Geologic Relationships 

Of Slope Movement in 

Northern Alabama 

u.s. GEOLOGICAL OSURVEY BULLETIN 1649 

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Geologic Relationships 

Of Slope Movement in 

Northern Alabama 

By JOHN S. POMEROY and ROGER E. THOMAS 

U.S. GEOlOGICAl SURVEY BUllETIN 1649 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1985 

For sale by the Distribution Branch, U.S. Geological Survey, 

604 South Pickett Street, Alexandria, VA 22304 

Library of Congress Cataloging-in-Publication Data 

Pomeroy, johnS., 1929-

Geologic relationships of slope movement in northern Alabama. 

(U.S. Geological Survey bulletin ; 1649 

Bibliography: p. 13 

Supt.ofDocs.no.: I 19.3:1649 

1. Earth movements-Alabama. 2. Slopes (Physical geography)-Aiabama. I. Thomas, Roger, E. II. Title. Ill. 

Series. 

QE75. 89 [QE598] 557.3 s [551.4'36] 

84-600402 
CONTENTS 

Abstract 1 

Introduction 1 

Cumberland Plateau 3 

Sand Mountain 3 

Jackson County Mountains 4 

Warrior Basin 7 

Highland Rim 10 

East Gulf Coastal Plain 10 

Summary 11 

References 13 

FIGURES 

1. Map showing area investigated for slope-stability study and physiographic 

regions in northern Alabama 2 

2. Photographs showing recent and older slope movements in northern 

Alabama 6-7 

3. Maps showing recent and older slope movements and slide-prone terrain, 

northern Alabama 8-9 

4. Map showing slope movement-prone areas in northern Alabama 12 

TABLE 

1. Stratigraphic units whose derivative soils are moderately to highly susceptible 

to movement 4-5 

Contents Ill 

Geologic Relationships of Slope Movement in 

Northern Alabama 

By John S. Pomeroy and Roger E. Thomas 

Abstract 

Slope-stability problems in northern Alabama result 

from slope movement that takes place within all major 

physiographic sections which include the Cumberland 

Plateau, Highland Rim, and Eastern Gulf Coastal Plain. 

Slope movements, commonly debris slides, slumps, earthflows, and complex forms, take place in the colluvium or 

at the contact between the colluvium and the underlying 

weathered mudstone or shale in the Cumberland Plateau. 

Slopes underlain by the Pennington Formation and for the 

upper part of the Bangor Limestone of Late Mississippian 

age are the most susceptible to movement. Toppling failures, involving the overlying subhorizontal sandstone 

caprock of the Pottsville Formation of Pennsylvanian age, 

are largely controlled by separation along the vertical 

joint faces and by undermining caused by rapid weathering of the underlying incompetent mudstones and shales 

of Mississippian age. Old slope movements as long as 0.9 

km have been documented near Huntsville. Road construction in that area reactivated a small part of one old 

slope movement. In the extreme western part of the Cum--

berland Plateau, colluvium derived from shale and mud--

stone of the Parkwood Formation of Late Mississippian 

and Early Pennsylvanian age is prone to sliding. 

Slopes underlain by the Pride Mountain Formation 

of Late Mississippian age in the Highland Rim section 

show evidence of present and past instability. Recent slid--

ing has taken place in colluvium derived from mostly gray--

ish-green shale. Two large prehistoric bedrock slumps (0 . .5 

and 1.3 km wide) have displaced the overlying Hartselle 

Sandstone in a northwest-trending, joint-controlled valley 

southwest of Tuscumbia. 

Sand, gravel, and less abundant clay of the Tusca--

loosa Group of Late Cretaceous age mantle the Eastern 

Gulf Coastal Plain in northern Alabama. Highway con--

struction in this unit, near Hamilton, has caused major 

slope movements whose failure surfaces can be traced to 

thin clay seams. 

INTRODUCTION 

A large part of northern Alabama was examined 

1n 1979-1981 for slope stability (Pomeroy, 1982b; 

Thomas, 1979, 1982) as part of a comprehensive investigation involving the Appalachian Plateau Province. Adjoining areas of the Interior Low Plateaus 

and Coastal Plain Provinces to the north and west 

were also examined. This area is bordered by Sand 

Mountain in the east and by longitude 88 ° in the 

west. The State boundary and latitude 34 ° border the 

area in the north and south, respectively (fig. 1). 

Aerial photography at scales of 1:20,000 (1971, 

1972), 1:40,000 (1977-1979), and 1:80,000 (1977) 

was used in the study. Photo interpretation was followed by reconnaissance from vehicles and selected 

foot traverses. Included in the inventory were identification of recently active and historic landslides, prehistoric landslides, and the outlining of zones considered by the investigator to be most susceptible to 

slope failure on the basis of landslide incidence, rock 

and soil textures, and topography. Pomeroy was responsible for the inventory west of longitude 86 o. 

Thomas investigated the Appalachian Plateau Province east of longitude 86 ° (fig. 1 ). 

In this report, we have adopted the term slope 

movement rather than landslide as a general, inclusive term except for movements that involve only 

sliding. Landslide has been widely used as an allinclusive term for almost all types of slope movement 

including some that involve little or no sliding 

(Varnes, 1978, p. 11). The popular geomorphic term, 

mass movement, is synonymous with slope movement 

and is not used in this report. 

Five types of slope movement (Varnes, 1978, 

fig. 2.1) are present in northern Alabama. They include falls (rockfalls), topples, slides (earth slumps, 

debris slides), flows (debris and earth flows, debris 

avalanches), and complex movements (slump-earthflows, debris slide-earthflows). 

Rock falls are extremely rapid free falls of bedrock. Alternating competent and incompetent lithologies, in addition to closely spaced vertical joints 

parallel to the major drainages, are contributing factors to the process. Topples are rock blocks that have 

Introduction 
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A Locality discussed in text 

Boundary between physiographic sections 

Boundary between physiographic districts 

Physiographic unit boundaries 

are slightly modified from Sapp and 

Emplaincourt, 1975 

EXPLANATION 

EGCP, East Gulf Coastal Plain 

JCM, Jackson County Mountains 

LIM, Little Mountain 

MOV, Moulton Valley 

SM, Sand Mountain 

SQV, Sequatchie Valley 

TV, Tennessee Valley 

WB, Warrior Basin 

Figure 1. Map showing area investigated for slope-stability study and physiographic regions in northern Alabama. 
rotated forward. Slides are either earth slumps involving rotational movement with an upward curving rupture surface or are debris slides which take 

place along planar or mildly undulatory surfaces and 

are called translational movements. Both types of 

slide movements can be very slow to rapid. Flows in 

northern Alabama are of three types, ranging in 

movement patterns from extremely rapid (debris avalanche) to very rapid (debris flow) to rapid to very 

slow (earth flows). Flows in surficial materials show 

movement resembling that found in the flows of viscous fluids. 

A debris avalanche has a long and relatively 

narrow track along a steep mountain or hill slope and 

is usually preceded by copious precipitation. A debris 

flow, similar to a debris avalanche, is commonly a 

wider and less viscous movement. An earthflow commonly shows shear surfaces along the flanks and basal surface even though the distribution of velocities 

within the displaced material may indicate plastic 

flow (Varnes, 1978, fig. 2.1). Indeed, most slope 

movements are complex in that features of two or 

more basic slope movements are represented, as in 

slump-earthflows, debris slide-earthflows, and so on. 

Complex movements involve an upper zone of depletion (slump, debris slide) and a lower zone of accumulation or deposition (flow). 

Rocks exposed in the area range from Ordovician to Cretaceous in age. The relatively simple structure is made up of subhorizontal strata except for the 

Sequatchie Valley west of Sand Mountain (fig. 1 ). 

The physiographic sections include the Cumberland 

Plateau (Appalachian Plateaus Province), Highland 

Rim (Interior Low Plateaus Province), and the East 

Gulf Coastal Plain (Coastal Plain Province). Slope 

stability is discussed by physiographic region. 

CUMBERLAND PLATEAU 

The Pottsville Formation (table 1 ), which caps 

the Cumberland Plateau, is the most widespread and 

conspicuous stratigraphic unit in northern Alabama. 

The revised stratigraphic nomenclature of the Mississippian units in northern Alabama indicated that the 

Pennington Formation (table 1) is areally restricted 

to the northeast part of the region (Thomas, 1972, p. 

84). The Pennington Formation grades westward into 

the upper part of the Bangor Limestone (table 1), 

which includes light-green and maroon shale and 

mudstone interbeds in its upper part. The Parkwood 

Formation (table 1) in the western part of the Cumberland Plateau lies between the Bangor Limestone 

and the Pottsville Formation. 

The Cumberland Plateau section in divided into several physiographic districts (Sapp and Emplaincourt, 197 5). The districts applicable to this discussion are Sand Mountain, Jackson County 

Mountains, and the Warrior Basin (fig. 1). 

Sand Mountain 

Sand Mountain is a submaturely dissected synclinal plateau of moderate relief capped by the Pottsville Formation. The boundaries are distinct except 

at the southwest end where Sand Mountain subtly 

merges with the Warrior Basin. The sandstone escarpment along both sides of Sand Mountain ranges 

in relief from 122 m ( 400 ft) at the south end to 305 

m ( 1,000 ft) at the (north end). Slope movements are 

common only along the flanks of the plateau. 

That part of the east side of Sand Mountain 

that was inventoried for slope movements is largely 

covered by colluvium within which small (<30 m 

wide) debris slides, slumps, and complex forms are 

found above and below roads. 

The west side of Sand Mountain has greater 

relief than the east side. The slope is largely covered 

by colluvium and is generally slide-prone. All recent 

slope movements have been induced by man and are 

largely slump-earthflows or debris slide-earthflows. 

For example, along Alabama 73 less than 1 km 

southwest of the tri-State intersection (AL-TN-GA), 

colluvial movements are restricted to the upper part 

of the slope underlain by the Pennington Formation 

(fig. 1, locality A). A more extensive area within 

which the movements are larger is on the upper side 

of Alabama Route 11 7, 25 km northeast of Scottsboro (fig. 1, locality B). Parent materials are the 

upper part of the Bangor Limestone and the Pennington Formation. Slope movements in the spoil 

banks of strip mines are 8 km south of locality B (fig. 

1 ). 

Most slope movements noted at Bucks Pocket 

Tri-County Park (fig. 1) originated during or after 

road construction and took place in colluvium masking Bangor Limestone. One such movement, a 38-mwide slump-earthflow, was triggered midway up the 

south-facing slope above South Sauty Creek adjacent 

to the upper side of the road. Thin soil ( < 1 m thick) 

masks reddish-purple mudstone. Several slumps, as 

wide as 45 m, are present above an improved road at 

nearby Morgan Cove (fig. 1) and incorporate red soil 

and weathered red mudstone of the Bangor 

Limestone. 

A well-defined prehistoric (?) example of a rocktoppling failure (fig. 2A) is found along the same 

slope and involves an area of about 20,000 m2

• The 

Cumberland Plateau 3 
Table 1. Stratigraphic units whose derivative soils are moderately to highly susceptible to movement 

[Asterisk(*) indicates the most susceptible units] • 

Geologic unit Lithology Physiographic section 

Tuscaloosa Group* ----------------- Sand, gravel, clay ------------------ Eastern Gulf Coastal Plain. 

Pottsville Formation -- --- - --- - - --- - Sandstone, shale, Cumberland Plateau. 

claystone, conglomerate. 

Parkwood Formation - - --- - - - - - - - -- - Shale, mudstone, clay- Cumberland Plateau. 

stone, sandstone. 

Pennington Formation* ------------- Shale, mudstone, clay- Cumberland Plateau. 

stone, limestone, sand 

stone. 

Bangor Limestone· -- - -- -- -- - - -- - - - - Limestone, mudstone, Cumberland Plateau. 

claystone. 

Pride Mountain Shale, mudstone, clay- Highland Rim. 

Formation·. stone, limestone, 

sandstone. 

subhorizontal sandstone caprock of the Pottsville 

Formation is largely shattered and broken by separation along vertical joint faces. The toppled blocks dip 

15-20° downslope, at distances of about 8 m from 

the caprock, and are increasingly rotated and disoriented at larger distances from the point of separation. 

Sandstone-boulder scree is more prevalent at the base 

of the slope. The bedrock beneath these failures includes both the Bangor Limestone and the Pennington Formation. 

The toppling movement is believed to have 

been caused by initial horizontal slip along bedding 

in the weathered mudstone (or claystone) in the upper part of the Pennington Formation followed by 

outward rotation of the blocks. The slope movement 

is classified, at least in part therefore, as a secondary 

toppling failure (Evans, 1981 ). 

Above the newly constructed Alabama 22 7, east 

of Gunterville Lake, are several sizable slope movements (figs. 1, locality C; 3A). The highway cuts 

across the lower part of an extensive colluvial slope 

and is oriented roughly parallel to the major subvertical joint direction (N. 75o W.). In a steeply dipping 

roadcut (83°) at locality A (fig. 3A), light-green and 

red mudstone beds of the Pennington Formation(?) 

or upper Bangor Limestone(?) overlie a cliff-forming 

limestone at the lower edge of the cut. At locality B 

the surface of the landslide area has been modified by 

man, but several large, fresh, discontinuous scarps 

along a 21 o (39 percent) slope indicate very recent 

movement. Movements have taken place in both the 

colluvium that overlies mudstone and at the colluvium-weathered mudstone interface. The prominent 

joint trend is the same as at locality A. Springs were 

noted at the contact of the base of the cliff-forming 

sandstone. Upslope from the new road cut, a 6-m4 Geologic Relationships of Slope Movement in Northern Alabama 

high exposure of boulder colluvium consists of older 

toppled blocks of sandstone that were undermined by 

rapid weathering of the less competent mudstones of 

the Pennington Formation. Two previous sinuous 

highway routes (fig. 3A) avoided major cut-and-fill 

operations, and only minimal slope-movement 

problems occurred. 

A road cut with a slope greater than 20° above 

Alabama 227, 12 km southwest of locality C (fig. 1) 

may have been a factor in the genesis of a 45-m-wide 

slump in forested colluvium above the road (fig. 1, 

locality D). The slope is 9 o ( 16 percent) at the head of 

the slump and increases downslope to 17° (32 percent). The head, which is 50 m upslope from the 

road, is within the upper 35-40 m of the Bangor 

Limestone, which locally consists of interbedded 

limestone and mudstone. Slope movements 2 km 

southwest along the same road and above U.S. 431 

south of Guntersville (fig. 1, locality E) took place in 

colluvium derived from rocks at about the same 

stratigraphic horizon. 

Jackson County Mountains 

The Jackson County 1dountains (fig. 1) is a submaturely dissected plateau which has relief ranging 

from 274m (900ft) to 335m (1,100 ft). The region is 

characterized by mesas capped by Pottsville Formation within which valleys are cut into limestone of 

Mississippian age. 

Whereas most of the slopes along the east and 

west sides of Sand Mountain are largely colluvial and 

can be classified as generally unstable, slopes in the 

Jackson County Mountains, even though of greater 

relief on the average, are only partially unstable. 
WEST 

~TU~CALOOSA GROUP* 

-~-~ ~Uppe' c,etaceous) 

POTTSVILLE FORMATION 

(Lower and Middle Pennsylvanian) 

PARKWOOD 

FORMATION 

Lower Pennsylvanian/ 

Upper Mississippian,-

EAST 

PENNINGTON FORMATION* 

(Upper Mississippian) 

BANGOR LIMESTONE* 

(Upper Mississippian) 

FLOYD SHALE -

(Upper Mississippian) 

(not in area) ,------------'"""'-

I 

HARTSELLE SANDSTONE 

(Upper Mississippian) 

PRIDE MOUNTAIN 

FORMATION* -

(Upper M ississippianl_ 

TUSCUMBIA LIMESTONE 

(Upper Mississippian) 

FORT PAYNE CHERT 

(Lower Mississippian) 

---

(Modified from Thomas, 1972) 

Generally, the only slope movement-prone rock zone 

is about 60 m thick and stratigraphically occupies the 

upper Bangor Limestone interval and the position of 

the Pennington Formation, which forms the upper 

part of most slopes in the area. More resistant limestone of Mississippian age commonly crops out along 

the lower and middle parts of the slopes. In the eastern part of the region, where several small slope 

movements were identified, a colluvial mantle commonly was found to extend to the base of a slope. In 

contrast, in the western part of the Jackson County 

Mountains in the Huntsville area, the lower and middle slopes are almost always ribbed by bedrock (fig. 

2C). Thus, extensive debris avalanches apparently do 

not exist in the western part because a supply of 

colluvium is absent a short distance downslope from 

the head area. For example, one debris avalanche 8.0 

km north of Paint Rock (fig. 1) terminated as soon as 

the colluvial movement encountered limestone 

ledges. 

All but two observed recently active slope 

movements in the areas southwest, west, northwest, 

and north of Scottsboro (fig. 1) and in the Huntsville 

area took place in the regolith overlying upper Bangor Limestone and Pennington Formation. Nearly 

one half of all roads traversing colluvium that overlie 

these formations have been affected by slippage 

and/or flowage. The slope movements are largely 

slump-earthflows showing an upper zone of depletion 

and a lower zone of accumulation (Varnes, 197 8). 

A large 0.2- km-long recently active colluvial 

slope movement (fig. 3B), best defined as a slumpearthflow, took place along an east-facing forested 

slope 8 km north of Paint Rock (fig. 1). The head, 

about 90 m wide with an irregular outline and subsidiary scarps, lies on a 13 o (24 percent) slope. Above 

the head scarp is a 30-m-wide, nearly flat bench where 

water ponds from springs located along the Pennington and Pottsville contact further upslope. Levees on both sides are well developed downslope. The 

toe stands 2.0-2.5 min relief along a 14° (27 percent) 

slope. Adjacent to the foot of the slump-earthflow are 

limestone outcrops. Below the foot, a considerably 

steeper slope with abundant ledges and scant colluvium extends to the base of the slope. 

An old slope movement, perhaps a debris flow, 

was identified nearly 1 km west of the recently active 

slump-earthflow (fig. 3B). The 0.5-km-long movement has hummocky topography and is capped with 

boulders of Pottsville Formation. Limestone ledges 

are adjacent to the prominent gulch east of the movement (fig. 2D). In the foot area, the surface of the old 

flow is 7.5-9.0 m above the drainage. 

Other old slope movements, including probable 

debris flows, were identified along both sides of 

Green Mountain southeast of Huntsville (fig. 3C) and 

in the Guntersville Lake area (fig. 3D). In each case, 

the slope movement appeared to originate at or below the Bangor Limestone and Pottsville contact resulting in tilted (slumped) benches in the colluvium 

overlying the Bangor Limestone and possibly in detached blocks of rock. 

Cumberland Plateau 5 
A 8 

D 

c 

E F 

6 Geologic Relationships of Slope Movement in Northern Alabama 
G H 

Figure 2. Photographs showing recent and older slope movements, northern Alabama. Mb, Bangor Limestone; Mp, 

Pennington Formation; Pp, Pottsville Formation. 

A Prehistoric(?) toppled blocks from Pottsville Formation as seen from caprock at Point Rock. Bucks Pocket Tri-County 

Park 28 km northeast of Guntersville; Grove Oak 7 1/2-minute quadrangle. 

B. Prehistoric(?) toppled blocks of Pottsville Formation downslope from outcrop at far left of figure 2A. Unstable 

colluvium and weathered rock of Pennington Formation in foreground was recently active (see locality Bon fig. 3A). 

Alabama 227, 18 km northeast of Guntersville. Columbia City 7 1/2-minute quadrangle. 

C. Interval (60 m thick) susceptible to slope movement in upper part of Bangor Limestone (Mb) denoted by dashed 

lines. Note excellent outcrops of Mb and older limestone units beneath weak zone. West edge of Cumberland Escarpment 12 km south-southeast of Huntsville. Huntsville 7 1/2-minute quadrangle. 

D. View laterally across east side of probable debris flow (Pp colluvium) to Bangor Limestone (Mb) ledges (see fig. 38). 

Cumberland Plateau 24 km east of Huntsville. Paint Rock 7 1/2-minute quadrangle. 

E. View up lateral margin (dashed line) of prehistoric probable debris flow (see fig. 3£). Cumberland Plateau escarpment 

16 km southeast of Russellville. Newburg 71/2-minute quadrangle. 

F. Head of translational (planar) slide in woodland above road. Weathered mudstone from Bangor Limestone underlies 

head. Cumberland Plateau escarpment 38 km south-southwest of Huntsville. Center Grove 71/2-minute quadrangle. 

G. Colluvial slope failure above U.S. 43. Grayish-green weathered shale and soil of Pride Mountain Formation. Little 

Mountain section 13 km northeast of Russellville. Russellville 71/2-minute quadrangle. 

H. Head of slope failure in Tuscaloosa Group along U.S. 43, 8 km south of Hamilton. Eastern Gulf Coastal Plain section. 

Hamilton SW 7 1/2-minute quadrangle. 

Recent slope movement took place along the 

lower slope at Weatherly Cove adjacent to the southeast part of Huntsville (fig. 1 ). This 40-m-long, 40-mwide colluvial movement is part of a larger (0. 9 km 

by 0.5 km) old movement. Road construction along 

the base of the slope was a factor triggering the 

movement. 

Warrior Basin 

The Warrior Basin (fig. 1) is a synclinal, submaturely to maturely dissected plateau developed upon 

the Pottsville Formation. The north-facing sandstone-capped escarpment at the northern edge of the 

basin has relief ranging from 61 m (200 ft) in the 

western part to 183 m (600ft) in the eastern part. In 

the inventoried area, the Basin slopes gently southward and has relatively shallow incised drainages. 

Slope movements occur frequently in colluvium overlying the upper part of the Bangor Limestone 

from Cullman northeastward to the Tennessee River 

(fig. 1). As the northern rim of the Warrior Basin is of 

relatively low relief northwest of Cullman, the incidence of slope movement is less common there (figs. 

2£ and 3£). Although the upland surface shows moderate incisement in the Pottsville Formation west and 

southwest of Cullman, the slopes are generally stable. 

However, some instability was documented along the 

slopes underlain by the Pottsville Formation bordering Interstate 65, 16 km south of Cullman (fig. 1). 

Spoil-bank failures from strip-mining operations are 

numerous 3 km east of the Interstate. 

The incidence of recently active slope movements in the northeastern part of the Warrior Basin 

is greater than that in the Jackson County Mountains 

because of higher population density with more roads 

Cumberland Plateau 7 
A. Recent man-induced slope movement 18 km northeast of 

Guntersville (see fig. 28). Cumberland Plateau. Columbia 

City 7112-minute quadrangle. 

C. Prehistoric slope movement 15 km southeast of Huntsville. 

Flow stands 2.0-2.5 m in relief near base. Cumberland Plateau. 

Farley 7112-minute quadrangle . 

E. Prehistoric and recently active slope movements 16 km 

southeast of Russellville (see fig. 2£). Cumberland Plateau. 

Newburg 7112-minute quadrangle. 

B. Prehistoric and recent slope movement 24 km east of 

Huntsville (see fig. 2D). Cumberland Plateau. Paint Rock 

7 1/2-minute quadrangle . 

D. Prehistoric slope movement above Guntersville Lake I km 

soutneast of Dam. Cumberland Plateau. Guntersville Dam 

7 1/2-minute quadrangle . 

F. Slope movement-prone terrain 15 km south of Tuscumbia. 

Highland Rim . Russellville 7112-minute quadrangle. 

Figure 3. Maps showing recent and older slope movements and slope movement-prone (s-p) terrain, northern Alabama. Mb, Bangor 

Limestone; Mp, Pennington Formation; Pp , Pottsville Formation; Mpm., Pride Mountain Formation; Mh, Hartselle Sandstone 

8 Geologic Relationships of Slope Movement in Northern Alabama 
G. Prehistoric bedrock slump blocks 15 km southeast of 

Tuscumbia. Highland Rim. Pride 71/c-minute quadrangle. 

Horizontal beds, EB. Strike and dip of beds, ...L.l.O. 

H. Slope movement-prone terrain 7 km south of Hamilton. 

East Gulf Coastal Plain. Hamilton SW 7112-minute quadrangle. 

EXPLANATION 

Recent slope 

movements j ,--·..,. I Older slope 

~--__, 1 movements ~ 

1 "-n 1 Slope movementprone terrain 

0 1 MILE 

0 1 KILOMETER 

CONTOUR INTERVAL 20 FEET 

traversing the slopes of low relief. Most slope movements take place above roads. Several zones of red 

and green mudstone interbedded with limestone are 

observed in highway cuts along the northern rim. 

Commonly, the green mudstone is more clay-rich 

than the reddish to reddish-purple siltier mudstone 

and shale. 

Most of the slope movements are 9-15 m wide. 

One of the larger debris slides (figs. 1, locality F; 2F), 

is more than 30 m wide, has well-defined lateral borders, and is at least 1 0 years old based on vegetation. 

The debris slide originated along a 22 ° ( 41 percent) 

wet slope a few meters below the contact of Bangor 

Limestone and Pottsville Formation and shows 

translational (planar) movement. 

An extensive zone of movements is found along 

Alabama 243, 10 km southeast of Russellville (fig. 1, 

locality G). Highway fill has slumped, but colluvium 

derived from the Parkwood Formation (table 1) also 

is unstable adjacent to the highway fill. At the base of 

the slope, slumped limestone ledges are underlain by 

weathered red mudstone of the Bangor Limestone. 

Stress relief along joints in the limestone parallel to 

the road has dislodged the thick-bedded limestone 

and has surcharged the already unstable slope extending to the highway. According to the nearest 

landowner, the 1970 highway construction caused 

the movements which have now been largely stabilized. The original slope prior to highway construction was about 1 7 ° (30 percent) but is now 35 o (70 

percent). 

Not all slope movements take place in colluvium derived from Mississippian rocks. Small slope 

movements have been mapped within the lower 10m 

of the Pottsville Formation. For example, water penetration down the joint plane in sandstone to an impermeable blue-gray clay caused the slippage of an 

area 60-75 m wide above Alabama 187, 24 km 

southwest of Russellville near the western extremity 

of the Warrior Basin (fig.1, locality H). 

Samples from the upper part of the Bangor 

Limestone and the Pennington Formation in the 

Cumberland Plateau were studied to determine their 

clay mineralogy. Illite is the principal clay mineral 

identified in all samples. The (003)/(001) ratio is less 

than one indicating that the illite is deficient in potassium (Gloria Hunsburger, written commun., 1981). 

Fisher and others ( 1968, p. 79) in Ohio concluded 

Cumberland Plateau 9 
that "simultaneous deposition of ferric iron with degraded illitic clay prevented reabsorption of the 

bonding potassium ion in the depositional environment. The continued presence of iron has greatly inhibited the reconstitution of the clay throughout 

diagenesis and later geologic time." They indicated 

that degraded illites are similar to montmorillonite in 

the presence of water except that expandability is not 

as great. Unstable potassium-deficient illitic soils derived from mudstones and shales are characteristic 

over much of western Pennsylvania (Pomeroy, 

1982a) and southeastern Ohio (Fisher and others, 

1968). 

HIGHLAND RIM 

The Little Mountain district (fig. 1) ofthe Highland Rim section is a submaturely dissected southward-dipping sandstone ridge with as much as 134 m 

( 440 ft) of relief. The Hartselle Sandstone caps the 

less competent Pride Mountain Formation both of 

which are of Late Mississippian age. 

All observed slope movements in the Highland 

Rim have taken place in areas underlain by the Pride 

Mountain Formation (table 1 ). The Pride Mountain 

Formation consists of thick shale units including 

mudstone interbedded with thin beds of limestone 

and sandstone. Recent sliding and flowage have taken place in highly plastic when wetted soil derived 

from mostly grayish-green shale. Major localities include slopes along U.S. 43 between Russellville and 

Tuscumbia (figs. 2G, 3F) and Alabama 24 7 west and 

southwest of Tuscumbia. 

Movements 100-120 m wide were documented 

along slopes as gentle as 9° (16 percent) next to recently widened roads. Cut slopes at grades as much as 

100 percent show movement wherever colluvial 

pockets are found above the road. Filling operations 

frequently appear to have overloaded already inherently unstable slopes (fig. 3F). Although slopes in the 

Little Mountain area south, southwest, and west of 

Tuscumbia have been largely undeveloped, some 

homes have been endangered by slides (C. D. Bowen, 

U.S. Soil Conservation Service, written commun., 

1981 ). 

Two large prehistoric bedrock slumps (0.5 and 

1.3 km wide) have displaced the overlying Hartselle 

Sandstone in a northwest-trending, joint-controlled 

valley, 16 km southwest of Tuscumbia (fig. 3G). Outcrops within the two rotated blocks of Hartselle 

Sandstone dip towards the slope (fig. 3G) in contrast 

to the regional structure. Slumping is probably attributable to penetration of water along northwest-trend10 Geologic Relationships of Slope Movement in Northern Alabama 

ing joint planes in the caprock downward to an impermeable stratum which acted as a failure plane in 

the Pride Mountain Formation. A minimum rotational displacement of 42 m is inferred. At the smaller bedrock block west of the drainage a broad gently 

sloping ( 6-9 o) surface above the outcrops reflects the 

rotational nature of the movement (fig. 3G). 

The decreased incidence of slope movements in 

the Little Mountain area to the east is related to a 

more subtle topography with less relief and facies 

changes from shale to limestone. 

Slopes north of the Tennessee River involving 

colluvium derived from the Chattanooga Shale of 

Late Devonian age and the Fort Payne Chert of Early 

Mississippian age did not show obvious evidence of 

movement. 

EAST GULF COASTAL PLAIN 

The East Gulf Coastal Plain (fig. 1) is a dissected upland with a few broad, flat ridges (Sapp and 

Emplaincourt, 1975) of unconsolidated sediments 

which mask the adjacent physiographic sections to 

the east. 

The Cumberland Plateau and Highland Rim of 

extreme northwestern Alabama are covered by sand, 

gravel, and minor clay of the Tuscaloosa Group of 

Late Cretaceous age (table 1 ). Highway construction 

in this stratigraphic unit in the Hamilton area (fig. 1) 

has caused major slides whose failure surfaces can be 

traced to clay seams. Harris and Causey (1973) have 

divided the Tuscaloosa Group into the Coker and 

Gordo Formations. All of the slope movements seem 

to take place within the older Coker Formation. 

Slope movements have taken place both above 

and below U.S. 43, 78, and 278, 8 km south of Hamilton (figs. 2H, 3H). At the locality south of elevation 

x581 (figs. 2H, 3H) successive earthflow lobes indicate many periods of flowage. The most recent movement is at the northeast edge whereas the oldest and 

most extensive earthflow took place along the southernmost part where 15- to 20-year-old trees are growing on the foot of the flow. A variegated red and lightgray clay, containing little silt, lies beneath some of 

the older lobes and probably acted as a slippage 

surface. 

Most observed slope movements showed evidence of rotation (slumping) and flowage. Slumpearthflows as wide as 60 m were observed along 

slopes cut by secondary roads south and southeast of 

Hamilton. All movements are in the SmithdaleLuverne soils which have a American Association of 

State Highway Officials rating of A-7 and a plasticity 
index of 10-30 (Cotton, 1979) signifying moderate to 

high susceptibility to sliding. 

Large slope movements greater than 60 m in 

width took place during and after construction of a 

new segment of U.S. 43, 3 km northeast of Hamilton 

(fig. 1, locality I). Benching of the slope above the 

east side of the highway has not completely solved 

the problem of active slope movement. A massive 

slope movement on the west side of the highway 

shows perfectly formed 1.5- to 2.5- m-wide "mini" 

slump-earthflows within the larger disturbance. Bluegray clay is commonly exposed in the "floor" of each 

head area and acts as the slippage surface. 

In the Coastal Plain areas southwest, west, and 

northwest of Russellville (fig. 1) reddish and greenish-gray clay is visible in the head areas of all slumpearthflows. 

The incidence of slope movements in the Tuscaloosa Group(?) 1 north of the Tennessee River is 

slight. Nearly vertical highway cuts are found beneath 60-percent-grade slopes without any discernable slope movement. An examination of the exposures in this area failed to reveal any clay within beds 

of highly ferruginous well-cemented gravel. 

SUMMARY 

Stratigraphic units in northern Alabama, whose 

derivative colluvial soils are highly susceptible to 

slope movements, include the Pride Mountain Formation, the Bangor Limestone and the Pennington 

Formation all of Late Mississippian age and the Tuscaloosa Group of Late Cretaceous age. Derivative 

soils formed from the Parkwood (Upper Mississippian and Lower Pennsylvanian) and Pottsville Formations (Lower and Middle Pennsylvanian) are moderately to highly susceptible to slope movements. Slope 

movement-prone areas are shown on figure 4. 

Illite deficient in potassium is the major clay 

mineral found in slope movement-prone soils derived from the upper part of the Bangor Limestone 

1

M. Szabo (Alabama Geological Survey) believes that these sediments are not the Tuscaloosa Group but a younger sequence. 

and the Pennington Formation on the Cumberland 

Plateau. Commonly, the green mudstone in these 

units is more clay-rich than the reddish to reddishpurple siltier mudstone and shale, and thus more susceptible to slope movement. Movements take place 

either in the colluvium or at the contact of the colluvium and weathered mudstone or shale. Slumpearthflows, debris slides, debris flows, earthflows, 

debris slide-earthflows, rock topples, and rock falls 

are the principal types of slope movement. Debris 

avalanches are not abundant, in part because of limited quantities of colluvium along the lower and middle parts of many slopes, especially in the western 

part of the Jackson County Mountains. Road widening and new highway relocations have triggered large 

numbers of slope movements along the west side of 

Sand Mountain. One new highway (Alabama 227) 

cuts across the lower part of an extensive colluvial 

slope in a direction roughly parallel to the prevalent 

orientation of nearly vertical joints. Above the highway cut, slumping and flowage at or near the base of 

colluvium overlying the Pennington Formation has 

been compounded by the dislodging of the thick-bedded sandstone bedrock of the Pottsville Formation, 

largely as a result of stress release. The fallen blocks 

have surcharged the already unstable slope. Springs 

emanating at the contact of permeable and impermeable bedrock contribute to the initiation of slope 

movement. 

In the Highland Rim section of northern Alabama, the movement-prone slopes are underlain by 

the Pride Mountain Formation of Late Mississippian 

age. The most susceptible material is plastic colluvial 

soil derived from grayish-green shale. Recent colluvial movements more than 1 00 m wide along gentle 

slopes, and prehistoric bedrock slumping along a 

northwest-trending joint-controlled valley attest to 

the long-term instability. 

Slope movements in the East Gulf Coastal 

Plain can be traced to failure surfaces in blue-gray 

and red to light-gray clay of the Tuscaloosa Group of 

Late Cretaceous age. Large slope movements northwest of Hamilton took place during and after construction of a major highway (U.S. 43). 

Summary 11 
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1 EXPLANATION I 

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Slope movement-prone area 

(based on presence of recent 

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B, Bangor Limestone 

PM, Pride Mountain Formation 

):> 
REFERENCES CITED 

Cotton, J. A., 1979, Soil survey of Marion County, Alabama: U.S. Soil Conservation Service in cooperation 

with Alabama Agricultural Experiment Station and Alabama Department of Agriculture and Industries, 1 00 

p, maps. 

Evans, R. S., 1981, An analysis of secondary toppling rock 

failures-the stress redistribution method: Quaternary 

Journal Engineering Geology, London, v. 14, p. 77-86. 

Fisher, S. P., Fanoff, A. S., and Picking, L. W., 1968, Landslides of southeastern Ohio: Ohio Journal of Science, 

v.68,no.2,p.65-80. 

Harris, W. F., Jr., and Causey, L. V., 1973, Geologic map 

of Marion County, Alabama: Alabama Geological Survey Map 104, scale 1: 125,000. 

Pomeroy, J. S., 1982a, Landslides in the Greater Pittsburgh 

region, Pennsylvania: U.S. Geological Survey Professional Paper 1229, 48 p. 

--1982b, Landslides and related features- Gadsden 

1 o by r sheet, Alabama-Tennessee: U.S. Geological 

. Survey Open-File Map 82-181, scale 1:24,000, 64 

sheets. 

Sapp, C. D., and Emplaincourt, Jacques, 1975, Physiographic regions of Alabama: Alabama Geological Survey Map 168, scale 1: 1 ,000,000, with text. 

Thomas, R. E., 1979, Landslides and related features -

Rome 1 o by 2° sheet, Alabama-Tennessee-Georgia: 

U.S. Geological Survey Open-File Map 79-944, scale 

1:24,000, 7 sheets. 

--1982, Landslides and related features - Rome 1 o 

by 2° sheet, Alabama-Tennessee-Georgia: U.S. Geological Survey Open-File Map 82-193, scale 1:24,000, 

9 sheets. 

Thomas, W. A., 1972, Mississippian stratigraphy of Alabama: Alabama Geological Survey Monograph 12, 121 

p. 

Varnes, D. J., 1978, Slope movement types and processes, 

Chap. 2, in R. L. Schuster and R. J. Krizek, editors, 

Landslides-analysis and control: Transportation Research Board Special Report 176, National Academy 

ofSciences, Washington, D. C., p. 11-33. 

References Cited 13