the numbers of flow episodes at Jiangjia 

Ravine from 1982 to 2001. The maximum 

recorded annual yield is 6.6 million m3

(230 million ft3), which corresponds to an 

astounding denudation rate—equivalent to 

lowering the entire area drained by Jiangjia 

Ravine in a single year, by over 13.6 cm (more 

than 5 in)!

WHAT CAN WE LEARN FROM THE VIDEO?

 The video illustrates the features of debris 

flows that make them an important geologic 

process and hazard—their content of rock 

particles (sediment), high velocities, ability to 

move huge boulders, and other unique attributes 

described under the following headings. We 

recorded most of the first 24 in a sequence of 77 

rainfall-triggered surges lasting over 3 hours and 

45 minutes in Jiangjia Ravine on July 9, 1990. 

The site is renown for similar flow episodes, 

lasting between 30 minutes and over 10 hours, 

that have occurred here with summer rainstorms 

between 5 and 28 times annually and a total of 

427 times from 1965 to 2001. Segments of this 

video appear in many television documentaries 

on natural hazards, including those dealing with 

lahars. Except for their lack of coarse boulder 

snouts or fronts, explained below, the flows in 

Jiangjia Ravine are typical, in appearance and 

characteristics, of debris flows as they occur in 

steep terrain around the world.

 The characteristics and dynamics of the 

surges seen in the video were recorded by the 

staff of the Dongchuan Debris Flow Observation 

and Research Station (DDFORS), part of IMHE 

(Zhang and Xiong, 1997). Flow episodes consist 

of as many as 100 or more surges, each separated 

by less than one to tens of minutes. Each surge 

is a separate wave of moving rock fragments and 

water. Table 2 includes data for all the surges in 

the video, to and including surge 29, the second 

of 2 surges in the series that were sampled for 

sediment content. Complete data for the 77-

surge series appear by surge number in DDFORS 

records (Zhang and Xiong, 1997, p. 105-106). 

Figure 2 shows the DDFROS facilities and 

the location at which the video was made. A 

complete narration of the video, for reference by 

educators and keyed by surge number, is included 

in the appendix.

Flows of Water and Rock Particles Comprise 

a Spectrum of Increasing Sediment Content 

from Floods, to Hyperconcentrated Flows, to 

Debris Flows

 Floods consist of water containing less 

than 20 percent sediment by volume—fine 

sediment that moves in suspension and coarser 

particles that roll and saltate along the bed 

(bedload). The properties of debris flows, in 

which a slurry of sediment moves a subordinate 

amount of entrained water, are less well known 

but are the object of intense experimental study 

(cf., Iverson, 1997). Debris flows typically 

contain about 65 percent sediment by volume, 

and may be defined as containing at least 

60 percent sediment by volume (cf., Pierson 

and Costa, 1987). Least well known are the 

properties of the flows between these two end 

members—hyperconcentrated flows, which 

contain sediment in the range of 20 to 60 percent 

by volume, or 40 to 80 percent by weight. The 

occurrence and deposits of hyperconcentrated 

flow are rarely recognized, but may actually 

be common in the steeplands of volcanic and 
Table 2. Data for surges seen and sequential with those seen in the video. Data for all 77 surges in series from 

Zhang and Xiong, (1997, p. 105-106). Surges 13 and 29 were sampled (data in figure 8).

 Surge Time code Time Height Velocity Discharge Unit Surge 

 number on video* at start of (m) (m/s) (m3/s) weight volume 

 observation reach (t/m3) m3 

 (hr: min: sec)

 1 2-13/14 13:13:19 0.40 3.23 25.8 1.700 2141

 2 2-14/15 13:14:44 0.90 6.78 128.1 2.000 2626

 3 2-16/17 13:16:01 1.00 7.63 167.9 2.100 4785

 4 2-17/18 13:17:15 0.65 7.84 117.2 2.100 2051

 5 2-18-19 13:18:00 1.21 8.16 246.8 2.200 4196

 6 2-19-20 13:19:41 1.15 8.33 239.5 2.200 9221

 7 13:21:27 2.58 9.09 609.8 2.200 13100

 8 2-23/24 13:22:52 2.83** 9.30** 710.6** 2.200 23450 **

 (Only the surface of flow 8 is shown)

 9 2-24/25 13:24:30 1.66 8.16 338.6 2.200 5926

 10 2-25/26 13:25:38 2.29 8.33 496.0 2.200 10168

 11 2-27 13:26:46 2.06 8.00 412.0 2.200 7004

 12 2-28 13:27:34 1.68 8.00 336.0 2.200 7392

 13 *** 2-29/30 13:29:02 1.63 8.89 362.3 2.262** 5072

 14 2-30/31 13:29:50 1.55 8.89 344.5 2.262** 6718

 15 2-31/32 13:31:19 1.56 7.27 283.5 2.262** 4394

 16 13:32:17 2.01 7.35 369.3 2.262** 4616

 17 13:33:05 1.64 7.41 303.8 2.262** 5164

 18 13:34:09 1.39 7.04 244.6 2.262** 4280

 19 2-35/36 13:35:35 1.75 7.30 319.4 2.262** 8304

 2-37/38 (No data for small surge seen between surges 19 and 20,

 in the process of being overriden by surge 20) 

 20 2-38/39 13:37:48 1.70 8.70 369.7 2.262** 7948

 21 2-40/41 13:40:03 0.85 6.78 144.1 2.262** 2666

 22 2-41/42 13:40:48 1.31 5.88 192.6 2.262** 3274

 23 2-42/43 13:41:42 1.41 7.41 261.2 2.200 6269

 24 2-43/44 13:43:35 1.20 7.14 214.2 2.200 3748

 25 13:44:38 0.80 8.89 177.8 2.200 2845

 26 13:45:42 1.22 6.25 190.6 2.200 3526

 27 13:47:01 1.70 7.14 303.4 2.200 10468

 28 13:48:49 1.15 5.56 159.8 2.200 3276

 29 *** 13:50:20 1.40 7.69 269.2 2.180 076

 Series contained 48 more surges. Peak surge velocity in the remainder of the series was 8.33 m/s; peak height 

was 1.99 m; peak unit weight was 2.200 t/m3. Surges 75-77 were hyperconcentrated flows. 

 * The time code is one hour in advance of local time; the relative times between surges, as measured from the time 

codes and used for correlation with the data of Zhang and Xiong (1997), are accurate.

 ** Peak values of the entire series.

 *** Samples taken from these surges; sample reported from surge 14 by Zhang and Xiong (1997) is from surge 13.

What Can We Learn from the Video? 7 
8 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

semiarid terrains (cf., Pierson and Scott, 1985; 

Scott, 1988).

 Surge 1 in the video is a hyperconcentrated 

flow (data in table 2). Note that the high 

sediment content causes it to resemble dirty, 

turbulent motor oil in appearance. The body of 

surge 2 is a debris flow, but note that it is pushing 

hyperconcentrated flow that has remained in the 

channel ahead of the surge peak. Some of the 

flows in the video by Costa and Williams (1984) 

have the same appearance and behavior and are 

probably also hyperconcentrated flows.

Debris Flows Can Move Huge Boulders

 Debris flows are widely cited as capable of 

moving huge boulders. In fact, most of the 

debris flows in the western United States and 

other parts of the world have a characteristic 

snout or front of boulders, the concentration of 

which may act like a “moving dam.” Examples of 

flows with boulder-dominated fronts are recorded 

in the video by Costa and Williams (1984). This 

common feature is not present in the debris 

flows in our video, only because little sediment as 

coarse as boulders is present at Jiangjia Ravine—

the bedrock readily disaggregates to small 

fragments. The boulder seen rolling in the flow 

between surges 6 and 7 is near the maximum 

size recorded at the site, over 1 m (about 4 ft) in 

maximum dimension.

Forming Rivers of Rock

 The Jiangia Ravine watershed is underlain 

by highly fractured, metasedimentary 

and volcaniclastic siltstone and shale that 

disaggregates directly to pebble-size clasts. The 

smaller particles are predominantly elongate, 

or prismoidal, in shape. This material is 

continuously supplied to the main channels from 

hill- and valley-side slopes, by small landslides, 

dry sliding, and in the summer by wet creep at 

a visibly obvious rate (fig. 4). Bank erosion of 

previous debris flow deposits (fig. 5) adds to the 

surge volumes (flow bulking). During the storms 

that trigger the flows, slope stability throughout 

the steep source areas of Jiangjia Ravine is so 

low that access and direct observations are not 

prudent (and were not permitted in 1990). 

Nevertheless, our observations during clear 

weather suggest that the source of the flows is the 

gradual mobilization or flushing of the “reservoir” 

of deposits, during storm runoff, that have 

accumulated in the channel network since the last 

flow episode. The surges generally do not form 

by progressive upstream slope failures, as observed 

in some areas of recurrent debris flow. 

Debris Flows are Faster than Flood Waves

 At similar discharges, slurries of debris 

flow travel about twice as fast as water flows. 

Velocities of the surges typically range from 

several m/s to 10 m/s, about 10 to 33 ft/s or 7 

to over 20 mph–the range of those we see in the 

video. Velocities of most debris flows fall in this 

range. The velocity of the fastest surge in the 

video (surge 8) is 9.3 m/s (table 2), equivalent 

to 30.5 ft/s or 20.8 mph. The maximum surge 

velocity recorded at the site is 18.18 m/s (July 9, 

1998)–over 40 mph! The values are based on the 

travel times, measured by stopwatch, of the surge 

fronts in the straight, 200-m reach upstream from 

the observation point (fig. 2). In the calculations 

of flow and sediment discharge, discussed below, 

it is assumed that the debris flow surges are 

translatory waves of moving material rather than 

of form—that is, that the particles in the wave are 

moving at the speed of the wave, as opposed to 

oscillatory surges in which the wave form moves 

faster than the material within it [see the video 

of Costa and Williams (1984) for an example of 

a wave form moving through nearly stationary 

sediment]. The dominantly translatory nature 

of the surges at Jiangjia Ravine, where sediment 

moves with the flows, is clear in the video. 

We designate surge velocity in the video as c, 

celerity—the velocity of a wave form independent 

of sediment movement.

 The channel retains a significant volume of 

flow between the surges, and this material may 

cease to flow, as seen in the video, or it may flow 

continuously. Note the stationary material in 

the channel as it is overrun by all of the surges 

following surge 3.
Figure 4. Photo of tilled debris flow deposits in Jiangjia Ravine (note texture in rice-field levee at left) 

and debris cones of sediment flowing from the steep valley-side slopes. Note patterns on cone surfaces, 

indicating mass flow, in some instances at visibly detectable rates during summer dry periods. Photo by 

K.M. Scott

Figure 5. Photo of debris flow in channel, incorporating mass of material derived from bank failure 

(arrow). Note texture of deposit surface, in cutbank and on surface at lower left. Photo by K.M. Scott.

What Can We Learn from the Video? 9 
10 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

Flow Geometry—Depth and Width—and 

Channel Slope 

 The heights of individual surges typically 

range from 1–2 m (3.3–6.6 ft). The largest surge 

in the video (surge 8) is 2.83 m (9.3 ft) high. 

The highest peak recorded at the site through 

2001 was 5.5 m (18 ft). The flows range in 

width from 20.0 m (66 ft), the width of the 

channel bottom, to 27.0 m (89 ft) for surge 8. 

Slope of the reach at the site is 0.06. 

How Much Flow and Sediment are Moved by 

the Surges at Jiangjia Ravine?

The largest peak discharge of any surge in the 

video (table 2; no. 8) is 710.6 m3/s (25,000 cfs). 

The largest peak discharge measured for any surge 

at Jiangjia Ravine through 2001 is 2,913.5 m3/s, 

or 103,000 cfs (July 9, 1998). Total sediment 

yield (the volume of sediment discharged from 

the watershed) of the 77 surges, including the 

hyperconcentrated flows, is 243,000 m3 (over 

8 million ft3 ). The most sediment discharged by 

any single flow series is 2 million m3, or about 70 

million ft3 (Ou, 1999, p. 37). The sediment-yield 

volumes are derived from the total discharges 

of the surges and their measured or estimated 

sediment concentrations.

 Maximum sediment transport rates for 

each surge are not listed in Table 2, but values 

range between 29 t/s (surge 1) and 1,370 t/s 

(surge 8)—the largest transport rate for any of the 

77 surges in the series.

Why Debris Flows Destroy Manmade 

Structures–Powerful Impact Forces

 The ability of debris flows to crush many 

structures results from their high impact forces—

they are literally rivers of flowing rock fragments 

with interstitial water. The maximum unit 

weight of a surge in the video is 2.26 t/m3 (surges 

13 to 22), compared to 1.0 for pure water, only 

slightly less than the maximum recorded value at 

the site of 2.37 t/m3, corresponding to 81 percent 

sediment by volume (Wang, 1989, p. 237; Ou, 

1999, p. 37). Thus the flows are more than twice 

as dense as pure water (as well as flowing at twice 

the velocity, as noted above). The unit weight 

of the solid sediment at Jiangjia Ravine is taken 

uniformly as 2.65 t/m3 (a density of 2.65).

Like Wet Cement

 Debris flow behavior is strongly influenced 

by a highly viscous, nearly incompressible pore 

fluid composed of water with suspended fine 

sediment (Iverson, 1997). Although the property 

of viscosity does not strictly apply to granular 

mixtures, like most debris flows, viscosity has 

been measured or estimated for some flows. The 

viscosities of debris flows themselves are reported 

at over 1,000 times that of pure water at 20o

(Pierson, 1980). Viscosity of 20–30 poises is 

reported by Li and others (1983) for the flows 

at Jiangjia Ravine. That range compares with 

viscosities reported for mayonnaise, 6.3 poises, 

and wet cement, 24 poises (see table 2 of Costa, 

1984). 

Why Multiple Surges?

 Prolonged episodes of debris flow commonly 

occur as a series of separate surges, both at 

Jiangjia Ravine and elsewhere (see the video of 

Costa and Williams, 1984). Explanations include 

flow instability, which causes uniform flow to 

evolve into a series of waves (Davies, 1986; Liu 

and Mei, 1990). Based on research at Jiangjia 

Ravine in the month following the surges in our 

video, Davies and others (1991, 1992) observed 

that surges form with the continuous inflow of 

material from upstream into downstream, wider, 

and less-steep reaches that already contain a large 

volume of static debris (such as the 200-m reach 

upstream from the video site; fig. 2). Discharge 

of a surge from those reaches is triggered 

periodically at some critical point, temporarily 

depleting them, and setting the stage for another 

cycle of continuous upstream inflow that will 

again trigger episodic outflow. Between surges, 

flow commonly ceases entirely, as we see in the 

video.
Ballistic Clast Ejection—Estimating Flow 

Velocities from Runup Heights

 The fronts of the surges contain clasts as 

coarse as small boulders, but the dominant size 

class is the pebble (4-64 mm) fraction. Grainto-grain collisions are intense, and pebbles 

are constantly ejected from the moving front, 

at times as a spray of material (fig. 3). The 

spray appears to be mud, but it is mainly if not 

entirely mud-coated particles, based on the direct 

observations of the authors during this flow 

series. Ejection is intense when flow impacts 

the channel side or a barrier at a high angle, and 

cataclasis (breaking and crushing) of the pebbles 

occurs. The ballistically ejected, mud-coated 

clasts yield mud-splatter deposits that extend 

above those that are formed as the flows “run up” 

an obstacle or superelevate against the outside 

of a channel bend. Thus, based on deposits 

after the fact, applications of the energy-balance 

equation (assuming conversion of kinetic to 

potential energy) at this site could yield velocities 

that are too large. The distance (h) a flow runs 

up an obstacle is related to velocity (c) by the 

energy-balance relation, c = [2gh]1/2, where g = 

gravitational acceleration (cf., Pierson, 1985). 

However, in a large-scale flume, Iverson and 

others (1994) found that the measured velocities 

of moving debris flow exceeded those obtained 

from application of the energy-balance equation 

to the runup height (where not affected by mud 

splatter) by about 30 percent.

Estimating Cross Sections of Debris Flows

 Instantaneous debris flow discharges are 

commonly estimated by obtaining velocities 

from runup as described above, as well as by the 

superelevation of the flow surface (Δh) in a bend 

due to centrifugal force (cf., Pierson, 1985). 

Velocity (c) is related to Δh by the relation, 

c = [gΔhrc/b]1/2, where rc = centerline radius of 

curvature, and b = channel width. The velocity 

estimate is then multiplied by the cross sectional 

area to yield the rate or discharge of flow.

 Webb and others (1989) found that 

unrealistically high discharge values of debris 

flows were obtained from bends, when compared 

with corresponding values for the same flow in 

straight reaches. Compared to both upstream 

and downstream sites, the cross-sectional areas 

at bends were 1.3 to 3.6 times larger (Webb 

and others, 1989). In each location, the flow 

surface and thus the cross-sectional area was 

reconstructed by connecting the peak flow levels 

as indicated by deposits on both sides of the 

channel with a straight line. This large difference 

in discharges could not be explained, but one 

suggestion was the presence of static material in 

curves. The video indicates the probable cause 

of the discrepancy in discharge values–the flow 

surface in bends is markedly concave (fig. 6). 

This conclusion corresponds with observations of 

bend-surface concavity during flume experiments 

(Iverson and others, 1994). Figure 7 shows the 

interpretations (assuming straight flow surfaces) 

of the cross sectional area in a case where the 

discharge obtained from a bend is twice that of a 

discharge from a straight reach.

Knickpoints

 Knickpoints are vertical, transverse “falls” in 

channel elevation that are scoured by erosion and 

which commonly migrate upstream. Knickpoints 

as much as 1–1.2 m in height form during 

the surge series at Jiangjia Ravine. They were 

observed but not photographed during the late 

stages of the flows of July 9, 1990. As described 

by Davies and others (1991 and 1992), they 

are probably associated with channel incision. 

However, during the series in the video and a 

previous series on June 15, 1990 (fig. 3), they 

were transient features developed in deposits 

only temporarily in the channel, and they did 

not result in any notable change in mean bed 

elevation.

Why and How Do We Seek to Identify the 

Deposits of Old Debris flows?

 Debris flow occurrence is rarely as frequent 

and predictable as at Jiangjia Ravine. Elsewhere, 

potential flow hazards may be evident only 

from the deposits of previous flows. How can 

What Can We Learn from the Video? 11
12 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

we recognize these deposits, and thus their past 

as well as the possible or even probable future 

occurrence of debris flows? 

 1. They have a fine-grained, commonly muddy 

matrix. Debris flows are commonly called 

mudflows because of their content of fine 

sediment [mud = the total of silt-size sediment 

(0.004–0.0625 mm) and clay-size sediment 

(< 0.004 mm; < 0.005 mm in Chinese data)]. 

The flows and deposits at Jiangjia Ravine 

typically contain 2 to 5, and as much as 10 

percent clay-size sediment by weight (Kang, 

1989). Figure 8 shows histograms of sample 

A, a complete analysis of all size fractions in 

a flow in Jiangjia Ravine; B and C are the 

partial analyses of surges 13 and 29. The 

samples of moving flows were taken with a 

suspended sampler with a restricted orifice, 

thereby excluding the coarsest fractions. 

In addition, the fine fractions of the two 

samples were not analyzed. Otherwise, the 

distributions in B and C would be similar to 

that of A.

 The amount of silt- and clay-size material is 

useful for determining debris flow origin, and 

samples D and E of figure 8 are deposits that 

are cohesive (or muddy), and noncohesive 

(or granular), respectively. These two 

textural subpopulations help us distinguish 

lahars of landslide and meltwater origins, 

respectively, at volcanoes (Scott and others, 

2001). However, facies of lahars with mainly 

cohesive deposits may have very little fine 

sediment, as in the boulder-rich bars of the 

channel faces of the 1980 lahar in the North 

Fork Toutle River (Scott, 1988, fig.15). 

R.M. Iverson (written commun., 2002) has 

noted formation of a fines-free levee facies at 

Figure 6. Photo of longitudinal roll waves and concave surface of right-to-left flow in bend on June 15, 1990. For 

scale, this bend is visible in the video—for example during surge 10. Observer in left foreground does not indicate 

scale. Photo by Kang Zhicheng
Figure 7. Diagrammatic cross-sections of flow illustrating the differences in cross-sectional area (and thus, 

discharge) as they depend on reconstruction of the flow surface from deposits. Case B1–B1’: assumption of 

straight line connecting highest deposits on each side of channel; case B2–B2’: observed concave surface at Jiangjia 

Ravine, yielding cross-sectional area in accord with those from upstream and downstream cross-sections A–A’ and 

C–C’.

A

B

C

A'

B'

A A' C C'

B1 B1'

B2 B2'

C'

PLAN VIEW OF CHANNEL BED

CROSS SECTIONS OF CHANNEL

Cross-sectional

area = 10 m2

Cross-sectional

area = 20 m2

Cross-sectional

area = 10 m2

Cross-sectional

area = 10 m2

What Can We Learn from the Video? 13
14 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

 the large-scale flume noted above. Typical 

alpine debris flows that move with boulderrich fronts, as noted above in contrast to the 

flows at Jiangjia Ravine, also leave lateral 

levees dominated by boulder-size clasts. 

 2. They are commonly bimodal (two peaks in 

histograms of sediment size). For example, 

sample D in figure 8 has a primary mode 

or peak in a cobble-size fraction of the size 

distribution–between 128 and 256 mm, and 

a secondary mode in a sand fraction–between 

0.125 and 0.25 mm. The coarse mode 

represents particles in the “dispersed phase;” 

the finer mode is sediment in the muddy 

matrix or “continuous phase.” The coarse 

mode is like the plums dispersed throughout a 

plum pudding. With the other features listed 

here, we can identify debris flow deposits 

from this bimodal, “plum-pudding” texture. 

 3. They contain a large range of sediment sizes; 

that is, they are poorly sorted (high values of 

σG; fig. 9). In figure 9, several of the samples 

in figure 8 are plotted as cumulative curves 

on a graph with a probability ordinate, on 

which normal distributions (a bell-shaped 

distribution in a histogram) plot as straight 

lines. Note that, excluding the primary mode, 

sample D is close to a normal distribution, as 

seen both in the histogram in figure 8 and the 

nearly straight line in figure 9.

 The fewer the fractions in a sediment 

sample, the more steeply the line representing 

their cumulative distribution is sloped and the 

better the sorting (low values of σG; fig. 9). 

Note the better sorting of flood deposits 

represented by samples G and H. Sample 

G is a deposit of coarse gravel resulting from 

bedload transport in flood flow, and sample 

H is the deposit of a sand layer deposited 

by a flood. For comparison, with both the 

poorer sorting produced by debris flows and 

the better sorting of flood deposits, sample 

F is the deposit of a hyperconcentrated flow. 

Figure 10 shows the deposit of a debris flow 

overlying that of a flood or hyperconcentrated 

flow.

 4. They are commonly massive (without 

stratification). The multiple surges at 

Jiangjia Ravine, where they spread over a 

downstream flood plain (fig. 11), yield single 

massive, matrix-supported units, analogous 

to the successive surges of material from a 

large debris flow flume (Major, 1997). The 

series of texturally and compositionally 

homogeneous surges yield massive composite 

units without obvious stratigraphic 

breaks, indicating a need for caution when 

interpreting flow magnitudes and frequencies 

from stratigraphy, particularly in alluvial fan 

environments.

 Because the stratigraphic units are commonly 

of composite construction, and therefore 

relatively uniform, graded bedding is poorly 

developed. Wang and others (1999) note the 

occurrence of normal grading (upward fining) in 

some units.

Can People Be Warned That a Debris Flow is 

Coming?

 Warning times of 20-45 minutes at the 

observation site are based on threshold values of 

rainfall intensity and antecedent precipitation 

(Ou, 1999). For predictive purposes, rainfall data 

are telemetered from recording stations high in 

the watershed. The flows in the video occurred 

with little precipitation at the observation site.

 Various devices for event warnings (flow 

is occurring) have been tested at this location 

(e.g., Kang, 1990). They include Acoustic 

Flow Monitors (AFM’s)—solar-powered, 

microprocessor-based field computers linked 

to exploration-model geophones that detect 

the specific frequency of moving debris flows 

(LaHusen, 1998). Arrays of AFM’s are widely 

used for detection of lahars. In addition, lives 

can be saved by educating the residents of 

vulnerable areas–like the many towns in the 

valleys of mountainous southern China–to 

recognize ground vibrations as the possible signal 

of an approaching debris flow, and to go to high 

ground immediately. With this knowledge—

Education for Self Warning and Evacuation 
Figure 8. Texture (particle size distribution) of debris flow deposits, shown as histograms. A, Debris flow at 

Jiangjia Ravine (Li and others, 1983); B, Surge 13; C. Surge 29; D, Cohesive (muddy) debris flow deposit in North 

Fork Toutle River—peak flow facies of 1980 lahar from Mount St. Helens (fig. 17, Scott, 1988); E, Noncohesive 

(granular) debris flow deposit in South Fork Toutle River—1980 lahar 35.6 km downstream from Mount St. 

Helens (fig. 20, Scott, 1988); F, Lahar-runout flow, 1982 in Toutle River (fig. 41, Scott, 1988); G, Fluvial gravel 

representing bedload in Toutle River (“pre-lahar alluvium,” fig. 22, Scott, 1988); H, Fluvial sand in 1980-81 flood 

berm of Toutle River (fig. 41, Scott, 1988).

Complete Sample

Surge 13

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

Flood gravel

Lahar-runout deposit

Noncohesive deposit—

South Fork lahar

Cohesive deposit—

North Fork lahar

-10 -5 10 Φ

1024 512

0

1

5

0.031 0.001 mm

-10 -5 10 Φ

1024 512

0

1

5

0.031 0.001 mm

PERCEN

T PERCEN

T

0

10

20

30

40

PERCEN

T

0

10

20

30

40

PERCEN

T

0

10

20

30

40

50

PERCENT

0

10

20

30

40

PERCENT

0

10

20

30

40

PERCENT

PERCEN

T

HYPERCONCENTRATED FLOW

Mount St. Helens – Toutle River

FLOOD DEPOSITS

Mount St. Helens – Toutle River

Jiangjia Ravine

Mount St. Helens – Toutle River

A.

F.

G.

H. Flood sand

B.

C. Surge 29

D.

E.

finer than 0.15 mm

finer than 0.15 mm

finer than

0.625 mm

Φ = –log2 mm

What Can We Learn from the Video? 15
16 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

(ESWEV)—people can, in effect, be their own 

AFM’s (Scott and others, 2001).

Mitigation and Countermeasures

 The video records the flows as they pour 

from a mountain front across an alluvial 

fan. The rugged topography indicates the 

difficulties in stabilizing slopes and reducing 

the sediment flux into channels. In order to 

maintain its function as a natural laboratory, 

no formal engineering works are present in 

the upstream portion of the main channel of 

Jiangjia Ravine. However, in addition to a 

national program of soil conservation, measures 

that specifically target other watersheds that 

yield debris flows include planting trees and 

constructing plant hedges to stabilize hillslopes 

and retard flows. Engineering measures are 

primarily check or sabo dams, and flumes that 

Figure 9. Selected data in figure 8 plotted as cumulative curves of the size distributions. 

Values of sorting (σ) as the graphic standard deviation of Folk (1980), 

σG = (Φ84 - Φ16)/2. Φ values defined as in Figure 8. 

Figure 10. Photo of cutbank showing lighter-colored 

debris flow deposit overlying deposits of flood or 

hyperconcentrated flows. Photo by J.J. Major.

0.1

0.2

0.5

1

2

5

10

20

30

40

50

60

70

80

90

95

98

99

99.8

99.9 -6

64

-5

32

-4

16

-3

8

-2

4

-1

2

0

1

1

0.5

2

0.25

3

0.125

4

0.0625

5

0.031

6

0.016

7

0.008

8

0.004

9

0.002

phi

 mm

SEDIMENT SIZE

CUMULATIVE PERCENT

EXPLANATION

Debris flow

Hyperconcentrated flow

Flood flow

F

σG = 1.15

H

σG = 0.75

D

σG = 3.70

A

σG = 4.85

E

σG = 4.40
function as “drop structures,” diverting flow to 

lower gradients in order to reduce erosion. In 

one cited example (Ou, 1999) of 29 watersheds, 

a total of 12 towns, 100 villages, 15,300 hectares 

of farmland, 16,000 people, and property valued 

at 1.1 billion yuan (US $130 million) have been 

protected by these measures at a total cost of 45 

million yuan (US $5 million).

Figure 11. Photo of downstream reach of Jiangjia Ravine where debris flow surges spread and deposit lateral 

levees. Photo by J.J. Major.

ACKNOWLEDGMENTS

 This report and the new narration benefit 

greatly from the advice of Robert C. Watters, 

University of Nevada; Oldrich Hungr, University 

of British Columbia; and Thomas C. Pierson and 

Carolyn L. Driedger, U.S. Geological Survey, 

each of whom has used the unedited video, in 

spite of the original narration, to introduce both 

beginning and advanced students to debris flows. 

Acknowledgments 17
18 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

REFERENCES CITED, AND FOR FUTHER 

STUDY(*)

(For Chinese authors, surnames are followed by given 

names)

Chen, J., 1989, A study on debris flow warning in 

China: Proceedings of Japan-China Symposium on 

Landslides and Debris Flows, Tokyo, p. 177-181. 

*Costa, J.E., 1984, Physical geomorphology of debris flows, 

in Costa, J.E. and Fleisher, P.J., eds., Development and 

Applications of Geomorphology: Berlin, Springer-Verlag, 

p. 268-317.

*Costa, J.E., and Williams, G.R., 1984, Debris flow dynamics: U.S. 

Geological Survey Open-File Report 84-606 (a video).

Cui, P., 1992, Study on conditions and mechanics of debris flow 

initiaion by means of experiment: Chinese Science Bulletin, v. 

37, no . 9, p. 759-763.

*Cui, P., 1999, Impact of debris flow on river channels in the 

upper reaches of the Yangtze River: International Journal of 

Sediment Research, v. 14, p. 201-203.

Cui, P., Thornes, J., and Guan, J., 1996, International 

Symposium Interpravent 1996–Garnisch-Partenkirchen, 

Tagungspublikation, Bd. 3, p. 1-3-112.

*Cui, P., Wei, F., and Li, Y., 1999a, Sediment transported by debris 

flows to the lower Jinsha River: International Journal of 

Sediment Research, v. 14, p. 67-71.

Cui, P., Liu, S., Tang, W., and Chen, Y., 1999b, Debris flow 

monitoring and forecasting in China, progress and prospect: 

1999 Annual Report Dongchuan Debris Flow Observation and 

Research Station, p. 17-23.

Cui, P., Liu, S., and Tan, W., 2000, Progress of debris flow forecast 

in China (in Chinese): Journal of Natural Disasters, v. 9, no. 2, 

unpaginated.

*Davies, T.R.H., 1986, Large debris flows–a macroviscous 

phenomenon: Acta Mechanica, v. 63, p. 161-178.

Davies, T.R.H., Phillips, C.J., Pearce, A.J., and Zhang, X.B., 1991, 

New aspects of debris flow behavior: Proceedings, Japan-U.S. 

Symposium on Snow Avalanches, Landslides and Debris Flow 

Prediction and Control.

Davies, T.R.H., Phillips, C.J., Pearce, A.J., and Zhang, X.B., 1992, 

Debris flow behavior–an integrated overview: Proceedings of 

Symposium on Erosion, Debris Flows, and Environment in 

Mountain Regions, IASH Pub. 209, p. 217-225.

Dongchuan Institute of Debris Flow Control, 1987, Debris flow of 

Xiaojiang River basin in photographs: Sichuan Publishing 

House of Science and Technology, 37 p.

Du R., 1989, Debris flows and their countermeasures in China: 

Proceedings of Japan-China Symposium on Landslides and 

Debris Flows, Tokyo, p. 191-194.

Du, R., Li, H., Tang, B., and Zhang, Z., 1995, Debris flow studies in 

China in the last 30 years: Journal of Chinese Geography, v. 5, 

no. 4, p. 90-102.

Folk, R.L., 1980, Petrology of sedimentary rocks: Austin, Texas, 

Hemphill Publishing Company,182 p.

Institute of Mountain Disasters and Environment, 1991, A manual 

of the distribution of debris flow disaster and its dangerous 

regionalization map in China: 1:6,000,000 scale map and 

accompanying report, 8 p. [presently, Institute of Mountain 

Hazards and Environment]

*Iverson, R.M., 1997, Physics of debris flows: Reviews of 

Geophysics, v. 35, p. 245-296. 

Iverson, R.M., LaHusen, R.G., Major, J.J., and Zimmerman, C.L., 

1994, Debris flow against obstacles and bends: Dynamics and 

deposits (abs.): EOS, v. 75, no. 44, p. 274.

*Iverson, R.M.., Reid, M.E., and LaHusen, R.G., 1997, Debris-flow 

mobilization from landslides: Annual Review of Earth and 

Planetary sciences, v. 25, p. 85-138.

Jan, C.D., Wang, Y.Y., and Han, W.L., 2000, Resistance reduction 

of debris-flow due to air entrainment [at Jiangjia Ravine]: 

in Wieczorek, G.F., Naeser, N.D., eds., Debris-Flow Hazards 

Mitigation: Mechanics, Prediction, and Assessment, 

Proceedings of the Second International Conference on 

Debris-Flow Hazards Mitigation, Taipei, Taiwan, p. 369-372.

Jordaan, J.M., 1992, Railway debris flow and flood disaster 

protection works in Mainland China: Die Siviele Engenieur in 

Suid Afrika, November, Technical Note, p. 367-377.

Kang, Z., 1989, A mechanical analysis on the occurrence of debris 

flow: Proceedings of Japan-China Symposium on Landslides 

and Debris Flows, Tokyo, p. 206-208.

Kang, Z., 1990, Motion characteristics of debris flow at Jinagjia 

Gulley, Yunnan Province, China: Beijing, International 

Research and Training Center on Erosion and Sedimentation, 

38 p.

*LaHusen, R.G., 1998, Detecting debris flows using ground 

vibrations: U.S. Geological Survey Fact-Sheet FS-236-96, 2 p.

Li, J., Yuan, J., Bi, C., and Luo, D., 1983, The main features of the 

mudflow in Jiang-Jia Ravine: Zeitschrift fur Geomorphologie, 

N.F., Bd. 27, p. 325-341.

Liu, K.F., and Mei, C.C., 1990, Waves in a fluid mud layer flowing 

down an incline: Proceedings, International Symposium on 

the Hydraulics/Hydrology of Arid Lands, Hydraulics Division 

of the American Society of Civil Engineers, San Diego, p. 403-

409.

*Major, J.J., 1997, Depositional processes in large-scale debris-flow 

experiments: Journal of Geology, v. 105, p. 345-366.

Ou, G., 1999, Sediment hazards and counter measures in China: 

1999 Annual Report, DDFROS, p. 35-39.
Pierson, T.C., 1980, Erosion and deposition by debris flows at 

Mt. Thomas, North Canterbury, New Zealand: Earth Surface 

Processes, v. 5, p. 227-247.

Pierson, T.C., 1985, Iniation and behavior of the 1980 Pine Creek 

and Muddy River lahars, Mount St. Helens, Washington: 

Geological Society of America Bulletin, v. 96, p. 1056-1069.

*Pierson, T.C., and Scott, K.M., 1985, Downstream dilution of 

a lahar: transition from debris flow to hyperconcentrated 

streamflow: Water Resources Research, v. 21, p. 1511-1524.

*Scott, K.M., 1988, Origins, behavior, and sedimentology of lahars 

and lahar-runout flows in the Toutle-Cowlitz River System: 

U.S. Geological Survey Professional Paper 1447-A, 74 p.

*Scott, K.M., Macías, J.L., Naranjo, J.A., Rodriguez, S., and 

McGeehin, J.P., 2001, Catastrophic debris flows transformed 

from landslides in volcanic terrains–Mobility, hazard 

assessment, and mitigation strategies: U.S. Geological Survey 

Professional Paper 1630, 59 p.

*Takahashi, T., 1991, Debris flows: Balkema, Rotterdam, 165 p.

Wang, Y., 1989a, The main static characteristics of debris flow 

in the southwestern mountain areas of China: Proceedings 

of Japan-China Symposium on Landslides and Debris Flows, 

Tokyo, p. 237-239.

Wang, Y., 1989b, An approach to rheological models for debris 

flow research: Proceedings, Fourth International Symposium 

on River Sedimentation in Beijing, p. 714-721.

Wang, Z.Y, Wai, O.W.H., and Cui, P., 1999, Field investigation into 

debris flow mechanism: International Journal of Sediment 

Research, v. 14, p.10-22.

Wang, Y., Jan, C, and Yan, B., 2000, Debris flow structure and 

rheology: National Natural Science Foundation of China, 216 

p. In Chinese.

*Webb, R.H., Pringle, P.T., and Rink, G.R., 1989, Debris flows 

from tributaries of the Colorado River, Grand Canyon National 

Park, Arizona: U.S. Geological Survey Professional Paper 1492, 

39 p.

Wieczorek, G.F., Wu, J., and Li, T., 1987, Deforestation and 

landslides in Yunnan, China: International Erosion Control 

Association, Proceedings of Conference 18, Reno, Nevada; 

February, 1987, p. 183-196.

Zhang, J., and Xiong, G., 1997, Data collection of kinematic 

observation of debris flows in Jiangjia Ravine, Dongchuan, 

Yunnan (1987-1994): Beijing, Science Press, 258 p. In 

Chinese.

References 19

APPENDIX

APPENDIX

Narration. A. During introductory black-and-white film segment showing flows and sampling at Jiangjia 

Ravine.

B. During remainder of video/DVD.

A. Debris flows are slurries of rock and water that flow like wet concrete. They are an important way that 

sediment is transported in mountainous areas. Debris flows are also a significant geologic hazard. 

 Each summer, in arid and mountainous SW China, debris flows are triggered by rainstorms. Each 

episode may consist of more than 100 separate waves, or surges, lasting over several hours. In the 1960’s, 

sampling procedures were primitive (narrated as technician runs from surge front).

B.

SURGE NUMBER 

 AND VEL0CITY (c)

 IN M/S NARRATION WITH SURGES, BY NUMBER

1 This is the first of 77 surges.

 Each series may begin with surges of water or, as here, a type of flow

c = 3.23 called hyperconcentrated flow.

 Hyperconcentrated flow is a mixture of water and sediment. 

 It has more sediment than a flood but less than a debris flow.

 Debris flows look like wet concrete; hyperconcentrated flows look like motor oil.

2 The second surge, beginning as debris flow, pushes and mixes with the 

hyperconcentrated flow already in the channel. 

c = 6.78

3 As surge 3 leaves the mountain front, note the emerald green areas. These are 

fields of rice and sweet potatoes cultivated on the deposits

c = 7.63 of larger debris flows during the 1980’s.

 The debris flow fronts are the deepest part of each surge.

 The fronts contain the coarsest clasts in the flow.

 At this site, surges occur at regular intervals, from one to several minutes. A 

single series of surges may continue for over 10 hours.

4 Grain-to-grain contact in the turbulent front is intense.

 Masses of mud that seem to be splashing from the front are actually

c = 7.84 ballistically ejected, mud-coated pebbles.

 A spray of ejected pebbles precedes the surge.

 By this time, flow ceases between the surges.

 The channel remains full of slurry waiting to be remobilized.

Appendix 23
24 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

B. (Continued)

SURGE NUMBER 

 AND VEL0CITY (c)

 IN M/S NARRATION WITH SURGES, BY NUMBER

5 Note how fast the surges travel–about twice as fast as the same size of water wave. 

We are seeing the flows at actual speed.

c = 8.16 Debris flows are more than twice as dense as water without sediment.

 These two factors–very dense flows moving very fast–create the high impact 

forces that enable debris flows to destroy many manmade structures.

6 As the series builds initially, each surge is larger and faster.

 Flow now splashes to the top of the main terrace.

c = 8.33

Between 6 and 7 Debris flows can move huge boulders.

 Here the size is limited by the bedrock of the watershed, which is mainly weak, 

easily broken shale.

 This boulder is over 1 m or nearly 4 ft in length.

 Note the people on the bank for scale.

7 [not photographed]

8 This is the surface of the largest and fastest surge in the entire series.

 Velocity of the front is over 9 m/s, or 20 mi/h.

c = 9.30 Debris flow sediment, seen here between surges, consists of two phases–coarse 

particles, mainly pebbles in these flows, that are dispersed and suspended in a 

matrix of sand, silt and clay. 

9 We are looking directly at the front of the flow.

 As it hits the bank, we can sense the impact force. 

c = 8.16 A barrage of pebbles is ejected.

 The ground vibrations of approaching large debris flows can be detected by 

instruments known as Acoustic Flow Monitors, and a warning signal can be 

radioed downstream in time for evacuations.

10 Longitudinal waves form as the flow rolls up or superelevates against the bank on 

the inside of a bend.

c = 8.33
B. (Continued)

SURGE NUMBER 

 AND VEL0CITY (c)

 IN M/S NARRATION WITH SURGES, BY NUMBER

11 In the film from the 1960’s at the beginning of this video, this channel had not 

been cut, and flows spread across the entirely valley. That

c = 8.00 film was made at this location.

12 Mud, the term for particles of silt and clay size, causes debris flows to be widely 

known as mudflows. 

c = 8.00 Scientists prefer the term debris flow because mud is generally less than 25% of 

most debris flows, and some have only a few percent mud.

 The streaks in the flow, parallel to the banks, are lines of shear as flow approaches 

the channel boundary.

13 Surge 13 has as high a unit weight as any in the series–2.26 t/m3 vs. 1.0 for pure 

water. 

c = 8.89 That value is only slightly less than the maximum value recorded for any debris 

flow at this site–2.38 t/m3.

14 In contrast to the dangerous techniques of the 1960’s, samples are now taken by 

lowering the torpedo-like cylinder into the flow with a steel cable.

c = 8.89 

15 Note how the flow is disturbed by irregularities in the bank.

 Measurements of runup or superelevation height after the fact, in order

c = 7.27 to estimate velocity, can be highly variable.

19 As we watch the final surges recorded on video, we will review some 

characteristics of debris flows. 

c = 7.30 As surge 19 begins, note that the upstream terrain is steep, barren, and climate is 

semiarid. Worldwide, debris flows are especially common in areas with these 

characteristics.

 Between 19 and 20 Debris flows are slurries of water and sediment.

 They consist of coarse fragments dispersed or seemingly floating in a fine-grained 

matrix.

Appendix 25
26 Debris Flows—Geologic Process and Hazard—Surge Sequence at Jiangjia Ravine, Yunnan, China

B. (Continued)

SURGE NUMBER 

 AND VEL0CITY (c)

 IN M/S NARRATION WITH SURGES, BY NUMBER

20 Debris flows contain more than 60 percent sediment by volume.

 Flow with less sediment, seen in the first two surges, is described

c = 8.70 as hyperconcentrated flow.

 It contains less than 60 but more than 20 percent sediment.

21 The fronts of each surge are turbulent, like surge 21.

 The front contains the coarsest material.

c = 6.78 Cobbles and boulders collide violently in the front, extruding smaller particles.

22 Debris flows have high impact forces that can destroy many structures and crush 

most buildings.

c = 5.88 This is because they are more than twice as dense as water, and nearly twice as 

fast as a surge of water the same size.

23 Debris flows are an important process of sediment transport.

 In a single year, episodes of flows like these have removed enough

c = 7.41 material from this watershed to lower its entire 19-square-mile surface by 5 

inches.

24 Debris flow are also an important geologic hazard.

 Debris flow, along with landslides, many of which are viscous debris

c = 7.14 flows, take an average of 500-1,000 lives each year in China and cause 

hundreds of millions of dollars in damage.
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY

Order U.S. Geological Survey (USGS) publications by 

calling the toll-free telephone number 1-888-ASK-USGS 

or contacting the offices listed below. Detailed ordering 

instructions, along with prices of the last offerings, are given 

in the current-year issues of the catalogue “New Publications 

of the U.S. Geological Survey.”

Books, Maps, and Other Publicat ions

By Mail

Books, maps, and other publications are available by mail 

from—

U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Publications include Professional Papers, Bulletins, WaterSupply Papers, Techniques of Water-Resources Investigations, 

Circulars, Fact Sheets, publications of general interest, single 

copies of permanent USGS catalogs, and topographic and 

thematic maps.

Over the Counter

Books, maps, and other publications of the U.S. Geological 

Survey are available over the counter at the following USGS 

Earth Science Information Centers (ESIC’s), all of which are 

authorized agents of the Superintendent of Documents.

• Anchorage, Alaska—Rm. 101, 4230 University Dr.

• Denver, Colorado—Bldg. 810, Federal Center

• Menlo Park, California—Bldg. 3, Rm 3128, 

345 Middlefield Rd.

• Reston, Virginia—1C402, USGS National Center, 

12201 Sunrise Valley Dr.

• Salt Lake City, Utah—2222 West, 2300 South

• Spokane, Washington—Rm. 135, U.S. Post Office 

Bldg., West 904 Riverside Ave.

• Washington, D.C.—Rm. 2650, Main Interior Bldg., 

18th and C Sts., NW

Maps only may be purchased over the counter at the 

following USGS office:

• Rolla, Missouri—1400 Independence Rd.

Electronically

Some USGS publications, including the catalogue “New 

Publications of the U.S. Geological Survey” are also available 

electronically on the USGS’s World Wide Web home page at 

http://www.usgs.gov

Preliminary Determination of Epicenters

Subscriptions to the periodical “Preliminary Determination 

of Epicenters” can be obtained only from the Superintendent 

of Documents. Check or money order must be payable to 

the Superintendent of Documents. 

Order by mail from—

Superintendent of Documents

Government Printing Office

Washington, DC 20402

Information Periodicals

Many Information Periodicals products are available through 

the systems or formats listed below:

Printed Products

Printed copies of the Minerals Yearbook and the Mineral 

Commodity Summaries can be ordered from the Superintendent 

of Documents, Government Printing Office (address above). 

Printed copies of Metal Industry Indicators and Mineral 

Industry Surveys can be ordered from the Center for Disease 

Control and Prevention, National Institute for Occupational 

Safety and Health, Pittsburgh Research Center, P.O. Box 18070, 

Pittsburgh, PA 15236-0070.

Mines FaxBack: Return fax service

 1. Use the touch-tone handset attached to your fax machine’s 

telephone jack. (ISDN [digital] telephones cannot be used 

with fax machines.)

 2. Dial (703) 648-4999.

 3. Listen to the menu options and punch in the number of 

your selection, using the tough-tone telephone.

 4. After completing your selection, press the start button on 

your fax machine.

CD-ROM

A disc contining chapters of the Minerals Yearbook (1993-

95), the Mineral Commodity Summaries (1995-97), a 

statistical compendium (1970-90), and other publications is 

updated three times a year and sold by the Superintendent of 

Documents, Government Printing Office (address above).

World Wide Web

Minerals information is available electronically at http://

minerals.er.usgs.gov/minerals/

Subscription to the catalog “New Publications of the U.S. 

Geological Survey”

Those wishing to be placed on a free subscription list for the 

catalog “New Publications of the U.S. Geological Survey” 

should write to—

U.S. Geological Íurvey

903 National Center

Reston, VA 20192
Books and Other Publications

Professional Papers report scientific data and interpretations 

of lasting scientific interest that cover all facets of USGS 

investigations and research.

Bulletins contain significant data and interpretations that are 

of lasting scientific interest but are generally more limited in 

scope or geographic coverage than Professional Papers.

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations 

of wide interest to professional geologists, hydrologists, and 

engineers. The series covers investigations in all phases of 

hydrology, including hydrogeology, availability of water, quality 

of water, and use of water.

Circulars are reports of programmatic or scientific information 

of an ephemeral nature; many present important scientific 

information of wide popular interest. Circulars are distributed 

at no cost to the public.

Fact Sheets communicate a wide variety of timely information 

on USGS programs, projects, and research. They commonly 

address issues of public interest. Fact Sheets generally are two or 

four pages long and are distributed at no cost to the public.

Reports in the Digital Data Series (DDS) distribute large 

amounts of data through digital media, including compact 

disc-read-only memory (CD-ROM). They are high-quality 

interpretive publications designed as self-contained packages 

for viewing and interpreting data and typically contain data 

sets, software to view the data, and explanatory text.

Water-Resources Investigations Reports are papers of an 

interpretive nature made available to the public outside the 

formal USGS publications series. Copies are reproduced 

on request (unlike formal USGS publications) and are also 

available for public inspection at depositories indicated in 

USGS catalogs.

Open-File Reports can consist of basic data, preliminary 

reports, and a wide range of scientific documents on USGS 

investigations. Open-File Reports are designed for fast release 

and are available for public consultation at depositories

Maps

Geologic Quadrangle Maps (GQ’s) are multicolor geologic 

maps on topographic bases in 7.5- or 15-minute quadrangle 

formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, 

surficial, or engineering geology. Maps generally include brief 

texts; some maps include structure and columnar sections 

only.

Geophysical Investigations Maps (GP’s) are on topographic 

or planimetric bases at various scales; they show results of 

surveys using geophysical techniques, such as gravity, magnetic, 

seismic, or radioactivity, which reflect subsurface structures that 

are of economic or geologic significance. Many maps include 

correlations with the geology.

SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Miscellaneous Investigations Series Maps or Geologic 

Investigations series (I’s) are planimetric or topographic bases 

at various scales; they present a wide variety of format and 

subject matter. The series also includes 7.5-minute quadrangle 

photogeologic maps on planimetric bases and planetary 

maps.

Information Periodicals

Metal Industry Indicators (MII’s) is a free monthly newsletter 

that analyzes and forecasts the economic health of five metal 

industries with composite leading and coincident indexes: 

primary metals, steel, copper, primary and secondary aluminum, 

and aluminum mill products.

Mineral Industry Surveys (MIS’s) are free periodic statistical 

and economic reports designed to provide timely statistical 

data on production, distribution, stocks, and consumption 

of significant mineral commodities. The surveys are issued 

monthly, quarterly, annually, or at other regular intervals, 

depending on the need for current data. The MIS’s are 

published by commodity as well as by State. A series of 

international MIS’s is also available.

Published on an annual basis, Mineral Commodity Summaries

is the earliest Government publication to furnish estimates 

covering nonfuel mineral industry data. Data sheets contain 

information on the domestic industry structure, Government 

programs, tariffs, and 5-year salient statistics for more than 90 

individual minerals and materials.

The Minerals Yearbook discusses the performance of the 

worldwide minerals and materials industry during a calendar 

year, and it provides background information to assist in 

interpreting that performance. The Mineral Yearbook consists 

of three volumes. Volume I, Metals and Minerals, contains 

chapters about virtually all metallic and industrial mineral 

commodities important to the U.S. economy. Volume II, Area 

Reports: Domestic, contains a chapter on the mineral industry 

of each of the 50 States and Puerto Rico and the Administered 

Islands. Volume III, Area Reports: International, is published 

as four separate reports. These reports collectively contain the 

latest available mineral data on more than 190 foreign countries 

and discuss the importance of minerals to the economies of 

these nations and the United States.

Permanent Catalog

“Publications of the Geological Survey, 1879–1961” and 

“Publications of the Geological Survey, 1962–1970” are 

available in paperback book form and as a set of microfiche.

“Publications of the Geological Survey, 1971–1981” is 

available in paperback book form (two volumes, publications 

listing and index) and as a set of microfiche.

Annual supplements for 1982, 1983, 1984, 1985, 1986, and 

subsequent years are available in paperback book form.

Scott, K.M., and Wang, Y. — U.S. Geological Survey Professional Paper 1671

DEBRIS FLOWS–GEOLOGIC PROCESS AND HAZARD–ILLUSTRATED BY A SURGE SEQUENCE AT JIANGJIA RAVINE, YUNNAN, CHINA