Dendrogeomorphic Evidence and Dating of

Recent Debris Flows on

Mount Shasta, Northern California

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1396-B

Dendrogeomorphic Evidence and Dating of

Recent Debris Flows on

Mount Shasta, Northern California

By CLIFF R. HUPP, W. R. OSTERKAMP, and 

JOHN L. THORNTON

DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS ON 

MOUNT SHASTA, NORTHERN CALIFORNIA

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1396-B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1987
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging-in-Publication Data

Hupp, C.R.

Dendrogeomorphic evidence and dating of recent debris flows on Mount Shasta, northern California.

(U.S. Geological Survey professional paper; 1396-B)

Bibliography: p. 33

Supt.ofDocs.no.: 119.16:1396-6

1. Mass-wasting California Shasta, Mount, Region. 2. Dendrochronology California Shasta, Mount, Region. I.

Osterkamp, W.R. II. Thornton, John L III. Title. IV. Series: Geological Survey professional paper; 1396-B.

United States. U.S. Geological Survey. 

QE598.2.H87 1987 551.3 86-600195

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225
CONTENTS

	Page

Conversion factors --------------------------------------- iv

Abstract ------------------------------------------------ Bl

Introduction -------------------------------------------- i

Dendrochronological analysis ------------------------ 2

Types of botanical evidence of debris flows ------------ 3

Previous study -------------------------------------- 5

Site description ------------------------------------- 5

Hydrogeomorphology ---------------------------- 5

Vegetation -------------------------------------- 7

Methods ------------------------------------------------ 9

Sampling design ------------------------------------ 9

Field and laboratory routine ------------------------- n

Analyses of magnitude and frequency of debris flows - - 11

Age and spatial distribution of debris flows --------------- 12

Whitney Creek -------------------------------------- 12

The 1985 debris flow ---------------------------- 12

Earlier debris flows ----------------------------- 12

Age and spatial distribution of debris flows Continued 

Bolam Creek ------------------------------------

Mud Creek -------------------------------------

Ash Creek --------------------------------------

Cold Creek, (sites 26 through 28) -------------

Gravel Creek -----------------------------------

Site 29 -------------------------------------

Sites 30, 31, 32 ------------------------------

Inconstance Creek -------------------------------

Nonglacial streams ------------------------------

Panther Creek ------------------------------

Cascade Gulch ------------------------------

Diller Canyon -------------------------------

Discussion ------------------------------------------

References -------------------------------------------

Appendix: Detailed site descriptions -----------------

B15

16

17

22

22

25

27

27

29

29

31

31

31

33

35

ILLUSTRATIONS

FIGURE 1. Sketch showing types of botanical evidence of debris flows ---------------------------------------------------------- B4

2. Photographs of examples of botanical specimens in dendrogeomorphic study ------------------------------------------ 6

3. Map of study area showing streams and study sites ----------------------------------------------------------------- 10

4. Chart showing age and downvalley distribution of debris flows on Whitney Creek ------------------------------------ 14

5. Cross sections of Whitney Creek channel and depositional areas ----------------------------------------------------- 16

6. Bar graph of debris-flow frequency per century by magnitude class on Whitney Creek -------------------------------- 17

7. Chart showing age and downvalley distribution of debris flows on Bolam Creek -------------------------------------- , 18

8. Bar graph of debris-flow frequency per century by magnitude class on Bolam Creek ---------------------------------- 19

9. Cross section of Mud Creek 3 kilometers above dam --------------------------------------------------------------- 20

10. Chart showing age and downvalley distribution of debris flows on Mud Creek ---------------------------------------- 21

11. Bar graph of debris-flow frequency per century by magnitude class on Mud Creek ------------------------------------ 22

12. Chart showing age and downvalley distribution of debris flows on Ash Creek ---------------------------------------- 23

13. Bar graph of debris-flow frequency per century by magnitude class on Ash Creek ------------------------------------- 24

14. Plan-view map of upper Ash Creek -------------------------------------------------------------------------------- 24

15. Two cross sections on upper Ash Creek ---------------------------------------------------------------------------- 25

16. Cross section showing terraces on Ash Creek near Military Pass Road- ----------------------------------------------- 26

17, 18. Photographs of:

17. Ash Creek channel banks above Military Pass Road--------------------------------------------------------- 27

18. Saplings on debris-flow lobe near site 29 on Gravel Creek --------------------------------------------------- 28

19, 20. Cross sections of:

19. Gravel Creek near site 29 -------------------------------------------------------------------------------- 29

20. Western white pine affected by debris flow on Inconstance Creek -------------------------------------------- 29

21. Photograph of Inconstance Creek near site 33 ---------------------------------------------------------------------- 30

22. Bar graph of age and frequency of debris flows on Mount Shasta back to 1580 ---------------------------------------- 32

23. Bar graph of debris-flow activity by basin -------------------------------------------------------------------------- 32

TABLES

TABLE 1. Summary of debris flows on Mount Shasta --------------------------------------

2. Summary of debris flows and magnitudes on Gravel Creek in the vicinity of site 29

Page

B13 

28

ill
IV CONTENTS

CONVERSION FACTORS

For the convenience of readers who prefer to use inch-pound units rather than the metric 

International System units used in this report, the following conversion factors are provided:

Multiply metric unit

millimeter (mm)

meter (m)

kilometer (km)

square kilometer (km2)

cubic meter (m3)

megagram (Mg)

megagram per square kilometer

per year ((Mg/km2)/yr)

by

0.03937

3.281

0.621

0.386

35.31

1.1

2.87

to obtain inch-pound unit

inch (in)

foot (ft)

mile (mi)

square mile (mi2)

cubic foot (ft3)

ton, short (2,000 Ib)

ton, (short) per square mile

per year ((ton/mi2)/yr)
DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS ON MOUNT SHASTA,

NORTHERN CALIFORNIA

DENDROGEOMORPHIC EVIDENCE AND DATING OF RECENT 

DEBRIS FLOWS ON MOUNT SHASTA, NORTHERN CALIFORNIA

By CLIFF R. HUPP, W.R. OSTERKAMP, and JOHN L. THORNTON

ABSTRACT

Evidence of debris flows is common along the glacially fed streams 

of the Mount Shasta volcano, California. These streams are Whitney 

Creek, Bolam Creek, Mud Creek, Ash Creek, Gravel Creek, and 

Inconstance Creek. Debris flows since 1580 can be documented by 

studying trees damaged by or growing on debris flows. Dates obtained from tree-ring analysis proved consistent with documented 

records of debris flows. Debris-flow dates in conjunction with geomorphic evidence permit the development of magnitude and frequency 

relations over a period of about 400 years.

Dendrogeomorphic evidence shows that debris flows are a common 

occurrence on many Mount Shasta streams. Debris flows traveling at 

least 2 kilometers have occurred at a frequency of about 10.5 debris 

flows per century; certain basins are more active than others, the 

Gravel Creek and Mud Creek basins are among the most active, and 

Inconstance Creek basin is the least active. Small debris flows are 

more frequent and usually do not move as far downslope as large 

debris flows. Cyclic scouring and filling by debris flows, in and adjacent to stream channels and on debris fans, is suggested by dendrogeomorphic evidence and seems to be related to event magnitude and 

frequency. Distinct periods of heightened debris-flow activity and 

quiescent periods occur in individual basins and are apparently related to glacial and valley wall stability and meltwater supply. Debris flows of all magnitudes appear to be the major surficial geomorphic agent during noneruptive times that sculpture the channels and 

develop large alluvial fans.

INTRODUCTION

Dendrochronological analyses are means of obtaining dates of occurrence of many important geomorphic 

events. Magnitude and frequency information are useful in the prediction of floods, landslides, debris flows, 

and most other hydrogeomorphic hazards. Where historic records are short or lacking, tree-ring study is the 

most accurate method for obtaining magnitude and frequency data over the past several hundred-year period. 

Botanical evidence in combination with geomorphic 

evidence allows for the interpretation and determination of the relative importance of various geomorphic 

processes.

Debris flows a process at the fluid end of the massmovement spectrum are poorly sorted slurries of 

rock, soil, and water. These flows, also termed "lahars" 

when they occur on volcanoes, may originate from a 

variety of mechanisms (Mullineaux and Crandell 1962; 

Pierson 1980a, b; Costa and Jarrett 1981; Janda and 

others 1981; Costa 1984). Debris flow velocities range 

from less than 1 m/s to more than 40 m/s (Janda and 

others 1981), and they can flow down stream channels 

for many tens of kilometers (Crandell 1971; Janda and 

others 1981). Deposits may be preserved as overbank 

deposits, as terraces within channels, or as lobate 

sheets on debris fans (Curry 1966; Pierson 1980b; Costa 

and Jarrett 1981). Impact on trees from debris flows 

depends on flow velocity, thickness, and size of transported clasts. Effects of the impact on trees can range 

from tranquil burial of lower trunks to complete destruction of large areas of forests (Janda and others 

1981; Hupp and Sigafoos 1982; Hupp 1984; Costa 

1984). Despite the coarse, sometimes bouldery texture 

of debris-flow sediments (Pierson 1980a, b; Costa and 

Jarrett 1981), woody vegetation may readily establish 

on these deposits.

Debris flows are common along many streams draining the Mount Shasta volcano, particularly those 

streams which head at alpine glaciers. These flows may 

represent the major surficial geomorphic agent during 

noneruptive periods on the mountain. During eruptive 

periods, debris flows may affect large portions of the 

Mount Shasta area. Deeply sculpted valleys, overlapping depositional terraces, and broad alluvial fans 

have developed downslope, respectively, in many 

Mount Shasta basins largely through debris-flow activity. Cyclic scouring and filling by debris flows, in and 

adjacent to the stream channels and fans, are suggested by dendrogeomorphic evidence and appears to 

be related to magnitude, frequency, and channel gradient.
B2 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

The purpose of this report is to present the result of 

the studies to develop a debris-flow history (magnitude 

and frequency) for several streams on Mount Shasta 

over the past several centuries. The dating of Mount 

Shasta debris-flow activity from the 1500's is based on 

combined geomorphic and botanical evidence. Secondary purposes were to show that botanical evidence allows geomorphic characterizations of debris-flow deposition and scour, through time and for inference on the 

relative effects of debris flows of various magnitudes 

and frequencies.

DENDROCHRONOLOGICAL ANALYSIS

Woody vegetation grows along most streams except 

in very arid regions. In relatively humid areas, trees 

are usually the dominant vegetal cover over most of the 

landscape. Woody species are perennials, living 

through the harsh portion of a year, usually winter, by 

becoming dormant. When conditions conducive to 

growth recur, woody plants break dormancy and begin 

growing again. Seasonal growth results in the production of an annual increment of wood, called a tree ring.

Trees grow in height only at the tips of branches. 

Growth in girth is from a vascular cambium (woodproducing tissue) that sheaths the entire plant just 

under the bark. Thus, an annual growth increment is a 

cone of new wood overtopping that of previous years. 

Cones viewed in cross section are a series of concentric 

rings. Trees produce annual increments throughout 

their lives, which can be over 1000 years but more 

commonly a few years to several hundred years.

Scientists use tree-ring dating (dendrochronology) 

for determining the age of geomorphic surfaces or 

events simply by counting the number of rings since 

germination or damage. A count of tree rings from an 

increment core taken from the base of a stem yields the 

age of the stem so long as each year is represented by 

a single ring. The dendrochronological technique of 

cross dating (Stokes and Smiley, 1968; Cleaveland, 

1980) is used to ensure that dating errors are not introduced by the possible occurrence of missing and multiple rings. Sigafoos (1964) and Phipps (1967) describe 

tree growth in relation to hydrogeomorphic studies.

Dendrochronologic methods have been widely used 

in dating the occurrence of hillslope and fluvial geomorphic events and in determining rates of processes 

(LaMarche, 1968; Alestalo, 1971; Sigafoos and 

Hendricks, 1972; Shroder, 1978; Hupp, 1983). Woody 

vegetation physically damaged by geomorphic events 

or growing on deposits provides a means for dating past 

events. The basic principles of tree-ring dating have 

been outlined extensively by Sigafoos (1964), 

LaMarche (1968), Alestalo (1971), Helley and

LaMarche (1973), and Yanosky (1983). Floods, mudflows, debris flows, and debris avalanches can have 

numerous affects on woody vegetation, including 

partly felling tree trunks, scarring stems, and creating 

bare areas where plants can become established 

(Sigafoos, 1964; Shroder, 1978; Butler, 1979; Hupp, 

1983).

Published studies centering on the use of dendrogeomorphic evidence for estimation of debris-flow frequency and magnitude have not been extensive. However, some notable studies have either suggested the 

use of botanical evidence in debris-flow study or used 

botanical evidence to study other forms of mass wasting. In California, Jackson (1977) gives an over 500- 

year account of mudflows near Big Sur. Additionally, 

he developed a mudflow stratigraphy along streams 

using tree-root zones to age mudflow strata. This 

method also estimates relative magnitude. Other similar studies in the California Mountains include 

Stewart and LaMarche (1967), LaMarche (1968), 

Helley and LaMarche (1973), and Hupp (1984). In the 

Pacific Northwest, Mullineaux and Crandell (1962) 

have suggested the use of botanical evidence in dating 

recent debris flows on Mount St. Helens. The age and 

effects of mass wasting on woody vegetation has been 

studied by Swanson and others (1981) and Miles and 

others (1984). Currently, several scientists are using 

dendrochronology in their studies of debris flows on 

volcanoes in the Cascade Range (R.J. Janda, U.S. Geological Survey, oral commun., 1984). In the Colorado 

Rocky Mountains, the use of botanical evidence has 

been suggested by Sharpe (1974), Costa and Jarrett 

(1981) and Costa (1984). Several debris flows on Mount 

Elbert, Colo., have recently been tree-ring dated by 

C.R. Hupp, and J.E. Costa (U.S. Geological Survey, 

written commun., 1984). Langenheim (1956) used vegetation to interpret a large debris flow in the Elk Range 

of Colo. Shroder (1978) conducted a dendrochronological analysis of mass wasting in Utah. In the Mackenzie 

Mountains of Canada, Parker and Jozsa (1973), Butler 

(1979), and Gardner (1982) have used dendrochronology to date landslides. Sauchyn and others (1983) have 

evaluated botanical methods other than dendrochronology, for determining debris-flow dates in the 

central and the southern Canadian Rocky Mountains. 

In the Eastern United States, debris avalanches have 

been dated through tree-ring analyses by Flaccus 

(1959), White (1979), Kochel and other (1982), and 

Hupp (1983). The importance of mass wasting and 

botanical evidence in the Eastern United States, has 

been stressed by Hack and Goodlett (1960) and Hack 

(1965). In Scandinavia, Rapp (1963), and Rapp and Nyberg (1981) have studied debris flows and suggested the 

use of dendrochronological analysis. Alestalo (1971)
DENDROGEOMORHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B3

and Schweingruber (1983) review European studies of 

dendrochronology in relation to mass wasting.

TYPES OF BOTANICAL EVIDENCE OF DEBRIS FLOWS

Debris flows can damage or destroy trees in or adjacent to their paths. Trees that survive a debris flow 

provide the most accurate dates for a particular event. 

When the trees are not killed, the effects of a debris 

flow can be manifested in several ways, usually as 

some deformation of the stem with subsequent changes 

in wood anatomy or serial tree-ring pattern. These deformations have been categorized into four basic types 

(Hupp, 1983: 1984): (1) eccentric annual growth, 

(2) suppression and release sequences, (3) tilting and 

adventitious sprouting along the parent stem, and 

(4) corrasion of the stem by transported debris. The 

analysis of cross-dated cores and cross sections of stems 

having one or more of these deformations usually 

yields several confirmations of a date for a particular 

event.

Eccentric annual growth and suppression-release sequences both involve serial ring-width measurements. 

Eccentric annual growth (fig. 1A) is produced by 

growth of the stem in an inclined position. One side of 

the stem, depending on species, will produce a thicker 

ring relative to the opposite side after the stem has 

been tilted. For example, conifers will produce thicker 

rings on the downslope side of the tilt (compression 

wood) and thinner rings on the upslope side of the tilt 

(tension wood). The overall appearance of a cross section exhibiting eccentric growth is a period of relatively 

concentric rings prior to tilting, followed by an abrupt 

shift to eccentric ring growth after tilting (fig. 1). The 

date of the event which tilted the tree is within 1 year 

of the onset of eccentric growth. In areas subjected to 

prolonged and deep snow cover, trees growing on slopes 

may be tilted due to snow push. This type of eccentricring production is, however, a gradual shift to eccentricity rather than an abrupt shift associated with 

episodic events such as a debris flow. Many tilted trees 

have debris piled on the upstream side deposited during a debris flow; furthermore they grow in flat valley 

bottoms which makes snow push rather unlikely.

Suppression and release sequences (fig. 1C) appear 

as a period of relatively narrow rings followed by an 

abrupt shift to wide rings. This type of sequence can be 

caused by any number of events that would remove 

nearby trees that compete for required resources 

(water, light). When these competitors are removed, 

the tree is "released" and a period of greater growth 

(wide rings) often follows. Trees growing adjacent to 

the path of a debris flow that removed neighboring 

trees may be released after the debris flow. Conversely,

should a slow-moving debris flow deposit a substantial 

layer of sediment around the tree, a period of suppression may ensue. Regardless, release or suppression related to debris-flow activity generally occurs abruptly. 

Gradual shifts in ring width, which resemble suppression and release, are more typically associated with 

climatic variability (Fritts, 1976). This line of evidence 

for a particular date must be used with a measure of 

caution and substantial replication of the date must be 

found in other specimens. Furthermore, trees near the 

site and unaffected by debris-flow activity should be 

analyzed to rule out particular ring patterns which 

may be climatically induced. Suppression and release 

sequences are the least accurate dating technique. One 

to a few years may be required for a tree to begin released or suppressed growth owing to inherent lag 

times associated with ring width patterns (Fritts, 

1976).

Severe tilting or partial burial can cause adventitious sprouting along the parent stem. These sprouts 

begin growing within one year after tilting and provide 

an excellent line of evidence (Hupp, 1983) when replicates are found for a particular date of an event. Tilt 

sprouting is easily recognized in the field owing to the 

distinctive growth form produced. However, adventitious sprouting is uncommon in gymnosperm plants 

(conifers), which form the bulk of the tree species on 

Mount Shasta.

The corrasion of tree stems by debris flows (fig. ID) 

damages the cambium. This corrasion can result in 

termination of radial growth where the tree was 

struck. In subsequent years the scar will be increasingly covered by callus growth until the damaged area 

is completely covered and the cambium is once again 

continuous around the trunk. Cross sections through 

the scarred portion of the trunk can yield the exact year 

of damage. Often the season of occurrence can be determined by the location of early wood or latewood at the 

outside edge of the scarred wood. Increment cores taken 

at different angles on either side of a scar and small 

wedges of wood through the side of the scar make dating possible without destroying the tree.

In areas where a debris flow removed vegetation and 

created sites for vegetation establishment, an approximate age for the debris flow may be obtained by coring 

the base of trees growing on the new surface (fig. 1) to 

their biological center (pith). Tree age may be used to 

date surfaces, although not necessarily as accurately or 

with as much confidence as other dating techiques. The 

time between the cessation of the debris flow and ecesis 

(plant establishment) is variable (Sigafoos and 

Hendricks, 1969), therefore only a minimum age may 

be estimated. However, because of the nature of regeneration of vegetation on debris-flow deposits, it is rea-
B4 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

B

Debris-flow 

surface

B

FIGURE 1. Types of botanical evidence of debris flows. A, eccentric growth; B, age of surface; C, suppression and

release; D, corrasion scar.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B5

sonable to assume that the deposit is not significantly 

older than the trees when many trees (cohorts) on a 

deposit are about the same age (even-aged stand). Preliminary studies on Mount Shasta indicate that from 1 

to 5 years elapse after the cessation of the debris flow 

before tree species begin ecesis (Hupp unpublished observations, 1982 through 1985; Sigafoos and 

Hendricks, 1969).

Between 1982 and 1985, about 1,100 trees were analyzed for evidence of debris-flow activity on Mount 

Shasta. Specimens from these trees included cores, 

cross sections, and wedges. Examples of these specimens after sanding and interpretation are shown in 

figure 2.

PREVIOUS STUDY

The earliest study to use tree-ring dates on Mount 

Shasta debris flows was conducted by Beardsley and 

Cannon (1930). They studied a site along Mud Creek 

for 4 years following the 1924 debris flow. They also 

found geobotanical evidence for a debris flow in the late 

1500's and another in about 1900. Beardsley and 

Cannon (1930) also found that, although many trees 

were not immediately killed by the debris flow, death of 

trees continued for 4 years probably as a result of 

burial and subsequent suffocation and desiccation of 

roots. Some trees were buried to a depth of about 5 m.

Dickson and Crocker (1953) used tree ages on the 

Mud Creek debris-flow area to confirm soil chronosequence dates. They found botanical evidence for four 

debris flows including the 1924 event. The three other 

dates were about 1388, 1747, and 1892; these are minimum ages and do not allow for period of vegetation 

establishment. Glauser (1967) determined that trees 

growing on the 1892 surface, determined by Dickson 

and Crocker (1953; 1954), to have an average age of 68 

years in 1964. This would suggest that two years were 

necessary for vegetation establishment. Sollins and 

others (1983), also working on the Mud Creek debrisflow area, used tree rings to determine fire dates and 

apparently confirm the dates of debris flows suggested 

by previous studies.

Miller (1980) studied debris-flow activity on several 

streams around Mount Shasta. Specific dates of recent 

flows are not given. However, Miller reports that at 

least three debris flows occurred since about 1770 on 

Inconstance Creek; more than five debris flows on 

Gravel Creek in the last several hundred years; at least 

five debris flows on Ash and Cold Creeks in the last 200 

years; more than seven debris flows in the vicinity of 

Mud and Squaw Valley Creeks since about 1880; and 

many debris flows on Whitney and Bolam Creeks in the 

last several hundred years. Although details of the dendrochronological analysis are not given, Miller (1980) 

suggests that botanical evidence of debris flows is common along many of the mountain's streams.

Other researchers on Mount Shasta have employed 

tree-ring methods incidentally to confirm an age of a 

recent deposit for soil chronosequences (Jenny 1980). 

No systematic dendrochronological effort has been conducted around the mountain except along Mud Creek. 

Even on Mud Creek, except for fire scars (Sollins and 

others, 1983), the bulk of the dates came from tree-age 

dating which is the least accurate type of botanical 

evidence. All of the previous studies give little or no 

details of their dendrochronologic methodology.

SITE DESCRIPTION

HYDROGEOMORPHOLOGY

Mount Shasta is a massive stratovolcano located at 

the southern end of the Cascade Range in northern 

California. Four volcanic centers have produced lava 

flows, pyroclastic flows, and domes, since Pleistocene 

time (Christiansen 1982). Both hot and cold debris 

flows have occurred relatively frequently on most 

major streams draining the mountain (Miller, 1980; 

Hupp, 1984). Basins which head at alpine glaciers have 

had the largest and most frequent debris-flow activity 

(Hupp, 1984); these include Whitney, Bolam, Mud, 

Ash, Cold, Gravel, and Inconstance Creeks (fig. 3).

Mount Shasta is surrounded by broad fans which 

begin relatively short distances away from the peaks. 

Deep stream valleys, which continue for long distances 

away from most Cascade Volcanoes (Crandell and 

others, 1979), are restricted on Mount Shasta presumably because of pronounced fan development. A result of fan development is the rapid spreading of debris 

flows on fans at relatively short distances away from 

the mountain. On other volcanoes in the Cascade 

Range, with deep radiating stream valleys, debris 

flows tend to travel considerably farther (Crandell and 

others, 1979). No streams directly draining Mount 

Shasta are gaged. Thus, detailed gaging station records 

are unavailable. Peak flows generally occur in the 

warm months as a result of snowmelt or glacial runoff. 

The glacial meltwater streams have little or no discharge during winter months. The greatest amounts of 

discharge and fluctuation in discharge occur in midsummer. Aside from glacial floods (jokulhlaup), the 

midsummer diurnal fluctuation in streamflow accounts for a large part of discharge variations; the maximum daily discharge is about four times that of the 

minimum discharge (Meier, 1964). The slope of the 

daily streamflow hydrograph is consistent from day to 

day, season to season, and glacier to glacier (Meier,
B6 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

Gravel Creek, 1728 Terrace

FIGURE 2. Examples of botanical specimens in dendrogeomorphic study. A, increment core of tree indicating minimum age of terrace on 

Gravel Creek; B, cross section of red fir (cohort) on debris lobe along Gravel Creek; C, wedge through scar in tree near Whitney Creek; 

D, eccentric growth after the 1962 Ash Creek debris flow; E, scarring and eccentric growth from tree near Whitney Creek; F, scar cross 

section from tree affected by the historic 1924 debris flow on Mud Creek.

Gravel Creek, 

250 year old 

red fir

One of a cohort on 

1728 debris-flow

FIGURE 2. Continued.

1964). There is no direct relation between precipitation 

and runoff except during late summer (Meier and 

Tangborn, 1961). However, the correlation between 

temperature and runoff can be significant if temperature measurements are made a number of days prior to 

the discharge measurement (Meier, 1964).

Glacier-streamflow records indicate periodic high 

discharges of water are usually associated with temporarily dammed meltwater under the glacier or near an 

unstable glacier tongue (Meier, 1964). Some outburst 

floods are minor and recognizable only on streamflow

records, others are large enough to destroy roads and 

bridges, the largest can be truly catastrophic (Meier, 

1964)." Outburst floods can occur at periodic intervals 

with no direct relation to meteorologic conditions, 

while others appear to be directly related to unusually 

warm temperatures or volcanic activity (Meier, 1964; 

Janda and others, 1981).

Sudden outbursts of water can rapidly accumulate 

(bulk) large amounts of sediment from bed, banks, and 

valley wall failures and ultimately form a debris flow. 

This hydrogeomorphic scenario may be the principal 

cause of debris flows on Mount Shasta. The most recent 

debris flow on Mount Shasta occurred on July 6, 1985, 

along Whitney Creek; fresh calving at the lowermost 

glacial tongue of Whitney Glacier was observed and is 

thought to have created an outburst flood and the subsequent debris flow (W.R. Osterkamp, oral commun., 

1985).

Some generally related observations can be made 

that are apparent along all studied streams: (1) Small 

debris flows occur frequently and usually do not travel 

as far downstream as medium to large flows; (2) large 

debris flows occur less frequently than small flows and 

usually travel farther downstream; (3) debris flows 

tend to degrade (bulk) high on the slope and aggrade 

(debulk) low on the slope, and large debris flows may 

degrade in areas where subsequent small flows aggrade, producing overlapping strata in the channel incisement; (4) subsequent debris flows may remove 

dendrogeomorphic evidence of previous flows; 

(5) debris-flow terrace deposits are usually lobate in 

plan morphometry and discrete in distribution, a feature more pronounced in upstream reaches; (6) channel 

gradient appears to exert substantial control on 

the depositional characteristics of debris flows; and 

(7) high-cut banks have stratigraphic evidence of many 

large prehistoric flows
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B7

Whitney Creek 

scarred during 

1935 debris-flow

FIGURE 2. Continued.

The first two observations are characteristics shared 

with water floods; and, except that both floods and debris flows tend to flow in stream channels, the similarities between the two are limited. The viscous nature of 

debris flows (Pierson, 1985) permits the development of 

geomorphic features precluded in fluvial activity for 

example, perched stream channels, super elevated 

levee deposits, relatively high-relief lobate debris 

splays indicative of flow stagnation, and overlapping 

surge deposits formed during the same event. The valley sections of upper reaches are deeply incised into 

pyroclastic slopes which probably served as a source for 

debris through landsliding. Valley bottoms of these 

upper reaches are usually dominated by frequent small 

debris-flow lobes and terraces or are highly degraded 

from a recent large event. The valley sections in lower 

reaches have much less local relief and are dominated 

by large, infrequent debris-flow deposits, commonly 

forming part of a broad fan. Evidence of small debris 

flows in the lower reaches appears relatively minor, 

often wholly in-channel benches.

A consequence of periodic large debris flows is the 

development of large debris fans (Pierson, 1980a) 

which characterize the lower Mount Shasta slopes in 

the vicinity of major streams. The debris fans begin 

about midway on the mountain depending on gradient 

and length of time of debris-flow activity. Likewise 

length of deep incisement appears to be related to the 

length of debris flow history.

Ash Creek,

eccentric

growth

FIGURE 2. Continued.

The reader is directed to other chapters in this series 

(Blodgett and others, in press; Osterkamp and others, 

1986) for detailed accounts of the physical environment of Mount Shasta streams and adjacent areas.

VEGETATION

The forests of the Mount Shasta area fall into two 

major types: Coniferous Forest and Desert Woodland
B8 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

Whitney Creek 

scarred and 

tilted in 1974

FIGURE 2. Continued.

(Munz, 1959). The Desert Woodland is restricted to the 

lower west-facing slopes in the area of the WhitneyBolam alluvial fan. Munz (1959) describes the Northern Juniper subdivision of the Desert Woodland as an 

open forest of trees 3 to 18 m tall on brush covered 

slopes. The principal species are western juniper (Juniperus occidentalis), Jeffrey pine (Pinus jeffreyi), and 

basin sagebrush (Artemisia tridentata).

Most of the mountain (75 80 percent of area) is of the 

Coniferous Forest Type, within this type five subdivisions grow on Mount Shasta: Douglas Fir Forest, Yellow Pine Forest, Red Fir Forest, Lodgepole Forest, and 

Subalpine Forest (Munz, 1959). The boundaries of 

these subdivisions are generally determined by elevation and grade from one forest to another. The lowermost forest, Douglas Fir Forest, occurs up to 1375 m in 

elevation on the northern, eastern, and southern 

slopes. Common species include Douglas fir (Pseudotsuga menziesii), Tanbark-oak (Lithocarpus densi- 

/Zora), and sugar pine (Pinus lambertiana). Trees in

this forest grow up to 60 m high and may form dense, 

nearly pure stands of Douglas fir. The Yellow Pine 

Forest is a common, diverse forest growing at a land 

elevation of from 1,100 to 1,675 m. Trees range in size 

from 23 to 60 m tall in extensive continuous forests; 

common species include Ponderosa pine (Pinus ponderosa), sugar pine, incense cedar (Libocedrus decurrens), white fir (Abies concolor), Douglas fir, and California black oak (Quercus kellogii). The Red Fir Forest 

grows at a land elevation of from 1,675 and 2,300 m. 

Trees form dense stands and range from 30 to 50 m tall; 

common species include: California red fir (Abies magnified), sugar pine, western white pine (Pinus monticola), white fir, Jeffrey pine, and lodgepole pine (Pinus 

conforta).The Douglas Fir, Yellow Pine, and Red Fir 

Forests form the bulk of the forest within the study 

area on the northern, eastern, and southern threequarters of the mountain. The Lodgepole Forest occurs 

at elevations above 2,000 m and at slightly lower elevations on the northern quarter of the mountain in the
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B9

FIGURE 2. Continued.

vicinity of Gravel and Inconstance Creeks. Trees grow 

in open stands 15 to 21 m tall, composed largely of 

lodgepole pine. The Subalpine Forest occurs at tree line 

and grows downslope for a few hundred meters at land 

elevations from 2600 to 2900 m. No study sites were 

located at these elevations, although some of the 

species of this forest were occasionally found at the 

uppermost study sites. Principal species of this forest 

include: Whitebark pine (Pinus albicaulis), limber pine 

(Pinus flexilis\ lodgepole pine, and alpine willow 

(Salix petrophila). Nomenclature follows that of Little 

(1979).

Fires and lumbering have created extensive patches 

of open areas in most of these forests. Dense thickets of 

manzanita (Artostaphylos patula and other spp.), 

mountain misery (Chamaebatia foliolosa), California 

lilac (Ceanothus spp.), mountain-mahogany (Cerocarpus betuloides), madrone (Arbutus menziesii), and 

saplings of forest-tree species occur in disturbed areas. 

Cooke (1940) provides a description of the flora of 

Mount Shasta within the framework of a now dated 

lifeform classification.

The tree species that occur on or near debris flows at 

Mount Shasta include: California red fir, California 

black oak, Canyon live oak, Douglas fir, incense cedar, 

lodgepole pine, Ponderosa pine, sugar pine, western 

juniper, western white pine, and white fir. All of the 

above species were used in the dendrochronological 

analysis. Willows (Salix spp.) are common along 

streambanks but were rarely used in the dendrochronological analysis. Several species of shrubs grow 

on older debris-flow surfaces (cf. Dickson and Crocker, 

1953 and 1954; and Sollins and others, 1983).

The northwest-facing quarter of Mount Shasta is noticeably drier than other parts of the mountain owing 

to a rain-shadow effect. Vegetation on this side of the 

mountain reflects the more xeric conditions by being 

relatively sparse, with a greater dominance of Ponderosa pine and xeric shrubs. Western juniper (largely 

absent on other parts of the mountain) occurs on the 

lower fan slopes here.

Relatively recent debris-flow deposits typically support noticeably younger forests; very recent deposits 

may be largely devoid of woody vegetation or with 

sparse seedlings or saplings. Forests growing on deposits less than 400 years old are generally the same 

age except for scattered older trees not killed by debrisflow passage of those affected by subsequent events. 

However, in many places, fire and lumbering (over the 

last century) have complicated the picture.

METHODS 

SAMPLING DESIGN

Ten streams draining Mount Shasta were investigated for dendrogeomorphic evidence of debris flows. 

These streams are (counterclockwise from WhitneyBolam Creek, fig. 3) Whitney and Bolam Creeks, Diller 

Canyon, Cascade Gulch, Panther Creek, Mud Creek, 

Cold Creek, Ash Creek, Gravel Creek, and Inconstance 

Creek. Sites for intensive study on most of the streams 

were selected to facilitate determinations of downvalley extent of any particular debris flow. Only one 

site each was investigated on Inconstance Creek, Panther Creek, and Cascade Gulch (fig. 2). These streams 

were judged to pose little threat to human activity after 

initial reconnaissance because of relative debris-flow 

inactivity or rapid dispersion of debris flows high on 

the mountain.

Most intensive study sites are located along reaches 

relatively easily accessed by roads. However, during 

the course of 4 years of study, on streams with more 

than one study site, nearly all reaches between the 

uppermost and lowermost study sites have been investigated. No sites were above tree line or more than 

22 km from Mount Shasta peak. Seven sites were in-
BIO DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

41°35' 12215'

EXPLANATION

^>.

31J Site number

10 MILES

10 KILOMETERS

FIGURE 3. Study area in northern California. Study sites are numbered 1 through 37, beginning with Whitney Creek.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. Bll

vestigated on Whitney Creek, four sites on Bolam 

Creek, two sites on Diller Canyon, seven sites on Mud 

Creek, three sites on Cold Creek, seven sites on Ash 

Creek, four sites on Gravel Creek, and one site each on 

Inconstance Creek, Cascade Gulch, and Panther Creek 

(fig. 3). Generally, each site consists of a reach 1 to 

2 km long and as wide as the alluvial valley bottom 

which is rarely more than 0.5 km wide.

FIELD AND LABORATORY ROUTINE

Field routine at each site consisted of (1) determination and extent of debris-flow deposition, scour, or both, 

through ground traverses, topographic maps, and 

aerial photography; (2) removal of increment cores, 

cross sections, and wedges from trees growing on or 

near the debris-flow surfaces using increment borers 

and handsaws; and (3) field analysis of wood samples 

for age and ring pattern. Trees sampled for age of surface were cored as near to the base of the tree as possible. Young trees of certain species can be aged by 

counting branch whorls, thus avoiding coring or cross 

sectioning. Trees sampled to obtain age of a scar or 

other deformation were cross sectioned or had a wedge 

removed at the point of scarring or deformation. Old or 

deeply imbedded scars can be aged by coring on either 

side of the scar, although the possibility of missing 

some of the rings formed since scarring is distinctly 

increased. The quality of information gained from 

scarred trees usually warrants a cross section or wedge.

Trees selected for dendrochronological analysis were 

either growing on debris-flow deposits with their root 

collars indicating germination after surface deposition 

or bearing obvious deformations indicative of debrisflow damage or both. Detailed field notes were taken 

that described the character and location of the debrisflow deposit, the location and type of botanical evidence 

for each tree sampled, and age of deposit (when known). 

Data, by site from each stream, were tabulated, noting 

amount and type of evidence for each possible debrisflow date. The location, extent, and age of each investigated debris flow were recorded and mapped where possible. A debris-flow stratigraphy is revealed in exposed 

streambanks on many of the studied streams. Thicknesses of some recent, dated debris flows were estimated from the amount of depositions above root zones 

exposed along cut banks.

Most cores and cross sections were returned to the 

laboratory in Reston, Va., for microscopic examination 

and cross dating. Cores are typically placed in holders 

and sanded with increasingly fine grit. Cross sections 

and cores are sanded to facilitate ring boundary determinations under microscopic observation. A few cores 

are then standardized (Fritts, 1976) and plotted. These

were measured for serial ring width. Ring width values 

data were then used to pinpoint suppression and release sequences not associated with debris-flow activity 

to rule out climatic variation. Probable dates of debris 

flows from field and laboratory analysis were tabulated. Depending on the type and amount of botanical 

evidence for a particular date, it is either included in 

the debris-flow history or considered questionable and 

not retained for later magnitude and frequency analysis. Generally, a date was kept if at least five specimens 

substantiated the date, or an obvious corrasion scar 

could be found that coincided with other types of botanical evidence.

ANALYSES OF MAGNITUDE AND FREQUENCY 

OF DEBRIS FLOWS

Frequency of past debris flows is relatively easy to 

determine from tree-ring data over the past 200 years 

or so. However, owing to removal of geomorphic and 

botanical evidence by subsequent debris flows, increasingly older events become more difficult to date. Small 

debris-flow deposits are particularly susceptable to removal by medium to large debris flows. Thus, the possibility of missing an old small event exists. Fortunately, 

fan deposits, owing to shifting channel positions, can be 

preserved for old medium-sized events. Large events 

are usually quite easy to detect with minimal field experience. Only the lifespan of the regional tree flora, 

fire, and lumbering limit dating of large events. Nevertheless, the minimum age for any surface with living 

woody plants can be determined.

Resolution of magnitude of a debris flow, like frequency, becomes more difficult with increasing age of 

the event. The bulk of botanical evidence for a particular event generally cannot be used as an estimation of 

magnitude. The elevation, distance downslope, and 

thickness of debris-flow deposits are, however, reasonable estimators of relative magnitude. The degree to 

which a flow was contained in the fan channel is also a 

reasonable estimate of magnitude.

The debris flows were separated into three magnitude categories small, medium, and large. This separation is based primarily on distance along a stream for 

which there is evidence of passage or deposition of a 

debris flow and the degree to which it was confined to 

the channel incisement. All debris flows considered in 

this analysis traveled at least 2 km and were documented by tree-ring analysis. Small debris flows are 

those that were largely in-channel events. Medium debris flows are those that have limited downvalley extent but have some evidence of out-of-bank flow. Large 

debris flows are those that are traceable for several 

kilometers and usually have considerable over-bank 

scour or deposition.
B12 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

This separation allows for the computation of frequency for the different magnitudes by stream. Frequency, by magnitude, was determined for each stream 

by adding the number of tree-ring dates for debris flows 

for each magnitude and dividing by the number of 

years since the oldest dated event.

AGE AND SPATIAL DISTRIBUTION 

OF DEBRIS FLOWS

About 1,100 trees provide evidence for at least 52 

debris flows in 9 basins draining Mount Shasta 

(table 1). Table 1 summarizes the dates of debris-flow 

events and their magnitude in each of the study basins. 

Each stream is described and discussed similarly; the 

general vegetation and geomorphology, dates of debrisflow occurrence, frequency and downvalley distribution of debris flows, and magnitude and frequency of 

debris flows are presented. A site by site description of 

debris-flow activity in the Whitney, Bolam, Mud, and 

Ash Creek basins is detailed in the Appendix.

WHITNEY CREEK

Seven sites of intensive dendrogeomorphic study 

(fig. 3) in order of descending elevation are as follows: 

site 1, just above Whitney Falls; site 2, about 1 km 

above the gorge; site 3, in the gorge; site 4, fan near 

Bolam and confluence with Bolam Creek; site 5, above 

Southern Pacific Railroad; site 6, just below US 97; 

site 7, above Juniper Flat. Dated events range from 

about 1670 to 1985. A debris-flow stratigraphy in the 

gorge shows evidence of debris flows back as far as 

early Holocene times (Osterkamp and others, 1986). 

As will be shown to be true for most streams, discrete 

evidence for all debris flows (small, medium, and large) 

increases in the upstream direction up to the deep 

canyons typically found near tree line and above. The 

lower reaches of the fans tend generally to be dominated by less discrete, fine-grained deposits. Evidence 

of small debris flows in lower reaches, commonly consists of totally in-channel lag deposits barely distinguishable from fluvial deposits. Incised reaches tend to 

be narrow, with most medium to large debris flows 

being largely degradational. Reaches with shallow 

channel beds usually have many discrete overlapping 

debris-flow deposits. Incised reaches usually coincide 

with steep channel gradients, whereas shallow reaches 

coincide with more gentle gradients.

Woody plants readily establish on debris-flow deposits forming initially dense cohorts on the finegrained parts of the surface. These cohorts usually begin growing 1 to 3 years after the debris flow. Trees

growing at the edge of and prior to a debris flow are 

often tilted and scarred as a result of the debris-flow 

passage. Where debris-flow velocities were apparently 

low the trees are relatively undamaged except for depositions at their bases. In general, depositional areas 

tend to have more botanical and geomorphic evidence 

of debris flow than degradational areas such as gorges. 

However, at downstream study sites, where deposits 

are thin and fine-grained, discrete geomorphic forms 

and botanical evidence is hard to find and difficult to 

interpret. This is partly a result of relatively low 

debris-flow velocities and infrequent occurrences and, 

particular to Whitney Creek, the dominance of western 

juniper. This species has obscure ring boundaries, a 

tendency for false and missing rings, and an apparent 

insensitivity to debris-flow depositon. Residents of the 

area, however, indicate that small, in-channel, debris 

flows are frequent under the U.S. 97 bridge (fig. 3).

THE 1985 DEBRIS FLOW

On the evening of July 6, 1985, a medium to large 

debris flow occurred along Whitney Creek. The flow 

was largely confined to the channel from near the toe of 

Whitney Glacier to just below the U.S. 97 bridge, from 

there the flow anastomosed and spread across the 

Whitney-Bolam fan down to Juniper Flat. This flow left 

usually thin bouldery levees along its course that indicated a depth of flow ranging between 5 to 10 m from 

the Falls to U.S. 97. Woody vegetation, mostly shrubs 

and pines, growing near the peak flow height was heavily scarred; virtually all vegetation growing a meter or 

more below the peak flow line was removed by the flow 

from the Falls to U.S. 97. Apparently slower velocities 

spared woody vegetation below U.S. 97 where the flow 

deposited around stems with little immediate damage 

evident, except near the main channel banks. Heights 

of scars on trees and levee placement indicate that this 

1985 event was smaller than the 1935 event, although 

larger than any flow since 1935; botanical evidence of 

the small flows in 1952, 1960, 1974, and 1977 was removed between the Falls and U.S. 97.

EARLIER DEBRIS FLOWS

At least 14 debris flows have left dendrochronologic 

evidence of their passage along Whitney Creek. These 

debris flows are designated alphabetically beginning 

with the oldest. Age and distribution within the basin 

of each event within Whitney Creek basin are shown in 

figure 4.

Two categories of accuracy are inherent in this type 

of tree-ring dating: (1) dates based solely on cohorts of 

trees growing on deposits, and (2) more accurate dates
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B13

TABLE 1. Summary of debris flows on Mount Skasta

[Magnitude and date for all debris flows identified through dendrogeomorphic analysis are shown by basin. A question mark by the magnitude indicates difficulty in magnitude 

determination; date indicated has the confidence limitations as described in text. * is a date based solely on tree age data, t is a year when a debris flow occurred in two or more basins; 

dashes ( ) indicate no debris flows occurred in a particular basin that year ]

Years 

before 

present

0

8

11

14

18

21

23

24

25

27

28

30

33

38

46

48

50

51

57

61

64

66

67

75

77

83

87

99

100

104

112

117

140

145

149

155

181

185

195

200

215

217

245

255

257

260

280

293

302

315

355

405

Year

1985

1977t

1974t

1971t

1967

1964

1962

1961

1960

1958t

1957

1955t

1952f

1947

1939t

1938

1935t

1931t

1928

1924t

1921

1919

1918

1910

1908

1902

1898t

1886

1885

1881t

1873

1868

1845

1840t

1836

1830

1803t

1800*t

1790

1785

1770

1768

1740t

1730

1728t

1725

1705

1693

1683

1670*t

1630

1580

Bolam 

Creek

small

 

small

large

medium

medium

 

medium

large

large

 

Whitney Diller 

Creek Canyon

large 

small 

small 

 

 

 

 

 small

small 

 

 

 

small 

 small

 

 

large small

 

 

 small

medium? 

 

 

small 

 

 

 small

 

 

 

medium? 

 

large 

 

medium 

medium 

 

medium 

 

 

 

 

 

 

medium 

 

 

large 

 

Cascade Panther Mud 

Gulch Creek Creek

 

 

 

 small 

 small

 

 

 

 

small 

 small

 

 

 

 

 

 large

small 

 small large

 

 

 

 medium

 

 

 

 

 medium 

 large

 

 

 

 medium

 

 

 medium 

 medium

 

 

small 

 

 medium

 

 

 

 

 

 medium?

Ash Gravel 

Creek Creek

small 

 

 small

 

 

medium 

 

 

small small

 

 

medium? 

 

medium large

 medium?

medium? 

 

 

 

 

 

 

 medium

large 

 

 

 

small 

 

 

 

 medium

 

medium? 

 

 

 

large 

medium -

large large

medium? 

 

 

 

 large

Inconstance 

Creek

small

small

large

medium?

large

large?

large?
B14 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

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EXPLANATION 1 1

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DEBRIS-FLOW YEARS

FIGURE 4. Age and downvalley distribution of debris flows on Whitney Creek. Dashed lines indicate probable path of debris 

flow, solid lines outline reaches with dendrogeomorphic evidence of flow passage or deposition. Relative magnitude is 

indicated by width between lines. L, M, and S are large, medium and small debris flows, respectively.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B15

based, in addition to tree age, on scars, eccentric ring 

patterns, and suppression and release sequences. The 

events including and prior to 1804 were dated primarily by ages of cohorts of trees growing on discrete deposits. Thus, these dates are approximate and include 

a 5-year maximum time for establishment of trees on 

deposits. The replicated age dates and growth form of 

trees strongly suggest, however, that the date indicated is within 10 years of the actual debris flow. Date 

of debris flows since 1804 may have tree-age evidence 

but is further substantiated by scars or eccentric 

growth patterns. These dates (more recent than 1804) 

are accurate to within 2 years of the debris flow, and 

many of the dates are accurate to the season and year 

of occurrence.

Contrary to other streams on the mountain affected 

by debris flows, most old deposits were found relatively 

high in elevation and recent deposits low in elevation 

(fig. 5). The alluvial fan of the Whitney and Bolam 

drainage (fig. 3) is more deeply incised at its apex and 

spreads farther downslope than other alluvial fans of 

the mountain. Most evidence of debris flows since 1868 

in the upper reaches is degradational, whereas in the 

lower reaches these recent flows, even when small, aggrade quite low on the fan.

The valley cross sections on Whitney Creek (fig. 5) 

show that large debris-flow deposits are generally 

found high in the section and small debris-flow deposits 

are found low in the section. This is true for all studied 

streams on the mountain.

Position in valley cross sections and downvalley distribution suggest that all three magnitudes of debris 

flows (large, medium, and small) have occurred along 

Whitney Creek since 1670. Four large debris flows occurred in 1670, 1840, 1935 and 1985. Medium debris 

flows occurred in 1705, 1790, 1804, 1830, 1868, and 

1919. The debris flows of 1908, 1952, 1960, 1974, and 

1977 were apparently small. The absence of evidence of 

small debris flows prior to 1908 is probably the result 

of scour or deposition by subsequent larger debris 

flows.

The magnitude and frequency relation for Whitney 

Creek is depicted in figure 6. The frequency for all 

datable debris flows on Whitney Creek for the period 

1670 to 1985 is 4.8 per century. Owing to removal of 

evidence of small debris flows their frequency is computed from the earliest date of a small debris flow 

rather than for the entire 3.1-century period. Medium 

debris flows, as defined, have some overbank deposition. Thus, the likelihood of their preservation is increased and their frequency is computed over the 3.1- 

century period. Likewise, frequency of large debris 

flows is computed over the 3.1-century period.

BOLAM CREEK

The four sites of intensive dendrogeomorphic study 

(fig. 3), in order of descending elevation are as follows: 

site 8, upper Bolam near trail switchback; site 9, below 

ford; site 10, above confluence with Whitney Creek; site 

11, on Bolam fan. Evidence of debris flows is widespread along all reaches. Dated events range from 

about 1670 to 1974. No gorge reaches, as described for 

Whitney Creek, were investigated although deeply incised areas occur upstream of the uppermost site. Discrete debris-flow lobes and levees characterize the upper two sites, and they become only slightly less 

distinct at the confluence with Whitney Creek. Apparently, several debris flows left the present Bolam channel and flowed north over the fan above the confluence. 

This may explain a lack of evidence for some debris 

flows below the confluence that are present upstream. 

The documented 1935 event, which occurred on Whitney Creek, also occurred on Bolam Creek. However, the 

channel was considerably less scoured than Whitney 

Creek as a result of the 1935 event. Little deposition 

occurred along Bolam Creek in 1935 as is true on the 

upper reaches of Whitney Creek. The vegetational 

characteristics of Bolam Creek are essentially the 

same as that described for upper Whitney Creek. The 

valley bottoms tend to be broader than those for comparable reaches on Whitney Creek, at least up to site 8 

(fig. 3). Locally extensive recent deposits have spread 

over these bottoms and now support cohorts of Ponderosa pine. Generally, the channel bed of Bolam Creek 

is shallow relative to top banks or debris-flow levees. 

Thus, even relatively small debris flows on Bolam 

Creek may have some overbank deposition.

No less than 10 debris flows have left dendrochronologic evidence of their passage along Bolam Creek. 

These debris flows are designated alphabetically beginning with the oldest. Age and distribution within the 

basin of event on Bolam Creek are shown in figure 7.

In addition to tree ages, most dates are confirmed by 

ring patterns of suppression and release or eccentric 

growth. The accuracy of the dates prior to 1897 is probably within 5 years of the event. Debris flows subsequent to 1897 are further documented by scars from 

corrasion and are accurate to within 2 years of the 

event and in most instances to season of occurrence.

The debris flow of 1670 (A, fig. 7) occurred only at 

site 9 and was dated by a cohort of three Ponderosa 

pines. It is tentative at best that this event is related to 

the 1670 debris-flow terrace in Whitney Gorge. The 

events of 1730, 1785, 1800, and 1845 (B through E, 

fig. 7) left discrete debris-flow lobes or terraces along 

the present Bolam Creek channel. The magnitude and 

frequency relation for Bolam Creek is shown in figure 8.
75 100 125 150 175 200 

TRAVERSE DISTANCE, IN METERS

FIGURE 5. Cross sections of Whitney Creek channel and depositions areas. Note fan development in the lowermost site. Vertical axis is variably exaggerated.

MUD CREEK

Mud Creek has received more attention historically 

than any other stream on Mount Shasta. The documented debris flows of 1924,1925,1926, and 1931 asso-- 

ciated with the breakup of the Konwakiton Glacier, 

prompted scientific research which has persisted to the 

present (Beardsley and Cannon, 1930; Dickson and 

Crocker, 1953; 1954; Glauser, 1967; Hill and Egenhoff, 

1976; Sollins and others, 1983; Hupp, 1984). Most previous work on Mud Creek deals with soil chronoseries. 

No systematic effort to reconstruct debris-flow history 

through tree-ring analysis has been conducted except 

for portions of Hupp (1984) and the present study. The 

Mud Creek basin represents the only basin which poses 

a serious threat to human life and interests because 

Mud Creek flows near the town of McCloud.

Mud Creek flows from the remnants of Konwakiton 

Glacier to the McCloud River (fig. 3). The stream rarely 

reaches the McCloud River, becoming influent on the 

lower reaches of the fan. The major incisement of Mud 

Creek extends farther downslope than any other 

stream on the mountain, which may explain the great

distances debris flows can travel along this stream. The 

length and depth of this incisement suggests a long 

history of debris-flow activity (Osterkamp and others, 

(1986). Mud Creek is probably the most mature 

stream on Mount Shasta and may be more typical of 

streams on other Cascade volcanoes (Crandall and 

others, 1979) than other streams on Mount Shasta.

Mud Creek flows on the humid southeastern face of 

Mount Shasta. Humid conditions favor a relatively diverse tree flora. The principal species along Mud Creek 

include Ponderosa pine, sugar pine, knobcone pine, 

white fir, Douglas fir, red fir, incense cedar, and, locally, California black oak. Douglas and white fir are 

common throughout the studied reaches and are associated with red fir in higher reaches and Ponderosa pine 

on lower reaches.

The deposits from debris flows become increasingly 

finer downslope without an abrupt shift in depositional 

environments that occurs on Ash Creek. Stream gradient and depth of channel incisement into terraces decrease gradually toward the McCloud River. Small and 

medium debris flows are recently less frequent than on
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. BIT

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FIGURE 6. Debris-flow frequency per century by magnitude class on 

Whitney Creek.

other major streams. The near channel terracing as 

described for other streams is apparent, although dominant features particularly below the major incisement 

were developed by debris flows between 1924 and 1931.

The seven sites for intensive dendrogeomorphic 

study (sites 12 through 18, fig. 3) range in elevation 

from 1,850 m to about 1000 m. Sites are numbered in 

order of descending elevation and are from 7.5 km to 

22 km from Konwakiton Glacier. The upper four sites 

down to Mud Creek Dam (fig. 3) are located within the 

deep Mud Creek incisement; the lower three sites are 

on a broad fan.

A complex of terraces at site 13 (fig. 3) has well preserved dendrogeomorphic evidence of eight debris 

flows. The stream is entrenched deeply on the right 

bank and exposes a complex of terraces to a height of 

10 m above the bed (fig. 9). The degradation of the 

channel probably occurred during the historic 1924-31 

events; the lowest terrace is older than the historic 

events. Thus, the flows of 1924-31 were probably still 

bulking through this reach. Site 13 is geomorphically

similar to the Whitney Creek gorge reach. The complex 

of terraces is heavily forested, which allows for fairly 

accurate dating of four debris flows. The terrace complex contains debris-flow surfaces dated from 1630, 

1740, 1881, and 1910 (fig. 9). Levees have been deposited on parts of this complex in 1840, 1924, 1931, 

and 1955.

At least 10 debris flows have left dendrogeomorphic 

evidence of their passages along Mud Creek. These 

flows are designated alphabetically beginning with the 

oldest (about 1630). Age and distribution of these 

events are shown in figure 10. Three (1881, 1924, and 

1931) debris flows were of sufficient magnitude to 

reach the lowest study site on Mud Creek (fig. 10). Each 

event is historically documented (Hill and Egenhoff, 

1976). Several debris flows associated with the breakup 

of Konwakiton Glacier, occurred during the period 

1924 to 1931, but substantial dendrochronological evidence has been recovered only for events in 1924 and 

1931. Events in 1881, 1924, and 1931 were largely degrading (bulking) in the upper three sites (fig. 10).The 

1740 debris flow (B, fig. 10) may have traveled as far as 

site 17; Dickson and Crocker (1953) reported a surface 

in that vicinity of that approximate age. The only small 

debris flows for which there is dendrogeomorphic evidence on Mud Creek occurred after 1931, and are represented largely by small in-channel terraces.

Debris flows grouped into three magnitude categories with frequency per century are shown in figure 11. Distance downslope and overall downvalley 

length of deposition are the best estimators of magnitude. The frequency estimated for small debris flows is 

tentative owing to the short length of record (29 years). 

Frequency estimation for medium and large debris 

flows can be made in greater confidence because the 

dendrogeomorphic record is about 350 years.

In addition to cohort age dates, debris-flow activity 

since 1800 has been documented also by either scars or 

anomalous tree-ring sequences, or both. Debris-flow 

features older than 1840 were dated exclusively by the 

minimum age of cohorts. Except for the period 1924- 

31, debris-flow dates are apparently single events. This 

generalization becomes increasingly tentative with increasing age of a debris flow. Rapid melting of the 

glacier in conjunction with upstream slope failures appears to generate large debris flows clustered in time.

ASH CREEK

Ash Creek, like Whitney and Mud Creeks, received 

proportionately more attention than other studied 

streams owing to its size and frequency of debris-flow 

activity. Unlike Whitney or Mud Creeks, Ash Creek 

has not experienced a large debris flow in this century 

although small and medium debris flows occur fre-
B18 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

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EXPLANATION

 (9) Site number and location

{we) Whitney Creek confluence

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1670

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1730

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1785

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1800

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DEBRIS-FLOW YEARS

FIGURE 7. Age and downvalley distribution of debris flows on Bolam Creek. Dashed lines indicate probable path of 

debris flow, solid lines outline reaches with dendrogeomorphic evidence of flow passage or deposition. Relative 

magnitude is indicated by width between lines. L, M, and S are large, medium and small debris flows, respectively.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B19

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MAGNITUDE AND LENGTH OF RECORD 

(CENTURIES)

FIGURE 8. Debris-flow frequency per century by magnitude class on 

Bolam Creek.

quently. This situation allows detailed investigation of 

small and medium debris flows which have not had 

their associated dendrogeomorphic evidence obliterated or reworked. Additionally, this stream shows how 

these intermediate-sized debris flows tend to fill the 

channel incisement and spread high on the fan in 

reaches where large debris flows typically degrade the 

channel. Data collected from Cold Creek are included 

in this section because Cold Creek is a tributary to 

Ash Creek.

Ash Creek flows nearly due east (fig. 3) and shares 

with Mud Creek the most humid face of Mount Shasta. 

The stream is fed by meltwater from Wintun Glacier 

and streamflow is usually constant during the summer 

at least down to the lowest study site. Streamflow occasionally reaches the McCloud River although much of 

the discharge becomes influent on Coonrod Flat (fig. 3).

The study reaches on Ash Creek can be divided into 

two distinct depositional environments. These environments are separated by the Ash Creek gorge where all 

fluvial and debris-flow activity is constricted to a narrow passage between hard-rock hillslopes. A broad fan 

occurs above the gorge and gradually narrows upslope 

to the major alpine incisement at about 1,830 m in 

elevation. This fan is characterized by stepped, generally coarse-grained terraces and lobes left by debris

flows. The most recent debris-flow deposits are near the 

channel; older deposits lie south of the present channel. 

The left bank in the upper fan reaches is composed 

locally of pyroclastic material that suggests a general 

channel shifting to the north.

The second depositional environment is a broad finegrained fan below the Ash Creek gorge, and, except 

immediately below the gorge, clasts rarely exceed 

10 cm. The channel below the gorge is rarely more than 

2 m below the fan surface. The channel above the gorge 

vertically undulates over the steplike channel deposits 

and can be incised several meters below the fan surface 

near the upstream end of a stepped channel deposit.

Woody plants rapidly establish (within 1 to 5 years) 

on the debris-flow surfaces of Ash Creek. Common tree 

species are Ponderosa pine, sugar pine, Douglas fir, 

white fir, incense cedar, and red fir. Cohorts of these 

species on older deposits facilitate minimum age determination throughout the upper fan. Trees near the 

present channel show damage from several recent debris flows and permit more accurate dating in addition 

to cohort ages.

The seven sites for intensive study on Ash Creek 

range in elevation from about 1,775 m down to about 

1,281 m. These sites are numbered in order of decreasing elevation from site 19 to site 25 (fig. 3). The upper 

five study sites, (19 through 23) are located on the 

upper fan. Site 24 is located in the Ash Creek gorge 

reach. The lowest study site (site 25) is located at an old 

mill site on the lower fan. Most intensive tree-ring 

work was conducted in and above the gorge owing to 

the lack of discrete dendrogeomorphic evidence on the 

lower fan. Most debris flows on the lower fan probably 

occur as slow-moving sheets of fine-grained sediment 

slurries. Furthermore, only the largest flows deposit 

significant amounts of sediment over the lower fan but 

the large flows occur infrequently. As a result, botanical evidence of debris flows is scarce.

At least eight debris flows or debris-flow episodes 

have left dendrogeomorphic evidence of their passage 

along Ash Creek (fig. 12). The debris flows are designated alphabetically beginning with the oldest, the 

Cold Creek episode (1725 to 1768). Debris flows older 

than the Cold Creek episode (A, fig. 12) were not detected by dendrochronological analysis. Thus, the Cold 

Creek episode may have contained the largest debris 

flow on Ash Creek during the past several centuries. 

The 1939 and 1962 debris flows (E and G, fig. 12) may 

have removed in-channel evidence of smaller debris 

flows, those about the size of the 1977 debris flow (H, 

fig. 12).

The debris flows were divided into three magnitude 

categories as described for Whitney Creek. However, 

owing to relatively shallow channel incisement even at 

the highest study site, small debris flows may overtop
DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

I I I

MUD CREEK 

3 km above dam

1740

80 100 120 140 

TRAVERSE DISTANCE, IN METERS

FIGURE 9. Cross section of Mud Creek 3 km above dam. Multiple debris-flow terracing and dates are shown. Note lack of evidence of historic 

1924 to 1931 debris flows (bulking in this reach). Landslides on right bank may contribute sediment to debris flows.

the bank in some locations. As for most Mount Shasta 

streams affected by debris flows, distance downslope of 

overbank deposition seems to be the best estimator of 

debris flow magnitude on Ash Creek. Only large debris 

flows (A and D, fig. 12) are capable of substantial deposition on the lower fan. These trends support the generalization that large debris flows degrade and bulk up 

high on the mountain, whereas smaller debris flows 

tend to aggrade high on the mountain and are largely 

in-channel events farther downslope (fig. 12). Thus, 

small debris flows fill channels degraded by larger debris flows, which suggests an overall cyclic process of 

channel filling and scouring controlled by the magnitude and frequency of debris flows. There seems to be 

a directional trend during the last several decades for 

medium and small events to build the fan in the upstream direction.

The frequency per century of debris flows in Ash 

Creek is shown in figure 13. The substantial debris 

flows of 1939 and 1962 (E and G, fig. 12) probably 

obscure evidence of most small flows prior to 1939. 

Thus, only a conservative estimate of small debris-flow

frequency may be made. At least three small flows 

have occurred since 1873. Medium and large debrisflow frequency (fig. 13) is computed for the entire dendrochronologic length of record (260 years).

Each proposed date of a debris flow on Ash Creek is 

substantiated by cohort age and either ring-pattern 

anomalies or scars or both. Thus, accuracy prior to 1898 

is probably to within 3 years of the event and to within 

1 year from 1898 to present. It should be noted, however, that the Cold Creek episode is composed of a 

series of at least three major and numerous smaller 

events. The anastomosing and reworking nature of 

these flows over the upper fan makes further dating 

difficult. The major debris flows probably occurred 

about 1728, 1747, and 1768. There is some dendrochronologic evidence of a small event on the upper 

fan about 2 years prior to the 1939 debris flow. The 

remaining debris-flow dates are probably single 

events. The tendency for debris flows to cluster in time 

may be related to periods of heightened bankslope instability in alpine reaches of Mount Shasta streams. 

Bankslope instability in conjunction with anomalously
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B21

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EXPLANATION

~~ (12) Site number and location

1 1 1 1

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1840 1881 1910 1924 1931 1955 1964 

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DEBRIS-FLOW YEARS

FIGURE 10. Age and downvalley distribution of debris flows on Mud Creek. Dashed lines indicate 

probable path of debris flow, solid lines outline reaches with dendrogeomorphic evidence of 

flow passage or deposition. Relative magnitude is indicated by width between lines. L, M, and 

S are large, medium and small debris flows, respectively.
B22 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

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MAGNITUDE AND LENGTH OF RECORD 

(CENTURIES)

FIGURE 11. Debris-flow frequency per century by magnitude class 

on Mud Creek.

high summer temperatures appears to be correlated 

with debris-flow activity (Osterkamp and others, 

(1986).

The upper site (19, fig. 3) is a good example of the 

different types of deposition that can result from the 

viscous nature of debris flows. The 1939 event left the 

channel at site 19 and scarred trees on the fan surface 

for hundreds of meters downslope and adjacent to the 

channel; most deposition from this event occurred farther downstream from site 19. A plan view of site 19 is 

shown in figure 14. The debris flows of 1962 and 1977 

were depositional throughout the site, leaving distinct 

levees in the upper part and spreading into a broad 

sheetlike lobe (fig. 14). The 1962 event was substantially larger than the 1977 event and it deposited lobate sheets farther downslope and over a broader area 

(fig. 14). The channel is perched on the surface of the 

1977 deposit (fig. 15) before it shifts to the right side of 

the 1962 surface downslope. Perched channels are indicative of recent events, where levees confine the 

channel to the higher central part of the deposit 

(fig. 15). Typical terracing of debris flows occurs about 

2 km downstream near Military Pass Road (fig. 3). The 

incisement abruptly becomes deeper off the 1962 surface. Here the typical terracing (fig. 16) begins and 

continues to the gorge. The 1939 event deposited an 

intermittent sheet of fine-grained material on the top 

bank near the channel. Roots growing before 1939 

show the thickness of the 1939 deposit (fig. 17). Evidence from tree rings was determined for events in 

1898,1873, and about 1800. The 1898 event left a continuous sheet of fine-grained material at the top bank 

and immediately below the 1939 deposit.

COLD CREEK, SITES 26, 27, AND 28

Cold Creek (fig. 3) has been included in the Ash 

Creek section because it is a tributary to Ash Creek 

and has no direct glacial connection. Additionally, 

prior to the Cold Creek episode this stream probably 

joined Ash Creek substantially farther upstream. All 

debris-flow activity on Cold Creek is directly related to 

flows originating in the Ash Creek basin and discharges from Wintun Glacier.

Owing to similarity among the three sites on Cold 

Creek this discussion applies to all three sites. The 

study sites are evenly spaced between 1,700 m and 

1,460 m in elevation. The right bank of Cold Creek is 

composed of pyroclastics through most of its reach. The 

left bank is composed of deposits from the Cold Creek 

episode. Tree-ring evidence suggests that the greatest 

periods of debris-flow activity during the Cold Creek 

episode occurred in 1728 and in the late 1740's. The 

1898 debris flow apparently had a small arm of deposition along the upper Cold Creek site. Red staining in 

the rings of a few riparian trees suggests that floods 

may have occurred in conjunction with the 1962 and 

1977 debris flows on Ash Creek (red staining in rings 

produced during flood years has been observed in trees 

affected by documented floods). Thus, recent debris 

flows rarely affect the Cold Creek channel but concomitant flooding may occur.

GRAVEL CREEK

Gravel Creek flows on the northeast face of Mount 

Shasta draining the Hotlum Glacier. Four sites of dendrogeomorphic study were established along Gravel 

Creek (fig. 3). These sites were located at the intersections of the stream with road crossings. The uppermost 

site (site 29) is located at an elevation of about 2,135 m 

(fig. 3) and is the site of most intensive debris-flow 

dating. Sites 30, 31, and 32 are located progressively 

downstream (fig. 3) and were visited briefly to determine the downvalley extent of major debris flows identified at site 29. The lowermost site (site 32) is located 

in a saddle situated among Mount Shasta peak, the 

Whaleback, and Ash Creek Butte (fig. 3). Site 32 is
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B23

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EXPLANATION

(ft) Site number and location

A B C D E F

1725-68 1800 1873 1898 1939 1958

L M S L M S

G

1962

M

H

1977

S

DEBRIS-FLOW YEARS

FIGURE 12. Age and downvalley distribution of debris flows on Ash Creek. Dashed lines indicate probable 

path of debris flow, solid lines outline reaches with dendrogeomorphic evidence of flow passage or 

deposition. Relative magnitude is indicated by width between lines. L, M, and S are large, medium and 

small debris flows, respectively.
B24 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

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MAGNITUDE AND LENGTH OF RECORD 

(CENTURIES)

FIGURE 13. Debris-flow frequency per century by magnitude class 

on Ash Creek.

highly aggradational, dominated by fine-grained sediments delivered by Gravel Creek which becomes influent in this reach.

Generally, there is much evidence of debris-flow activity along the upper reaches of Gravel Creek. In the 

vicinity of site 29, the stream has a distinct incisement 

with an anastomosing series of debris-flow levels on the 

left side of the valley. Since about 1580, the channel 

has been shifting from northwest to southeast (left to 

right). This prevailing directional shift has preserved 

depositional features of at least seven debris flows on 

the left side of the valley while cutting into older pyroclastic deposits on the right bank. In cross section, the 

channel at site 29 is perched higher than some of the 

area affected by debris flows on the left side of the 

valley. Thus, while shifting over the past four centuries 

the stream has become increasingly aggradational at 

site 29.

Gravel Creek exemplifies the trend found on most of 

the streams for discrete surficial dendrogeomorphic evAsh Creek, site 19

Haul

200 400 600 FEET

\ I I 

100 200 300 METERS

FIGURE 14. Plan view of upper Ash Creek. Age and locations of three recent debris flows (1939,1962, and 1977) are shown. Locations of cross

sections A-A' and B-B' are shown in figure 15.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B25

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upper crossing

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Ash Creek, on 1962 

debris flow

50 100 150 200 250 300 350 400 450 500 550 600 650 700

TRAVERSE DISTANCE, IN METERS

FIGURE 15. Two cross sections on upper Ash Creek. Note perched condition of channel on the recent 1977 deposit. Cross section on 1962 

deposit with areas of lobes and scour is shown at bottom of figure; note perched condition of channel, washes (scoured areas) to left are 

possible sites of stream capture.

idence of debris flows to increase in the upstream direction. Debris-flow deposits are thin below site 29 and are 

subject to fluvial reworking. Furthermore, only large 

debris flows appear to proceed downslope as far as site 

32 and these may represent debris-flow runouts finegrained flood deposits associated with upstream debris 

flows.

The forests along Gravel Creek are dense and diverse 

reflecting the more humid conditions of the eastern 

side of the mountain. Ponderosa pine, prevalent on the 

northwest face, is present only sporadically. Western 

white pine, Douglas fir, lodgepole pine, and red fir are 

the prevalent tree species; the two latter species are 

particularly common at higher elevations. Red fir is the 

dominant species at site 29.

SITE 29

This site (fig. 3) is located just downstream from the 

area where debris flows have breached the channel incisement. Above this area debris flows are contained 

entirely by steep pyroclastic banks. Site 29 thus marks

the beginning of the Gravel Creek debris fan which 

rapidly spreads laterally with decreasing gradient toward the saddle. The area of intensive study includes a 

reach about 0.75 km above the road crossing and an 

equal distance below.

The surface of the fan at this site is characterized by 

anastomosing and overlapping discrete debris-flow deposits and scour areas. The oldest debris-flow features 

are on the left side of the fan and generally decrease in 

age toward the right bank which is composed of pyroclastic deposits. Many of the deposits are coarse 

grained (boulders up to 1 m) and stand in high relief (up 

to 5 m) to adjacent scoured areas.

Site 29 supports many trees with damage from 

debris-flow passage. Many of the debris-flow lobes support cohorts of trees on the fine-grained interior lobe 

surface (fig. 18). Some of these lobes have dense cohorts 

of red fir that are only a few meters high but are hundreds of years old. More recent lobes came to rest 

against large trees which were scarred at time of impact and thus allow for accurate determination of 

debris-flow dates.
B26 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

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ASH CREEK (Not to scale)

FIGURE 16. Terracing by debris flows on Ash Creek near Military Pass Road.

Evidence of at least seven debris flows was recovered 

from site 29 (table 2). The earliest dated event occurred 

about 1580 and is preserved as a downvalley series of 

weathered lobes on the left side of the fan. Subsequent 

events occurred to the right of these surfaces and generally increase in elevation (in cross section) toward 

the present channel (fig. 19). Subsequent debris-flow 

events occurred jn or about 1728,1836,1902,1937-39, 

1958-59, and 1971. The two most recent events were 

apparently small flows confined largely to the channel, 

which deposited coarse levees at the channel edge. The 

events in 1728 and 1937-39 were large debris flows 

approaching the 1580 event in magnitude. These two 

large events spread over parts of the fan surface scouring older deposits in places and depositing lobes which 

now stand in high relief (fig. 19). The remaining dated 

events (1836 and 1902) apparently were medium debris 

flows that breached the channel in only a few places. 

However, both events left discrete lobes over the 1728 

surface that were not reworked by the 1937 and 1939 

events. The events of 1937-39 and, to a lesser degree, 

1958-59, appear to be a cluster of debris flows. This

tendency for two or more debris flows to occur within a 

few years of each other has been observed on several of 

the glacial-headed streams. Evidence for events in 

1937 and 1939 suggests that the debris flows are two 

distinct events during the 3-year period.

The trend for small events to be preserved only if 

they are recent is evident in table 2. Evidence of earlier 

small events was most likely obliterated by the 1937- 

39 events, which precludes accurate frequency interpretations for small events on Gravel Creek. However, 

a fairly reliable frequency estimate may be calculated 

for combined medium and large events. Events such as 

that of 1902 (medium) and larger occur on Gravel 

Creek about once every 80 years. Large debris flows 

probably occur less frequently; small events are substantially more frequent, tentatively about once every 

13 years. Relative to other mountain streams this is an 

active basin for debris flows. However, flows have 

limited downvalley extent relative to other streams 

perhaps owing to an abrupt shift in gradient and the 

lack of an entraining incisement below 2,135 m in elevation.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B27

FIGURE 17. View of Ash Creek channel banks above Military Pass Road. Sediment over exposed root zone (arrow) was deposited during 

the 939 debris flow. This deposit varies in thickness (up to 1.5 m) through sites 20 and 21.

SITES 30, 31, AND 32

These sites (fig. 3) are almost entirely dominated by 

fine-grained deposits, most of which have been reworked through fluvial activity. The channel at the 

lower two sites (31 and 32) is shallow and usually less 

than a meter below the broad alluvial fan. These sites 

have undergone substantial aggradation of finegrained sediments. Typical lobes and levees from debris flows is lacking, instead runoutlike deposits occur 

and may be associated with debris-flow activity upstream.

The event of 1902 is the oldest of the seven dated 

events below site 29. Eccentric growth beginning in 

1902 was found in a specimen at site 31. Scars on a few 

trees at sites 30 and 31 document the debris flow in 

1939, which suggests that the 1939 event was the 

larger of the two events in 1937-39. One tree with 

eccentric growth beginning in 1959 and a tree scarred 

in 1971 are the only evidence of small flows at site 31.

Several partially buried trunks at site 32 have an average minimum age of 26 years (possibly dating the 1958 

flow). These young trees are the only datable dendrochronologic evidence of depositional activity at site 

32. Fine-grained sediments up to 1.5 m thick occur 

above the root collars of the young trees at site 32; thus 

an aggradation rate of about 60 cm per year since 1958 

is indicated.

INCONSTANCE CREEK

Inconstance Creek was studied at only one site 

(site 33, fig. 3) at an elevation of about 2,300 m. This 

site is characterized by a fairly deeply incised channel 

with a narrow terrace and an overlying series of debrisflow deposits on the right bank. Vegetation on the terrace and right bank shows the effects of periodic debris 

flows through scars, buried trunks, and ring patterns.

A stand of western white pines dates the terrace surface to about 1680. Subsequent eccentric growth pat-
B28 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

FIGURE 18. Sapling cohort on debris-flow lobe near site 29 on Gravel Creek. Saplings date a debris flow in 1939.

TABLE 2. Summary of debris flows and magnitudes on Gravel Creek 

in the vicinity of site 29

[Asterisk indicates geomorphic evidence of the debris flow was also found at lower sites. S, 

M, and L are small, medium, and large debris flows, respectively.]

Date

1580

1728

1836

1902*

1937-39*

1958-59*

1971*

Magnitude

S M

X

X

X

X

L

X

X

X

terns suggest debris-flow passage in 1693, 1728, and 

1881. Coarse levees which dominate the channelward 

terrace edge were left by a debris flow in 1918 as dated 

from numerous scars and eccentric growth patterns 

(fig. 20). Boulders left as levees by the 1918 event 

ranged in size from 0.25 m to 1.5 m. A few surviving

white pines below the 1918 levees have scars from a 

smaller in-channel debris flow in 1939 which formed 

levees inside the 1918 levees. Small paired terraces 

adjacent to the channel have a minimum age of about 

20 years as dated from a cohort of white pine saplings. 

A red intra-ring stain (possibly a layer of crushed cells) 

in these saplings suggests a flood event occurred in 

1971. The well preserved nature of relatively old 

debris-flow deposits at site 33 suggests that debris 

flows are not as frequent as on other glacier headed 

streams of Mount Shasta. Channel, levees, and old terraces are shown in figure 21. Dendrogeomorphic evidence suggests that events in the late 1600's partly 

filled the channel incisement. Subsequent events have 

largely degraded the site as suggested by the lack of 

deposits on the terrace since about 1680 except for the 

1918 levees. Events in the last 250 years, including the 

undoubtedly large debris flow in 1918, have bulked up 

at site 33 and were depositional farther downstream. 

Only small debris flows aggrade at this site.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B29

2149

O)

CC 2147

LU

GRAVEL CREEK

2145

2135

10 20 30 40 50 60 70

TRAVERSE DISTANCE, IN METERS

80 90 100 110

FIGURE 19. Cross section of Gravel Creek near site 29. Note progressively increasing elevation of deposits and decreasing age of deposits

toward the left bank.

Inconstance Creek, 

scar in 1918 with 

subsequent eccentric 

gro

FIGURE 20. Cross section of western white pine affected by debris 

flow on Inconstance Creek. Tree was scarred and tilted in 1918 

resulting in eccentric growth after 1918.

Debris flows of all magnitudes are relatively infrequent on Inconstance Creek. Tree-ring data suggest 

that debris flows of any magnitude occur here only once 

every 38 years. Large debris flows occur substantially 

less frequently than once every 38 years, probably 

about once per century.

NONGLACIAL STREAMS

Panther Creek, Cascade Gulch, and Diller Canyon 

(fig. 3) are streams which are not presently draining 

glaciers. These streams have dendrogeomorphic evidence of debris flows; however, activity is much less 

than on streams previously discussed (table 1). The 

lack of a direct glacial connection probably precludes 

relatively frequent debris flows; and those that have 

occurred usually have been small.

PANTHER CREEK

Panther Creek flows on the south face of Mount 

Shasta. It is speculated that this stream may have had 

some connection to the Konwakiton Glacier in the past 

(J. Thornton, U.S. Geological Survey oral commun., 

1982). Studies were made at only one site (site 34, 

fig. 3) near the old Mount Shasta-McCloud Road; elevation is about 1,685 m.
B30 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

FIGURE 21. View of Inconstance Creek near site 33. Note levees and terrace on left.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B31

Dendrogeomorphic evidence indicates that four debris flows occurred since about 1804. Relatively small 

debris-flow terraces occur above the road. The two 

largest debris flows were dated to about 1804 and 1885 

from cohorts of Douglas fir and incense cedar. Small 

in-channel terraces were deposited in 1924 and 1967, 

as dated from scars and anomalous tree-ring sequences.

CASCADE GULCH

Cascade Gulch is located on the southwest flank of 

Mount Shasta. (fig. 3). The stream within Cascade 

Gulch flows intermittently even during summer 

months and becomes totally influent a few kilometers 

above the city of Mount Shasta. Dendrogeomorphic evidence for debris flows was found at one site (site 35, 

fig. 3) above the intersection of the stream and Everitt 

Memorial Highway. Three deposits left by small debris 

flows were dated about 1770, 1928, and 1957.

DILLER CANYON

Diller Canyon lies on the west face of Mount Shasta, 

more specifically on the Shastina peak (fig. 3), and the 

stream within Diller Canyon becomes influent a few 

kilometers above Weed. There is geomorphic evidence 

of a historic glacier on Shastina, although Diller 

Canyon presently has no glacial connection. The relatively deeply incised canyon suggests sediment discharges were previously higher, possibly due to debris 

flows, but there have been no recent large flows datable 

by tree-ring sampling.

Diller Canyon was investigated at two sites for dendrogeomorphic evidence of debris flows. The highest 

site (site 36, fig. 3) is located at an elevation of about 

2,300 m within the major incisement. One incised terrace was deposited in 1935 and may be meteorologically related to activity on Whitney Creek in that same 

year. Other older terraces were apparent but were not 

dated. The other site on this stream (site 37, fig. 3) is 

located on a fan developed in the lower reaches, at an 

elevation of about 1,500 m. Dendrogeomorphic evidence suggests that four small debris flows occurred in 

about 1886, 1921, 1947, and 1961. The 1935 event at 

the higher site did not proceed as far downslope as 

site 37.

DISCUSSION

Some coincidence of debris-flow dates is evident 

(table 1). Of the 52 events listed, 30 percent occurred 

ion two or more streams in a given year; in 1728 and 

1939 debris flows occurred on three streams. This 

would suggest a relation between weather patterns affecting the entire mountain and debris-flow activity.

Osterkamp and others (1986) have suggested that high 

summer temperatures are related to debris-flow activity for the period for which temperature data are available. Botanical evidence reveals most scarring from debris flows is within the interval of seasonal growth and, 

hence, formed during summer months. This observation supports the contention that high summer temperatures may, in part, initiate debris flows. It is also 

likely that local summer storms over individual basins 

may be responsible for some debris flows, particularly 

small events.

Debris-flow frequency since 1580 is shown in figure 22. It is apparent that small debris flows (shown as 

dashed vertical lines, fig. 22) are more easily detected 

if they occurred recently. Only 3 of 18 are more than 

100 years old. The frequency of medium and large 

events also decreases with age (fig. 22), which is partly 

an artifact of tree-ring dating, because subsequent 

events remove evidence of previous events. However, 

Osterkamp and others (1986) present other lines of 

evidence that indicates heightened debris-flow activity 

in the last few centuries. Four periods of relatively high 

debris-flow frequency are apparent (fig. 22): 

(1) between 1898 and 1940, (2) between 1830 and 1845, 

(3) between 1780 and 1805, and (4) the Cold Creek 

episode from 1725 to 1770. The 1700's experienced 

heightened debris-flow activity relative to the 1800's 

and the last half of the present century (fig. 22), which 

may be related to the "little ice age" when anomalously 

large amounts of ice and snow accumulated.

The interval of years between debris flows of any 

magnitude on glacial streams has a mean value of 6.24 

years. Years with more than one medium to large debris flow seem to be an indicator of periods of heightened debris-flow frequency rather than long strings of 

single-event years (fig. 22). This observation supports 

the premise that debris flows occur in clusters over a 

period of not more than a few decades. The mean gap 

between multiple-event years is 41.4 years (n=7, 

s=±26.8). Relative debris-flow activity by basin may 

be estimated by calculating the mean age of small debris flows (fig. 23). Evidence of small debris flows is 

highly susceptible to obliteration by medium and large 

flows. Thus, the mean age of small debris flows should 

reflect the level of debris flow activity in a basin. 

Basins with recent evidence of small flows are probably 

active basins; conversely, substantial evidence of old 

small flows should indicate relatively low debris-flow 

activity. Geomorphic observations by Osterkamp and 

others (1986) suggest that Gravel Creek is one of the 

most active basins and that Inconstance Creek is the 

least active basin. These observations are supported by 

the calculated mean age of small flows depicted in figure 23.
B32

7 

6

FLOWS

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DEBRIS-FLOW ACTIVITY

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T

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AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

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1

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80 70 60 50 40 30 20 10 00 90 80 70 60 50 40 30 20 10 00 90 80 70 60 50 40 30 20 10 00 90 80 70 60 50 40 30 20 10 00 90 80 70 60 

1900's «-J 1800's 1700's 1600's 1500's

YEAR

FIGURE 22. Age and frequency of debris flows on Mount Shasta back to 1580, all dates from botanical evidence. Medium and large debris 

flows are indicated with solid lines, small flows with dashed lines. Note lack of evidence for small debris flows with increasing age.

o

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w 0.008 

0.007 

0.006 

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19.50

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Grauel Mud Whitney Bolam Ash Inconstance

Creek Creek Creek Creek Creek Creek

FIGURE 23. Debris-flow activity by basin. Calculated as mean age of 

small debris flows, shown as reciprocal on vertical axis (log scale). 

Actual mean value shown at top of bar.

The glacial basins, in order of decreasing debris-flow 

activity, are Gravel Creek, Mud Creek, Whitney 

Creek, Bolam Creek, Ash Creek, and Inconstance 

Creek (fig. 23). Gravel Creek may be currently in a 

heightened phase of activity (Osterkamp and others, 

1986). The recent breakup of the Konwakiton Glacier

may explain the high degree of activity on Mud Creek. 

The order-of-magnitude decrease in activity in the Inconstance Creek basin (fig. 23) may result from a small 

basin area, shallow channel incision in alpine areas 

(Osterkamp and others, 1986), and perhaps an inactive headwater glacier.

The evidence indicates a cyclic nature of sediment 

movement through glacially fed basins. Apparently 

during periods between major debris flows medium and 

small debris flows allow for storage of sediment relatively high on the mountain. These sediments are 

stored as lobes and terraces within the active channel 

incisement. The middle and upper reaches of Ash 

Creek provide a good example of the stepped channel 

fill associated with a relatively long period since a 

major event. Whereas, the middle and upper reaches of 

Whitney Creek reflect the scouring nature of large 

events. The cycle of channel filling and scour may be 

imbedded in a larger cycle of periods of heightened 

debris-flow activity and relatively quiescent periods. 

Examples of heightened periods of activity are the 

1920's and early 1930's on Mud Creek and the Cold 

Creek Episode on Ash Creek. Inconstance Creek may 

represent a basin currently in a period of quiescense as 

evidenced by the good preservation of old medium and 

small debris flows. Conversely, Gravel Creek may be 

currently in a heightened period of activity, suggested 

by evidence of recent numerous small and medium debris flows.
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B33

Analysis of dendrogeomorphic evidence has allowed 

for the development of debris-flow histories for the 

streams draining Mount Shasta, Calif. Debris flows 

have been dated over a 400-year period back to 1580. 

No other methods are available which provide the degree of accuracy in the development of debris-flow histories beyond times of historic documentation as afforded through tree-ring analyses. Dates of debris flows 

and their downvalley distribution from botanical evidence when combined with geomorphic evidence provide a means for better estimation of magnitude and 

frequency of debris flows over a several hundred year 

period.

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Blodgett, J.C., and Bureau, J., in press, Hydrologic and volcanic 

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Butler, David R., 1979, Snow avalanche path terrain and vegetion, 

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Christiansen, R.L., 1982, Volcanic hazard potential in the California 

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Cooke, W.B., 1940, Flora of Mount Shasta: The American Midland 

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Costa, John E., 1984, Physical geomorphology of debris flows: in J.E. 

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Costa, John E., and Jarrett, R.D., 1981, Debris flows in small mountain stream channels of Colorado and their hydrologic implications: Bulletin of the Association of Engineering Geologists, 

v. XVIII, no. 3, p. 309-322.

Crandell, D.R., 1971, Postglacial lahars from Mount Ranier Volcano, 

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Crandell, D.R., Mullineaux, D.R., and Miller, C.D., 1979, Volcanic 

hazards studies in the Cascade Range of the western United 

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p. 195-219.

Curry, R.R., 1966, Observation of alpine mudflows in the Ten Mile 

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v. 77, p. 771-776.

Dickson, B.A., and Crocker, R.L., 1953, A chronosequence of soils and 

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eco-system investigated and features of the plant succession: 

Journal of Soil Science, v. 4, no. 2, p. 123-141.

 1954, A chronosequence of soils and vegetation near Mount 

Shasta, California; III. Source properties of the mineral soils: 

Journal of Soil Science v. 5, no. 2, p. 173-191.

Flaccus, E., 1959, Revegetation of landslides in the White Mountains 

of New Hampshire: Ecology, v. 40, p. 692-703.

Fritts, J.C., 1976, Tree rings and climate: Academic Press, London, 

576 p.

Gardner, J.S., 1982, Alpine mass-wasting in contemporary time: 

some examples from the Canadian Rocky Mountains, in Thorn, 

C.E. (ed.) Space and Time in Geomorphology, George, Alien, and 

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Glauser, Robert, 1967, The ecosystem approach to the study of the 

Mount Shasta mudflows: Ph.D. Thesis, University of California, 

Berkeley, CA.

Hack, J.T., 1965, Geomorphology of the Shenandoah Valley, Virginia 

and West Virginia, and the origin of the residual ore deposits: 

U.S. Geological Survey Professional Paper 484, p. 84.

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Helley, E.J., and LaMarche, V.C., Jr., 1973, Historic flood information for northern California streams from geological and botanical evidence: U.S. Geological Survey Professional Paper 485-E, 

16 p.

Hill, Mary, and Egenhoff, E.L., 1976, A California Jokulhlaup: California Geology, July 1976, p. 154-158.

Hupp, C.R., 1983, Geo-botanical evidence of Late Quaternary mass 

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 1984, Dendrogeomorphic evidence of debris flow frequency 

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Hupp, C.R., and Sigafoos, R.S., 1982, Plant growth and block-field 

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budgets and routing in forested drainage basins: U.S. Forest 

Service General Technical Report PNW-141, p. 78-85.

Jackson, Lionel E., 1977, Dating and recurrence frequency of prehistoric mudflows near Big Sur, Monterey County, California: Journal of Research of the U.S. Geological Survey, v. 5, no. 1, p. 17- 

32.

Janda, R.J., Scott, K.M., Nolan, K.M., and Martinson, H.A., 1981, 

Lahar movement, effects, and deposits in the 1980 eruptions of 

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Jenny, Hans, 1980, The soil source resource, origin and behavior: 

New York, Springer-Verlang, p. 215-217.

Kochel, R.C., Johnson, R.A., and Valastro, S., 1982, Repeated 

episodes of Holocene debris avalanching in central Virginia: 

Geological Society of America, Abstracts Programs, v. 14, no. 12, 

p. 31.

LaMarche, V.C., Jr., 1968, Rates of slope degradation as determined 

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Langenheim, Jean H., 1956, Plant succession on a subapline earthflow in Colorado: Ecology, v. 37, no. 2, p. 301-317.

Little, E.L., Jr., 1979, Checklist of United States trees (native and 

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32.

Meier, M.F., and Tangborn, W.V., 1965, Net budget and flow of South 

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Miles, D.W.R., Swanson, F.J., and Youngberg, C.R., 1984, Effects of 

landslide erosion on subsequent Douglas fir growth and stocking
B34 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

levels in the western Cascades, Oregon: Soil Science Society 

America Journal v. 48, p. 667-671.

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Mount St. Helens, Washington: Geological Society of America 

Bulletin., v. 73, p. 855-870.

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Osterkamp, W.R., Hupp, C.R., and Blodgett, J.C., 1986, Magnitude 

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N.W.T. Part I: Using tree damage to date landslides, ice jamming, and flooding, in Hydrologic aspects of Northern Pipe Development (Task Force on Northern Oil Development), p. 313- 

464.

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 1980b, Erosion and deposition by debris flows at Mount 

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Mathematisch-Physikalishe Klasse, Nr. 13, p. 197-210.

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und Klima in der dendrochronologie: Verlag, Paul, und Haupt, 

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movement of Table Cliffs Plateau, Utah: Quaternary Research 

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stabilization of alpine glacial deposits and establishment of tree 

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in the flood of December 1964 on Coffee Creek, Trinity County, 

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Geological Survey Professional Paper, 1296, 42 p.
APPENDIX: DETAILED SITE DESCRIPTIONS

WHITNEY CREEK

SITE 1, ABOVE WHITNEY FALLS

Site 1 (fig. 3) is largely degradational in character. 

The historic 1935 debris flow scarred several trees 

within the channel incisement but left few deposits. 

One older debris-flow levee just below the top bank was 

dated to about 1868. All overbank deposits were older 

than the existing trees. The predominance of pyroclastics near the channel incisement suggests that few recent debris flows have overtopped the banks at this 

site. The absence of scars or tilts after 1935 within the 

channel incisement suggests that nothing larger than 

the 1935 event has since passed through this site. The 

1935 event was largely degradational throughout the 

upper reaches at least past the gorge. A recent event, 

1985, left a debris line just below the 1935 levees, suggesting a magnitude slightly smaller than the 1935 

event.

SITE 2, ABOVE THE GORGE

Site 2 (fig. 3) is a relatively narrow-bottom well 

within the major channel incisement. The channel itself is deeply incised into the bottom, lending a terraced 

appearance. The surface of this terrace is characterized 

by many overlapping and often steep, discrete debrisflow lobes. The oldest and farthest downvalley event on 

this terrace occurred about 1670. This flow may make 

up a considerable volume of the terrace with more recent, small debris flows deposited over the 1670 surface. The 1670 debris flow may have sufficiently filled 

the channel to allow for debris from several flows of 

smaller magnitude to be deposited on the terrace. 

Three debris-flow lobes on this surface were dated to 

about 1705, 1790, and 1804. The 1804 debris flow was 

at least partly responsible for a narrow, lower terrace 

on the left bank. At least two debris flows between 1830 

and 1840 were of sufficient magnitude to scour much of 

the left bank and a back channel on the right side of the 

terrace. Two remnants of debris-flow levees inside the 

channel incisement of the main terrace were dated to 

about 1868 and 1981. The 1935 debris flow was entirely 

degradational in this area, leaving only scars on the 

few trees growing inside the channel just below the 

terrace. Considerable bulking of the 1935 event may 

have occurred in this reach and the gorge is suggested 

by the absence of trees older than 1935 more than 2 m

below the terrace edge. The channel in this reach and 

the gorge are as much as 10 m below the terrace edge. 

A recent datable event occurred about 1960 and appeared as a locally present, relatively low, small inchannel terrace. The 1960 evidence was removed by the 

flow in 1985.

SITE 3, IN THE GORGE

Site 3 (fig. 3) is partly described in the previous section (site 2). The reach is characterized by a deep, wide 

channel incisement with a substantial terrace 3/4 of the 

way below the top of the incisement. The channel is 

deeply incised into this terrace on the left bank. The 

surface of this terrace is largely composed of the 1670 

debris flow with a back channel on the right side 

formed during the passage of the 1830-1840 debris 

flows. A lobe of the 1841 debris flow occurs on the upper 

end of the 1670 terrace. Scarring of trees at the left 

edge of the terrace occurred in 1868 and 1935. No trees 

grow more than 2 m below the left terrace edge, which 

provides further support of the degradational nature of 

debris flows in this and upstream reaches since the mid 

1800's. A flow in 1985 left a thin boulder line a few 

meters below the 1670 terrace.

SITE 4, FAN NEAR CONFLUENCE WITH BOLAM CREEK

Site 4 (fig. 3) covers the upper fan reaches of Whitney 

Creek. Generally, the stream is not as deeply intrenched as the reaches above. Pyroclastic deposits 

occur near the top bank with stratified debris-flow deposits nearest the channel. Some evidence of 

anabranching occurs near bends in the stream. Trees at 

site 4 and below are sparse probably owing to fire and 

lumbering. Two terracelike features are locally exposed along this reach: a lower one with young small 

trees and higher one with scattered older trees. Depositional patterns are complex and discontinuous along 

the reach. Botanical evidence exists for only relatively 

recent debris flows in about 1840, 1868, and 1908. 

Scars dating the 1935 event were found on some of the 

older trees as well as scars between 1952 and 1954. As 

will be shown for other streams, surficial geomorphic 

and botanical evidence becomes more difficult to interpret downvalley.

B35
B36 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

SITE 5, ABOVE SOUTHERN PACIFIC RAILROAD

Site 5 (fig. 3) is similar to that described above 

(site 4) in its geomorphic and botanical characteristics. 

A low terrace is common along the reach and higher 

terracing locally common. Few trees grow along 

Whitney Creek, although botanical evidence was found 

for flows between 1918 and 1921, and in 1935, 1950, 

between 1958 and 1962, and 1985.

SITE 6, JUST BELOW U.S. 97

Site 6 (fig. 3) is characterized by a shallow channel, 

rarely more than 2 m below topbank. It is apparent 

that many hydrologic events (floods, mudflows, and debris flows) begin to spread and anastomose from site 6 

downslope as indicated by many shallow diversion 

channels. Except in the immediate vicinity of the main 

channel, the deposits are very fine grain relative to 

those upstream. Ponderosa and Jeffrey pines, which 

compose nearly all of the botanical evidence upstream 

(except alpine species above the falls), give way to increasing dominance of juniper downstream. The dendrochronologic limitations of juniper have been noted 

previously. Isolated stands of pines near the main 

channel indicate debris flows in about 1790 and 1830; 

more recent flows scarred trees in 1935, between 1960 

and 1962, and 1985.

SITE 7, ABOVE JUNIPER FLATS

Site 7 (fig. 3) is the most downstream study site. 

Except for occasional rather coarse lobes, the surface is 

very fine grained. Debris flows appear to have moved 

from east to west across the fan. Junipers of various 

ages are locally partly buried by fine-grained deposits. 

The 1935 event apparently deposited fine sediments 

over large areas of the site. Subsequent debris flows 

have both deposited sediments upon the 1935 surface 

and, in other places, eroded it. Cores and cross sections 

from junipers indicate a debris flow in about 1840, 

which contributed substantially to the fan at site 7. 

Geomorphic evidence suggests that the 1935 event approximated the 1840 flow in magnitude. Smaller debris 

flows in about 1952, about 1960, 1974, 1977, and 1985 

reached site 7.

BOLAM CREEK

SITE 8, UPPER BOLAM

Site 8 (fig. 3) is located in a fairly deep valley with 

side slopes overlain by pyroclastic material. The valley 

bottom is characterized by levees and lobes left by a 

debris flow in 1974. These levees and lobes are largely 

devoid of trees except for small stunted seedlings whose 

average age is about 8 years old. Another more recent

flow may have occurred within the levees of the 1973- 

74 event (Miller, 1980) but there is no known dendrochronologic evidence. These recent debris flows 

overlie older deposits dated to 1730, 1800, 1924, 1935, 

and 1955. Scars and eccentric growth patterns support 

all debris-flow dates at site 8 except for the two oldest 

(1730 and 1800), which are based on cohort age.

SITE 9, BELOW FORD

From site 9 (fig. 3) up to the lower reach of site 8, the 

valley bottom is broad with many debris- and 

pyroclastic-flow surfaces. The area immediately adjacent to the present channel is dominated by debris-flow 

deposits. The 1935 debris flow left substantial levees 

along the channel that may have been reworked by 

more recent flows in 1955 and 1974. Nearby debris-flow 

terraces have minimum formation dates of 1670,1730, 

and 1845 from cohort ages. The channel from site 9 to 

the confluence with Whitney Creek is part of the 

Whitney-Bolam alluvial fan with a characteristic shallow channel bed relative to topbanks. Locally the banks 

may be cut and reveal a debris-flow stratigraphy similar to those described on Whitney Creek (Osterkamp 

and others, 1986).

SITE 10, ABOVE CONFLUENCE WITH WHITNEY CREEK

Site 10 (fig. 3) is similar to site 9 although the channel is wider and debris-flow terracing more common. 

Terrace surfaces provided minimum ages of 1730, 

1785, 1800, 1845, and 1897. The 1935 event left substantial levees that have been reworked by numerous 

smaller debris flows that could not be dated. A recent 

event left a mud plaster still evident about 1.5 m above 

the present channel. This site and those upstream to 

a lesser degree suggest many small debris flows have 

occurred since 1935 at a greater frequency than on 

Whitney Creek. It is probable that either these recent 

events occurred with such frequency that tree establishment is prevented or altered; the last flow removed 

evidence of events and occurred so recently that 

seedlings have not yet become established. However, 

none of these recent events have overtopped the 1935 

levees. Apparently these small, recent events stop flowing wholly within the channel above the confluence 

with Whitney Creek, as evidenced by steplike lobes 

within the channel. Some events may have proceeded 

into Whitney Creek but have been reworked by fluvial 

action in the main stem where greater discharges of 

water occur.

SITE 11, BOLAM FAN NORTH OF CHANNEL

Site 11 (fig. 3) is a broad fan with generally finegrained deposits. Dendrogeomorphic evidence suggests
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B37

that at least some debris flows left the Bolam Creek 

channel and flowed north over the fan. Debris flows in 

this area appear to rapidly lose their coarse fragments, 

and thus leave sheets of increasingly fine-grained material downslope. Tree-ring dates from scattered buried 

trunks document recent debris-flow activity at site 11 

in 1896, 1935, 1955, and 1973-1974. Shallow channel 

areas along the right bank just below site 9 indicate 

that debris flows may have left the channel in this 

reach. Unfortunately fires and lumbering have removed all but a few scattered trees, which is typical 

along the Whitney-Bolam fan.

MUD CREEK

SITE 12, IN DEEP INCISEMENT

Site 12 (fig. 3) is located in a steep, relatively narrow 

valley formed by the major Mud Creek incisement. The 

valley walls bear evidence of massive slope failures 

some going the whole height of the gorge (250 m). The 

valley floor is characterized by a locally present low 

terrace. Trees on this terrace predate the debris flows of 

1924-31, although boulder levees on the channel ward 

edge were left by flows in 1924 and in 1931. Thus, these 

recent large events were relatively small here and 

bulked through this reach and below. Trees on the terrace show evidence for events in about 1881 and 1910. 

Aggraded mounds on valley-floor areas across from 

valley-wall failures are possible evidence that landslides ran up the opposite bank and may have temporarily dammed Mud Creek. One of these mounds supports trees with minimum ages that suggest 

landsliding occurred in the early 1880's. Osterkamp 

and others (1986) discuss the significance of valleywall failure in relation to debris-flow activity.

SITE 13, 3 KILOMETERS ABOVE DAM

Site 13 (fig. 3), although still in the major incisement, has a relatively broad valley bottom. The stream 

is entrenched deeply on the right bank and exposes a 

complex of terraces to a height of 20 m above the bed 

(fig. 11). The degradation of the channel probably occurred during the historic 1924-31 events; the lowest 

terrace is older than the historic events. Thus, the flows 

of 1924-31 were probably still bulking through this 

reach. Site 13 is geomorphically similar to the Whitney 

Creek gorge reach. The complex of terraces is heavily 

forested and allowed for fairly accurate dating of four 

debris flows. The terrace complex contains debris-flow 

surfaces dated to 1630, 1740, 1881, and 1910 (fig. 11). 

Levees have been deposited on parts of the terrace complex in 1840, 1924, 1931, and 1955. Immediately upstream of these high terraces the stream crowds the left

bank. Low levees on the right-upstream bank support 

trees that document the historic flows of 1924-31 and 

about 1955, the latter being the lowest levee.

SITE 14, 1 KILOMETER ABOVE DAM

From site 14 (fig. 3) to downstream the events of 

1924-31 become increasingly depositional. Lobate 

surges of the 1924 and 1931 debris flows came to rest on 

midlevel terraces presently 15 m to 20 m above the 

channel. Site 14 is characterized by three distinct terrace levels on the left bank; the highest debris flow was 

deposited about 1840. The age of the midlevel terrace is 

probably about 1910, although deposits from 1924 and 

1931 now cover the surface and have left pronounced 

levees at the channelward edge. Tree ages on the lowest terrace suggest the surface formed in about 1964. 

No trees below the highest terrace are older than the 

1924-31 events. The lobate surge deposits probably occurred on the recessional limb of the debris-flow event.

SITE 15, DAM SITE

The dam at site 15 (fig. 3) was built in response to the 

destructive 1924 debris flow. Fluviation and subsequent flows, particularly in 1931, have filled the channel upstream of the dam, whereas the channel below 

the dam has been incised into terraces. The historic 

events of 1924-31 dominate much of the fan developed 

at and below site 15. Apparently these historic events 

occurred as anastomosing flows over the fan and killed 

many trees by root and stem burial (Beardsley and 

Cannon, 1930). However, higher portions of the fan 

where trees were not killed support older trees from 

which evidence was recovered for debris-flow activity 

in about 1800 and 1881. A small in-channel terrace 

supports vegetation which documents a small debris 

flow in 1964.

SITE 16, PIPELINE CROSSING

Site 16 (fig. 3) as well as the two sites downstream, 

reflects the highly aggradational nature of debris-flow 

activity on the lower reaches of Mud Creek. The channel is incised 2 m to 4 m into terrace deposits and the 

texture of deposits become increasingly fine grained. 

The fan supports a relatively sparse tree cover that 

documents five debris flows about 1800, 1910, the historic 1924 and 1931 events, and a small flow in 1964. 

Dendrochronologic evidence of the 1881 event was not 

found.

SITES 17 AND 18, BETWEEN ROAD 13 CROSSING (DEBRIS 

FLOW NATURAL AREA) AND CA 84 CROSSING

Sites 17 and 18 (fig. 3) are similar to Site 31 except 

for increasingly sparse tree cover and finer textured
B38 DEBRIS-FLOW ACTIVITY AND ASSOCIATED HAZARDS, MT. SHASTA, CALIF.

deposits. The tree cover increases with distance from 

the channel which presumably reflects a gradual thinning of the 1924-31 deposits. Old trees typically 50 m 

to 75 m from the channel document the 1881 debris 

flow through minimum ages and anomalies in treering sequences. For detailed descriptions of these and 

adjacent areas see Dickson and Crocker (1952; 1953), 

Hill and Egenhoff (1976), and Sollins and others (1983).

ASH CREEK

SITE 19, UPPER ASH CREEK CROSSING

Site 19 (fig. 3) is dominated by deposits left by recent 

debris flows in 1939,1962, and 1977. These deposits are 

the highest in elevation occurring at the head of the 

upper fan. Above site 19 the stream is deeply incised to 

near its head at Wintun Glacier, as is typical of all 

major streams in their upper alpine reaches. The left 

bank above the recent deposits is composed of pyroclastics, whereas the right banks and areas south of the 

channel are debris-flow deposits. Debris flows appear 

to preferentially deposit on or overtop the right bank at 

the upper part of this site. The 1939 event left the 

channel at site 19 and scarred trees on the fan surface 

for hundreds of meters downslope and adjacent to the 

channel; most deposition from this event occurred farther downstream of site 19. A plan view of site 19 is 

shown in figure 14. The debris flows of 1962 and 1977 

were depositional throughout the site leaving distinct 

levees in the upper part and spreading into a broad 

sheetlike lobe (fig. 14). The 1962 event was substantially larger than the 1977 event and deposited lobate 

sheets farther downslope and over a broader area 

(fig. 14). The channel is perched on the surface of the 

1977 deposit (fig. 15) before it shifts to the right side of 

the 1962 surface downslope. Perched channels are indicative of recent events, where levees confine the 

channel to the higher central part of the deposit 

(fig. 15).

The 1977 debris flow is historically documented 

(Miller, 1980). Tree damage from the 1977 event, as 

well as from events in 1962 and 1939, is widespread. At 

the extreme left edge of site 19 large trees bear evidence of a debris flow about 1800. The 1977 debris flow 

was a small flow lying wholly on the 1962 surface and 

occupying about Vio the area of the 1962 surface. Substantial overbank deposition from the 1939 debris flow 

downstream of site 19 suggests that it was larger than 

the 1962 event. However, most material in the 1939 

debris flow was transported through site 19 (some bulking may have occurred here), whereas the site is dominated by the larger sheetlike deposit of the 1962 flow. 

A small debris flow also occurred in 1958, but evidence 

was found only at the highest part of site 19. Scarred

trees adjacent to the path of the 1939 event indicate 

passage of coarse material in 1931 and 1952 as well, 

although no geomorphic evidence could be found for 

these two events.

SITE 20

Site 20 (fig. 3) is located at and immediately below 

the lower part of the area devastated by the 1962 debris 

flow. The stream is incised into deposits from the 1962 

flow only up to about 1.5 m. The incisement abruptly 

becomes deeper off the 1962 surface. At site 20 the 

terracing (fig. 16) begins and continues to the gorge. 

Stepped channel fill also begins along this reach. Deposits lateral to the channel are substantially more fine 

grained than those upstream. The 1977,1962, and 1958 

events were confined to the channel at site 20 and 

downstream, occurring as small relatively coarsegrained terraces within the major channel incisement. 

The 1939 event deposited an intermittent sheet of finegrained material on the topbank near the channel. 

Roots growing before 1939 show the thickness of the 

1939 deposit (fig. 17). Evidence from tree rings was 

determined for events in 1898, 1873, and about 1800. 

The 1898 event left a continuous sheet of fine-grained 

material at the topbank and immediately below the 

1939 deposit. The 1873 debris flow is documented only 

at this site and site 22 and was undoubtedly a small 

event. Other evidence of the 1873 debris flow was obliterated upstream by subsequent flows, particularly the 

1962 debris flow. Large trees on the right bank are a 

cohort that became established about 1800 (fig. 15).

SITE 21, MILITARY PASS FORD

The fan at site 21 (fig. 3) is broad and extends largely 

to the right or south of the present channel. Debris-flow 

deposits more recent than 1725 become increasingly 

more apparent from south to north toward the channel, 

which suggests that the channel has shifted northward 

since 1725. Deposits left by the mid-1700 event are the 

oldest and largest debris flows on Ash Creek for which 

there is tree-ring evidence (fig. 16). The fan above the 

gorge is dominated by these deposits except at the uppermost two sites. Laterally the 1725 and mid-1700 

deposits extend from near the present channel south to 

the Cold Creek channel and may have contributed to 

the formation of the Cold Creek drainage (Osterkamp 

and others, 1986). The mid-1700 event is termed the 

Cold Creek episode (Osterkamp and others, 1986). 

The period between 1725 and 1768 had numerous flows 

on Ash Creek. The largest of these events occurred 

about 1725,1728, and around 1740; subsequent events 

until 1768 were smaller and probably related to continued upstream channel instability initiated by the massive flows occurring during the early part of the Cold
DENDROGEOMORPHIC EVIDENCE AND DATING, DEBRIS FLOWS, MT. SHASTA, CALIF. B39

Creek episode. The present channel configuration of 

both Cold Creek and Ash Creek above the gorge is 

largely a result of the Cold Creek episode (Osterkamp 

and others, 1986). The more recent events documented upstream in about 1800,1898,1939,1962, and 

1977 are represented by terraced deposits near the 

present channel (fig. 16). The 1977 deposit is only a 

small in-channel, barlike feature and may be a lag 

deposit of a sediment-rich flood associated with the upstream 1977 debris flow.

SITE 22

Site 22 (fig. 3) is quite similar to site 19 in overall 

appearance and the deposits left by events during the 

Cold Creek episode dominate the fan surface except 

near the channel. Dendrogeomorphic evidence occurs 

for the 1873, 1898, 1939, 1962, and 1977 events as 

described for upstream sites. A portion of the channel 

along this reach is underlain by lava that has apparently caused even small flows to spread locally over the 

fan. Otherwise, the channel becomes increasingly more 

incised in this lower part of the upper fan.

SITE 23, JUST ABOVE JUNCTION SPRING

Site 23 (fig. 3) is not located along the main stem of 

Ash Creek but is an area subject to debris flows which 

overtop the channel incisement. Site 23 is located in a 

valley just above the Ash Creek gorge, which heads at 

upslope debris-flow deposits. The valley, particularly 

upstream, has been subjected to fine-grained deposition. Most large trees have partly buried trunks, which

indicate that at least 30 cm of aggradation has occurred, 

here since the Cold Creek episode. Cohorts of trees and 

suppression sequences document depositional events in 

1728-1740, 1898, 1939, and 1962. The most recent 

event may represent the smallest magnitude necessary 

to affect this area.

SITE 24, ASH CREEK GORGE

The gorge site 24 (fig. 3) has small depositional areas 

compared to sites upstream or downstream. A narrow 

terrace supports trees which have been scarred by 

events in 1898,1939, and 1962. The debris flows of the 

Cold Creek episode were largely transported through 

the gorge and probably destroyed most trees. However, 

the debris-flow strata exposed on the channelward terrace edge may have been laid down during the Cold 

Creek episode. Coarse materials are located to about 

0.5 km below the gorge. Below this secondary fan at the 

gorge mouth, the lower fan spreads into a fine-grained 

apron that extends from lower Ash Creek to the confluence with the McCloud River.

SITE 25, AT OLD MILL SITE

Site 25 (fig. 3) is located on the fine-grained lower fan 

and typical debris-flow features are lacking. Site 25 has 

only a mildly undulating surface indicative of fluvial 

activity. Large trees with partly buried trunks often 

have suppression-release sequences which suggest depositional events in 1725-28,1800,1898, and 1962. As 

is the case on lower elevation sites along Mount Shasta 

streams, it is difficult to infer the relative magnitude of 

a series of depositional events from tree-ring data.

.S. G.P.O. 198?-l8l-40?:60015