Hillslope processes and archaeology in Wadi Ziqlab, Jordan

Geoarchaeology: An International Journal, Vol. 13, No. 6, 595–616 (1998)q 1998 John Wiley & Sons, Inc. CCC 0883-6353/98/060595-22

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GEA(Wiley) RIGHT BATCH

Hillslope Processes and Archaeology in

Wadi Ziqlab, Jordan

John Field

Department of Geology, Western Washington University, Bellingham,

Washington 98225

E.B. Banning

Department of Anthropology, University of Toronto, Toronto, Ontario

M5S 1A1, Canada

Record levels of precipitation during February 1992 generated 290 earth flows and earthslumps in Wadi Ziqlab, Jordan. Geomorphologic and sedimentological characteristics of theselandslides and older colluvial deposits were used to identify the dominant mass-wasting pro-cesses active in the wadi. Earth flows in 1992 left long linear scars on the steep hillsides anddeposited thin, fine and coarse-grained, sheets on the well-developed colluvial slopes below.Older colluvial deposits exposed along the wadi bottom are crudely stratified, heavily biotur-bated, and contain paleosols, suggesting colluviation was episodic and occurred through aslow accumulation of successive earth flows. Earth slumps in 1992 produced crescenticscarps, flat benches, and thick colluvial masses; similar features preserved on the wadi slopeswere formed by the same process at an earlier time. Annual slope wash does not appearimportant on the steep, heavily landslide-scarred, slopes. The uneven distribution and epi-sodic occurrence of earth flows and earth slumps in Wadi Ziqlab have resulted in highlyvariable burial depths of archaeological material, as illustrated in one locality where Romanartifacts are buried over deeper than a Neolithic site only away. The ability of1 m 200 mearth flows to transport artifacts great distances has given rise to inverted stratigraphy oncolluvial slopes and has produced large artifact scatters located beyond the margins of thecolluvial slopes. These complex postoccupation disturbances and prehistoric land-use prac-tices would have been difficult to interpret without a full understanding of the hillslope pro-cesses active in Wadi Ziqlab and the landscape features they have produced. q 1998 John Wiley& Sons, Inc.

INTRODUCTION

Archaeological sites located on hillsides and adjacent colluvial slopes are ex-posed to a variety of processes capable of influencing site formation. Slow mass-wasting phenomena such as slope wash or creep can, over time, grossly disturbarchaeological context like more rapid landslide events (Waters, 1992). Identifyingthe processes and extent of colluviation in a given area is critical for analyzing thespatial distribution of artifacts and for developing survey and excavation strategies(Rick, 1976; Butzer, 1977; Wood and Johnson, 1978; Bowers et al., 1983; Gardnerand Donahue, 1985). For example, a single massive slump will not contain stratifiedcultural horizons like slope-wash deposits, and shallow test trenches may fail to

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intersect deeply buried archaeological material. While there are many examples ofhow slope processes have altered archaeological context (Butzer, 1971; Woods andJohnson, 1978; Waters, 1992), the full impact specific processes can have on ar-chaeological site formation is still poorly understood.

The exact mass-wasting process responsible for deposition of colluvial se-quences is often difficult to ascertain because these deposits are often massive,poorly stratified, and homogenized by bioturbation (Nelson, 1992). Landslideevents, when they occur, provide a unique opportunity to identify slope processesin the colluvial record by establishing links between observed processes and pre-served deposits. In February 1992, 290 landslides occurred in Wadi Ziqlab, Jordanas a result of record precipitation levels. A geomorphologic study of these land-slides in conjunction with a sedimentological and pedological analysis of relatedcolluvial deposits was used to assess the primary mass-wasting processes activein Wadi Ziqlab. Direct observations of the 1992 landslides and recognition of similarfeatures in the colluvial record has helped us discern the varying impact differentslope processes have had on site burial, artifact transport, and prehistoric land use.We hope the methods and criteria used to interpret the colluvial deposits and ar-chaeology of Wadi Ziqlab will find broader application in colluvial settings else-where.

SETTING

Wadi Ziqlab is a rugged tributary canyon of the Jordan River draining 2106 kmof the Ajlun highlands in northwestern Jordan (Figure 1). The wadi has erodedmore than below an extensive gently sloping, Tertiary erosion surface that250 mis underlain by Upper Cretaceous marls and bedded limestones (Fisher et al., 1966).Formed under the Mediterranean climate, thick, red, clay-rich Terra Rossa soilsare developed on this surface. Reworking of these soils has led to some secondaryaccumulations on the wadi slopes, particularly on more gently sloping benches(Fisher et al., 1966). The steep wadi slopes (367 average) are incompletely mantledby a thin fine-grained regolith developed from the weathering of the(5–10 cm)underlying marls. In the lower two-thirds of the drainage basin, colluvial slopesflank the base of the steep wadi (Figure 2). The colluvial slopes are smooth, con-cave-up surfaces best developed on the inside bends of the meandering wadi chan-nel. The colluvial surfaces slope perpendicular to the wadi bottom axis are up to

long from head to toe, and extend laterally for as much as along the200 m 400 mwadi slope. Similar colluvial slopes are not found in the upper drainage basin whereaverage slopes are much lower (227), the area is sometimes densely forested, andthe easily weathered marls are absent.

Archaeological research in Wadi Ziqlab began in 1981 with a surface survey bypedestrian transects of quadrats constituting a 20% random spatial sample21 kmof the drainage basin (Banning and Fawcett, 1983; Banning, 1985). This survey wasfollowed by systematic subsurface testing of colluvial slopes along the wadi bot-tom, which identified a number of sites and artifact scatters not detected during

LANDSLIDES IN JORDAN

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL 597

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Figure 1. Map of northwestern Jordan showing the location of Wadi Ziqlab.

the surface survey (Banning, 1996). Each “habitable” slope was subsampled withat least one trench, in area and normally deep; colluvial slopes larger1 3 3 m 2 mthan were sampled by two such trenches. In 1986, 1987, 1990, and 1992, a21000 mtotal of 18 trenches on 15 slopes were excavated. The most significant result of thesubsurface testing was the discovery of Tabaqat al-Buma (site WZ200; Figure 3), aLate Neolithic site (6700–6300 B.P.) underlain by a Kebaran lithics scatter (15,000–11,000 B.P.) (Banning et al., 1996). Although the five radiocarbon dates from bonein the Kebaran horizon are consistent with their stratigraphic order, the dates areyounger than published chronologies of the Kebaran (Bar-Yosef, 1970, 1975, 1981),suggesting that artifact transport may have occurred or that there was a consistentproblem with dating the bone. Regardless of potential dating problems, the sub-surface testing in Wadi Ziqlab confirmed suspicions that hillslope processes haddistorted the results of the surface survey. However, the types of processes re-sponsible for this distortion and their full impact on the wadi’s archaeology re-mained unclear.

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Figure 4(a). Large earth slump from 1992 on wadi bottom. This is a close-up of the earth slump seenin Figure 2. Note the steep crescentic scarp at the head of the slump, the gently sloping bench on top,and the thick colluvial mass blocking the main wadi bottom channel.

LANDSLIDES IN WADI ZIQLAB DURING 1992

Geomorphic Description of Landslides

Record amounts and intensities of precipitation from December 1991 to February1992 generated 290 landslides of varying size in the lower two-thirds of Wadi Zi-qlab’s drainage basin (Figures 2 and 3). The total number of landslides does notinclude numerous additional landslides closely associated with road construction.Sixty-four of the landslides were traversed by foot in June–July 1992, permittingclose inspection of features and accurate measurement of dimensions. The re-maining landslides were described from a distance, mapped on aerial photographs,and their size was estimated. The landslides were primarily of two types: rotationalearth slumps and translational earth flows (Figures 4[a] and 4[b]; Ritter et al., 1995;112–114). A small number of rockfalls and rockslides were also recorded.

Earth Slumps

The majority of the earth slumps occurred along the upper wadi rim in the thickclay-rich Terra Rossa soils. Other slumps formed in shallow slope “hollows” (asdefined by Reneau et al. [1990]), where runoff is concentrated and accumulationof reworked soils is greatest. The deep-seated, generally crescentic, slumps re-mained intact as they rotated away from the hillside (Figure 4[a]). The heads of



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the slumps are marked by transverse tension cracks and scarps that extend up tolaterally. The top surfaces of the displaced masses were tilted back, forming500 m

flat or gently sloping surfaces. The slump toes are oversteepened bulges on thewadi slopes that in several cases failed at the time of formation, spawning earthflows that moved downslope great distances.

Earth Flows

The earth flows stripped the thick loamy regolith that mantles the soft5–10 cmmarls, leaving narrow linear scars on the steep wadi slopes (Figure 4[b]). Fifteenpercent of the flows incorporated angular cobbles and boulders of unweatheredmarl exposed beneath the thin regolith. The flows were concentrated in hollows,but many flows also occurred on slope noses. The earth flows began as earth slideswith the regolith layer held intact by grass mats, as preserved just below some ofthe slide scars. This initial sliding caused the saturated material to break apart andflow downhill. Sixty percent of the earth flows did not reach the wadi bottom(Figure 2), and concentric and linear pressure ridges were preserved at the toe andflanks, respectively, of these more viscous flows. The characteristics of the morefluid earth flows that did reach the wadi bottom are discussed below with thesedimentological descriptions.

Sedimentological Description of Landslide Deposits

Earth Slumps

Although most of the slumps occurred high on the wadi slopes one slump didcome to rest on the wadi bottom, blocking the main channel and instantly depos-iting more than of sediment on the flanking colluvial slope (Figure 4[a]). This6 mthick colluvial mass is unstratified and displays no internal sedimentological struc-tures. Since the toe and flanks of the slump mass are very steep, the margins ofthe deposit are well defined, and the thickness of the deposit changes rapidly. Ifthe original parent material had contained sedimentary structures these structureswould likely have been rotated, disjointed internally with differential subsidence,and abruptly terminated at the slump margins.

Earth Flows

The characteristics of the earth-flow deposits that accumulated on the colluvialslopes in 1992 varied with the fluidity of the flow and the amount of bedrock rubbleincorporated in the initial slope failure. Earth flows transporting only fine-grainedregolith deposited a thin rectilinear sheet of sediment that was generally(,5 cm)not wider than the path of the earth flow on the slope above (Figure 4[b]). Theseflows rarely inundated the entire colluvial slope onto which they flowed. No internalsedimentary structures were observed in these thin sheets, but clean water flowingover some of the deposits later during the same storm washed away the fines andconcentrated coarse material along discontinuous drainage lines. Despite travel



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Table I. Sedimentological and pedogenic characteristics of the five stratigraphic units exposed alongthe floor of Wadi Ziqlab.

StratigraphicUnit

SoilHorizon

Thickness(cm) Color Texture Hardness

0 A1 0–11 10YR4/4 dark yel-lowish brown

Gravelly sandy silt Slightly hard

1 A2 30–50 10YR4/2 darkgrayish brown

Gravelly sandy silt Slightly hardto hard

Bw1 40–585 10YR4/4 dark yel-lowish brown

Gravelly sandy siltto silt

Slightly hardto hard

2 Bw2 0–124 10YR5/6 yellowishbrown

Sandy gravel Loose

3 2Bt .150 10YR3/3 darkbrown

Gravelly sandy silt Hard

2C 20 10YR4/4 dark yel-lowish brown

Gravelly sandy silt Slightly hard

4 3Bt 215–265 2.5YR3/4 dark red-dish brown

Sandy gravel Loose tovery hard

distances of up to down steep slopes, the earth flows were apparently not300 mtraveling with great force. The flows were impounded behind rock walls and ter-races on the colluvial slopes and flowed around olive trees, even saplings, withoutharm.

Deposits left by flows containing bedrock rubble left thin gravel sheets one ortwo cobbles thick on the colluvial slopes below (Figure 5). The most fluid flowswere associated with springs and spread out upon reaching the base of the hillleaving a thin gravelly fan-shaped sheet that covered the entire colluvial(,10 cm)slope. Very fluid earth flows sometimes extended beyond the toes of the colluvialslopes, depositing material along the wadi bottom and even up the opposite slope.

COLLUVIAL STRATIGRAPHY AND PEDOLOGY

The amount of sediment transported to the wadi bottom by the 1992 event rep-resents a very small fraction of the total volume of colluvium preserved in the lowertwo-thirds of the Wadi Ziqlab basin. Several natural exposures of colluvium andalluvium along the wadi bottom are more than thick. Pedological and sedi-6 mmentological investigations of these exposures have identified five interfingeringalluvial and colluvial units (Table I and Figure 6), their age constrained by buriedarchaeological material (Banning et al., 1996). The same stratigraphic units areobserved repeatedly in exposures beneath the colluvial slopes along the reach6 kmof Wadi Ziqlab between sites WZ120 and WZ200 (Figure 3).



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Soil Structure Soil CarbonateLower

BoundaryDepositionalEnvironment Archaeology

Age Estimate(yr B.P.)

Weak fine granu-lar

None Clear Colluvial None seen ,2000

Strong fine gran-ular

None Gradational Colluvial Roman tomodern

0–2,000

Weak coarsesubangularblocky

Thin coating onroot pores

Sharp to in-distinct

Late Neo-lithic

6500

Loose Thin filamentson cobbles

Sharp ero-sional

Alluvial None seen 6500–11,000

Moderate me-dium angularblocky

Root pores filled Gradual Colluvial Kebaran 11,000–15,000

Weak fine sub-granularblocky

None Clear

Loose to strongangular blocky

Thick coatingson cobbles

Erosionalon bed-rock

Alluvial None seen .15,000

Several features in the colluvium facilitated recognition of the mass-wasting pro-cesses responsible for deposition:

1. Units 0, 1, and 3 are poorly sorted generally unstratified deposits whichthicken rapidly towards the wadi slopes and are found beneath the concave-up colluvial slopes (Figure 6).

2. Thin stone lines and overlapping gravel lenses give rise to a crude stratificationin some exposures of Unit 1 (Figure 7).

3. The contact between Units 1 and 3, where present, records a 4500 year hiatusin deposition and is marked by a distinct change in soil structure, hardness,and pedogenic carbonate (Table I).

4. Large intact colluvial masses over thick occur isolated along the wadi4 mbottom and are unrelated to the five stratigraphic units found under the con-cave-up colluvial slopes.

MASS-WASTING PROCESSES RESPONSIBLE FOR COLLUVIATION

The characteristics of the colluvial deposits are consistent with deposition bythe same mass-wasting processes observed during the 1992 event. The thick iso-lated colluvial masses are similar in morphology and sedimentology to rotationalearth slumps. These deposits are associated with flat benches downslope of con-centric scarps, similar to the 1992 slumps (Figure 4[b]). The chaotic internal stra-tigraphy observed in some colluvial masses may have formed through differential

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Figure 6. Schematic cross section of colluvial and alluvial units exposed along the wadi bottom. Notto scale. See Table 1 for detailed unit descriptions. Note that the Late Neolithic horizon is buried moredeeply towards the wadi margin.

rotation of separate blocks during slumping and suggests that the masses wereformed by single depositional events.

The crude stratification observed in Unit 1, the hiatus between Units 1 and 3,and the presence of archaeological material throughout Units 1 and 3 are consistentwith deposition by a succession of earth flows. Gravel sheets deposited by earthflows in 1992 are similar to the gravel lenses in Unit 1 in terms of thickness andlateral extent (compare Figures 5 and 7). Although the homogeneous fine-grainedportions of Units 1 and 3 are too thick to be ascribed to a single earth flow, thecontacts between successive and overlapping flows would be difficult to identifyafter significant bioturbation and pedoturbation. The fresh colluvial deposits seenin Figure 4(b) have since been plowed into the older deposits below and a newolive grove planted. This is an exceptional example of the role humans can play inthe homogenization of multiple earth-flow deposits.

Annual slope wash does not appear to be a significant agent of colluvial depo-sition in Wadi Ziqlab. The effects of landslides, where they occur, far outweigh themass transport accomplished by continuous processes, especially on very steepslopes (Saunders and Young, 1983; Young and Saunders, 1986). Although gravellycolluvium can accumulate through annual slope wash (Kwaad, 1977), the thickness,geometry, and texture of gravel lenses in Unit 1 is more consistent with depositionby earth flows (Figures 5 and 7). Alternating coarse-grained and fine-grained col-luvial horizons have been ascribed to variations between rapid mass-wasting pro-cesses and slow annual slope wash, respectively (Nelson, 1992), but in Wadi Ziqlabthe abundance of coarse material appears related to the amount of unweatheredbedrock incorporated in the initial slope failure. Most of the 1992 earth-flow de-posits in Wadi Ziqlab were fine-grained and demonstrate that fine-grained colluvialdeposits are not exclusively the result of annual slope wash. Annual slope wash in



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Figure 8. Time sequenced schematic diagram illustrating the impacts landslides have had on artifacttransport and site burial in Wadi Ziqlab. Not to scale. (Time 0) Undisturbed Early Bronze age structuresare present on the wadi bottom while Roman and Late Neolithic artifact scatters are present at the topof the steep wadi slopes. Note the Roman and Late Neolithic artifacts buried to shallow depths onopposite sides of the wadi bottom. (Time 1) A landslide at Point A fills in wadi bottom channel fardownstream and transports Roman artifacts up the opposite slope to Point B. Artifacts transported bythis slide are deposited over Late Neolithic artifacts and other Roman artifacts buried along the wadibottom. If evidence for the landslide disappears, the transported nature of the Roman artifacts may gounnoticed since no stratigraphic inversion results. Sliding at Point C results in stratigraphic inversionbecause Late Neolithic artifacts are deposited above Early Bronze Age structures. (Time 2) Reestablish-ment of the wadi bottom channel obscures context of Roman artifacts transported up opposite slopeat Point B, resulting in the potential misinterpretation of the origin of the artifact scatter. Continuedsliding on the hillslope at Point D, perhaps because it is situated in a slope hollow, will result in deeperburial of Roman artifacts than older Late Neolithic artifacts buried on the opposite side of the wadibottom.



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Table II. Age and stratigraphic position of buried archaeological sites and artifact scatters discoveredduring subsurface testing of colluvial slopes.

SiteNumber Site Age Site Type

MaximumBurial Depth

StratigraphicPosition

WZ120 Neolithic (8200 B.P.) Site with structures 5 m Base of Unit 1WZ200 Late Neolithic (6500 B.P.) Site with structures 0.8 m Base of Unit 1

Kebaran (13,000 B.P.) Artifact scatter 2.5 m Unit 3WZ302 Roman (1600 B.P.) Artifact scatter 2.0 m Upper Unit 1WZ308 Roman (1600 B.P.) Artifact scatter 0.2 m Upper Unit 1Near WZ308 Roman (?) Single artifact 6.0 m Colluvial

massWZ310 Early Bronze I (4500

B.P.)Site with structures 2.0 m Lower Unit 1

WZ312 Roman (1600 B.P.) Artifact scatter 1.7 m Upper Unit 1

Wadi Ziqlab may be a more important process on hillslopes, concentrating sedimentin slope hollows before transport to the colluvial slopes below by subsequent earthflows and slumps.

IMPACT OF LANDSLIDES ON THE ARCHAEOLOGY OF WADI

ZIQLAB

The geomorphic and stratigraphic context presented above has helped interpretarchaeological findings in Wadi Ziqlab. Landslides in Wadi Ziqlab have had an im-pact on site burial, artifact transport, and prehistoric land-use decisions (Figure 8).

Site Burial

A number of archaeological sites and artifact scatters of different ages are buriedto widely varying depths below the colluvial slopes in Wadi Ziqlab (Table II). Ar-chaeological sites or portions of sites located at the heads of colluvial slopes areburied more deeply than sites lower on the same slope. For example, the LateNeolithic cultural horizon at Tabaqat al-Buma (site WZ200; Figure 3), stratigraphi-cally above the contact between Units 1 and 3, is buried near the head of90 cmthe colluvial slope but only near the wadi center (Figure 6). More dramatic20 cmvariations in burial depth result from slumping or a repeated concentration of earthflows in one area (Table II and Figure 8[D]). Late Neolithic structures at site WZ120,in the same stratigraphic position as at site WZ200, are buried beneath the5 msurface, and Roman pottery and glass at site WZ302 is buried deep only2 m

upstream of site WZ200 (Table II and Figure 3). Earth flows in 1992 occurred200 mless frequently on slope noses and where bedded limestones crop out. Over ex-tended periods of time significantly less colluvium will accumulate at the base ofslope noses, and archaeological sites, such as site WZ200, will be buried to shal-lower depths than even younger sites situated below slope hollows (Figure 8[D]).

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Figure 9. Overview of excavations on the colluvial slope at Tabaqat al-Buma (site WZ200) showing wellpreserved stone walls of Late Neolithic homes. A clay lined silo in rock wall, reused as a grave, is visiblejust to the right of the two standing men in the center of the photograph.

Despite the shallow burial depth, Late Neolithic structures and living surfacesare pristinely preserved at site WZ200 (Figure 9; Banning et al., 1996). Earth flowshave the potential to damage (Folk, 1975) or preserve archaeological sites (Kirkand Daugherty, 1978), depending on the composition and force of the flow. The1992 earth flows in Wadi Ziqlab caused very little damage as they filled behind rockwalls and flowed around the bases of olive saplings with little damage. Unlike theOzette site in Washington State that was buried by a single large mud flow (Kirkand Daugherty, 1978), preservation at site WZ200 and other sites in Wadi Ziqlaboccurred through a succession of earth flows over an extended period of time.Assuming the landslides in 1992 represent a typical event in Wadi Ziqlab, a singleearth-flow deposit with a thickness of would not be capable of obscuring a10 cmsite. The presence of nearly horizontal stone lines above the Late Neolithic horizonat site WZ200 indicates that site burial did result from multiple landslide events.

Artifact Transport

Three of the 64 closely inspected landslides transported archaeological artifacts.One large earth flow transported hundreds of artifacts downslope from a100 mhilltop site, across the narrow tributary bottom at the foot of the slope, up the5 mopposite side, and down the tributary bottom (see Figure 8[A] and 8[B]).300 mThe pottery and glass shards remained unabraded, in contrast to artifacts trans-



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ported the same distance by streamflow (Skibo and Schiffer, 1987). The context ofartifact transport will eventually be lost over several years as evidence for the earthflow fades and the wadi bottom channel becomes reestablished (see Figure 8). Adiffuse scatter of unabraded artifacts will remain however, far removed from theirprimary context. Spatial analysis plays an integral role in cultural reconstructionsof archaeological sites, so significant displacements of artifacts by natural pro-cesses must be identified before analyzing artifact distributions (Rick, 1976; Bowerset al., 1983). Distinguishing between fine-grained earth-flow deposits and similarlooking annual slope-wash deposits is critical, because earth flows, unlike slopewash, have the potential to move artifacts beyond the colluvial environment wherethe possibility of misinterpreting artifact distributions is much greater. Folk (1975)documented the destruction and burial of a large Byzantine building by an earthflow that originated from the opposite side of the valley.

At site WZ310 (Figures 4[a] and 4[b]), in situ Early Bronze I structures and pitsdated between 4600 and 4400 B.P. are found beneath deposits containing numerousLate Neolithic artifacts (Banning, 1996). Bioturbation or invasive excavation of thepits are unlikely causes of this stratigraphic inversion, since no Neolithic structuresor artifacts are found below the Early Bronze I deposits. Mass wasting appears alikely cause of the inversion (see Figure 8[C]), as site WZ310 is situated on a col-luvial slope at the base of a heavily scarred hollow. No in situ Late Neolithicstructures are found at the site, and artifacts, albeit undiagnostic, are found on thehillslope above. Stratigraphic inversion and mixing of cultural horizons by masswasting was envisioned by Butzer (1982) and Waters (1992), but has rarely beendocumented (Hopkins and Giddings, 1953; Zotz, 1956).

Prehistoric Land Use

Landslides in Wadi Ziqlab have clearly affected site formation after site aban-donment, but did landslides also affect land use decisions during habitation? Ex-tensive flat benches high on the wadi slopes were formed by large rock slumps thatprobably predate the oldest recorded archaeological site in Wadi Ziqlab (Figure10). Today, these hillslope benches and the colluvial slopes along the wadi bottomare used for pasture, olive and pomegranate groves, the cultivation of grains andvegetables, and human habitation (Figure 10). The new olive grove planted on acolluvial slope after earth-flow deposition in 1992 underscores the important rolemass wasting plays in land-use decisions (Figure 4[b]). The Late Neolithic home-stead at site WZ200 and the associated artifact assemblage containing abundantflint sickle blades, pottery, and bones of sheep or goats suggests that prehistoricinhabitants also made use of landslide-formed landscape elements (Figure 9; Ban-ning et al., 1994, 1996).

The colluvial slopes are ideal places for habitation as they are close to springs,reeds, and other streamside resources while high enough to avoid most wadi bot-tom floods. No certain Late Neolithic sites were recorded in Wadi Ziqlab during asurface survey of the uplands and wadi bottom (Banning and Fawcett, 1983), but

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Figure 10. Large, prehistoric, deep-seated bedrock slump feature displaying gently sloping bench withscarp just upslope. Note olive and pomegranate groves on surface of flat bench.

several significant Late Neolithic sites were discovered after systematic subsurfacetesting of the colluvial slopes. Colluviation can bias the results of archaeologicalsurveys by obscuring sites that are situated in favored areas of settlement (Alba-nese, 1978; Gardner and Donahue, 1985; Banning, 1996). Without subsurface test-ing, the Late Neolithic occupation of Wadi Ziqlab would have gone completelyunnoticed.

CONCLUSIONS

Although heavy bioturbation and pedoturbation have homogenized the colluvialdeposits in Wadi Ziqlab, recognition of depositional processes was possible byusing both geomorphic and sedimentological features (Table III). Large earthslumps in Wadi Ziqlab are often associated with flat benches and concentric headscarps (Figure 4[a]) while earth-flow deposits occur on concave-up colluvial slopes(Figure 4[b]). The fine-grained colluvial deposits in Wadi Ziqlab are very similar toannual slope-wash deposits, and before the insights learned from the 1992 landslideevent were interpreted as such. The 1992 event revealed that earth-flow depositscan be both fine grained (Figure 4[b]) and coarse grained (Figure 5), producingcrude stratification at a single point through time (Figure 7).

Identifying the specific mass-wasting processes operating in a given setting is



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FIELD AND BANNING

614 VOL. 13, NO. 6

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critical at all stages of archaeological research. During surface surveys, archaeol-ogists must remain cognizant that earth flows can instantly transport artifacts muchfurther than years of slope wash. Artifacts transported beyond the foot slope en-vironment by earth flows, including up the opposite slope (Figure 8[B]), could bemistakenly recorded by archaeologists as a distinct site or as an artifact scatterthought to originate from another source. Since archaeological sites are commonlydisturbed by slope processes and buried in mass-movement deposits (Waters, 1992;Goldberg and Bar-Yosef, 1995), subsurface testing of colluvial slopes is essentialto determine the representativeness of site distributions recorded by surface sur-veys. Results from Wadi Ziqlab demonstrate the need for a subsurface testing strat-egy based on stratigraphic position rather than absolute burial depth. For example,excavations targeting Late Neolithic sites in Wadi Ziqlab do not need to go deeperthan the contact between Units 1 and 3, regardless of whether the contact is

or beneath the surface. Additionally, shallow burial of an old site does30 cm 5 mnot preclude the possibility that younger material nearby could be encountered ata greater depth (Table II and Figures 3 and 8). Cultural reconstructions during thelast phases of archaeological research not only depend on a full understanding ofpostoccupation disturbances but also on an understanding of how natural pro-cesses affected prehistoric land-use decisions. In Wadi Ziqlab, landscape elementsformed by landslides were and still are preferred locations for settlement and ag-riculture (Figures 9 and 10). Settlements on colluvial slopes are prone to burial,potentially obscuring all evidence for cultures preferring these environments (e.g.,Late Neolithic settlements in Wadi Ziqlab).

Landslides in Wadi Ziqlab have had a significant impact on archaeological siteburial, artifact transport, and land use. While the impact of mass wasting on ar-chaeological resources is well documented (Butzer, 1971; Woods and Johnson,1978; Waters, 1992), Wadi Ziqlab provides a lucid example of how pervasive theseimpacts can be in a single locality (Figure 8). The complex archaeological associ-ations in Wadi Ziqlab resulting from uneven burial depths, stratigraphic inversion,and distant transport of artifacts underscore the need for more detailed geomorphicand sedimentological studies of colluvial deposits. If the specific mass-wasting pro-cesses active in Wadi Ziqlab had not been identified by linking processes observedin the 1992 landsliding event with characteristics preserved in the older colluvialdeposits, the full nature and extent of archaeological impacts would have goneunnoticed.

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Received February 1, 1997

Accepted for publication March 30, 1998

Documents

Hillslope processes and archaeology in Wadi Ziqlab, Jordan