Journal of Coastal Research
20
4
980–999
West Palm Beach, Florida
Fall 2004
Stratigraphy of Back-Barrier Coastal Dunes,
Northern North Carolina and Southern Virginia
K.G. Havholm†, D.V. Ames‡, G.R. Whittecar§, B.A. Wenell†1, S.R. Riggs‡, H.M. Jol†, G.W. Berger*,
and M.A. Holmes†2
†Departments of Geology and
Geography
University of Wisconsin-Eau
Claire
Eau Claire, WI 54702, U.S.A.
‡Department of Geology
East Carolina University
Greenville, NC 27858, U.S.A.
§Department of Ocean, Earth
and Atmospheric Sciences
Old Dominion University
4600 Elkhorn Ave.
Norfolk, VA 23529, U.S.A.
*Quaternary Sciences Center
Desert Research Institute
2215 Raggio Parkway
Reno, NV 89512, U.S.A.
ABSTRACT
HAVHOLM, K.G.; AMES, D.V.; WHITTECAR, G.R.; WENELL, B.A.; RIGGS, S.R.; JOL, H.M.; BERGER, G.W., and
HOLMES, M.A., 2004. Stratigraphy of back-barrier coastal dunes, northern North Carolina and southern Virginia.
Journal of Coastal Research, 20(4), 980–999. West Palm Beach (Florida). ISSN 0749-0208.
Ground penetrating radar studies of four representative active back-barrier dunes, combined with radiocarbon and
photon-stimulated-luminescence dating techniques and soils analysis, reveal phases of alternating dune activity and
stabilization along the North Carolina–Virginia coast. Two smaller dunes represent only the current phase of dune
activity. Two larger dunes preserve evidence of three phases of dune development (ca. 740, 1260 and 1810 AD) and
intervening phases of soil development. Climate, particularly moisture conditions, played a part in the timing of dune
activity and stabilization events. All three dune phases are associated with drier conditions whereas soils formation
is associated with humid conditions. Modern (phase 3) dunes are more widespread along the coast and their formation
is attributed to a combination of dry conditions, increased storminess associated with the Little Ice Age, and rising
sea level. Tidal inlet closing and storm overwash processes likely provided sediment point sources for individual dune
masses. The longer history and much greater volume of dune sand in the area of the two larger dunes suggests a
greater sediment supply in this locality.
ADDITIONAL INDEX WORDS: Ground penetrating radar, coastal dune, dune reactivation, dune stabilization, paleosol, luminescence dating, radiocarbon dating, Little Ice Age.
INTRODUCTION
Coastal dune formation is episodic, and variable in location, style and extent of development due to the interaction
of terrestrial, atmospheric, and near-shore ocean systems. In
humid coastal regions, vegetation plays a significant role in
dune development (e.g., GOLDSMITH, 1989). In the last two
decades researchers have begun to develop descriptive and
predictive models to explain patterns of coastal dune development and preservation (e.g., PSUTY, 1988). Foredunes,
which form in situ as a result of trapping of sand by vegetation and do not migrate (impeded dunes, PYE, 1983), have
received the most attention because of their role as frontline
protection from wave attack during storms. Models have been
developed to describe conditions favoring foredune formation
and stages of foredune development (e.g., HESP, 1988; PSUTY,
1988, 1993; KNIGHT et al., 2002). Dunes that actively migrate
inland or along the coast, typically over vegetated terrain
(‘‘transgressive dunes,’’ GARDNER, 1955; PYE, 1983), have received less attention. General conceptual models to explain
or predict where, when, why and in what form dunes transgress inland, especially in non-arid regions, are still in a na03503A2 received and accepted in revision 10 April 2003.
1
Current address: 2524 W. Twin Lakes Rd., Mausou, IA 50563.
2
Current address: Hydrology Division, Arizona Dept. of Water Resources, 500 N. 3rd St., Phoenix, AZ 85004.
scent stage (ORME, 1988; HESP and THOM, 1990). (Because
the term ‘‘transgressive’’ can be confused with marine transgression in a coastal setting, the term ‘‘back-barrier dunes’’
is used here, although it is an imperfect substitute because
such dunes also form on coasts without barrier islands or
spits.)
If models of back-barrier dune development in humid coastal regions are to be enhanced, more data are needed on how
such dunes develop in time and space. A growing body of
literature includes earlier, primarily descriptive studies (e.g.,
BROTHERS, 1954; COOPER, 1958) and a second generation of
studies using radiocarbon and, later, luminescence dating
techniques to develop dune event chronologies (e.g., PYE and
RHODES, 1985; SHULMEISTER and LEES, 1992; THOM et al.,
1994). Ground penetrating radar (GPR) now allows non-destructive imaging of internal dune stratigraphy that was previously inaccessible, beginning a new generation of dune
studies in both desert dunes (BRISTOW et al., 1996; BRISTOW
et al., 2000a), and coastal dunes (foredunes: e.g., JOL et al.,
1998; BRISTOW et al., 2000b; back-barrier dunes: e.g., CLEMMENSEN et al., 1996).
The main contribution of this study is to integrate GPR and
optical luminescence techniques with trenching, radiocarbon
dating, and soil analysis to develop a chronology of back-barrier dune formation and stabilization in a humid coastal region where no such study has previously been done (Figure
Coastal Dune Stratigraphy
981
Table 1. Ground penetrating radar systems and methods.
System
Transmitter
(volts)
Antennas
(MHz)
Antenna
spacing
(m)
Shot point spacing
(mm)
Topographic
correction
Post-processing
PulseEKKO
SIR System-2
1000
1200
100
100
1.0
1.45
0.5 (hand-held)
;8 to 9 (vehicle-transported)
Total survey station
2-ft. contour topo. map
AGC
Filtering, AGC, Trace stack
a
b
a
b
Sensors and Software, Inc.
Geophysical Survey System Inc.
1). Defining a dune chronology constrains the field of possible
controls on dune activity. As such studies continue on various
coasts, emerging patterns should lead to development of more
general models of coastal dune development and stabilization.
The study supports two additional objectives. The chronology of eolian processes, integrated with ongoing studies of
regional coastal development through time (e.g., SAGER and
RIGGS, 1998), provides a more complete understanding of
coastal sedimentary processes. Finally, the number and size
of active dunes in the study area has been steadily decreasing
since the 1930’s (e.g., ALBERTSON, 1936; BIRKEMEIER et al.,
1984) and the value of saving the remaining dunes for economic, ecologic and aesthetic reasons is now recognized. At
the same time, continued migration of dunes causes problems
in urban areas. An understanding of dune history can inform
management decisions for coastal dune lands that must be
made by national and state park systems, municipalities, and
private landowners.
SETTING
The dunes examined in this study are within the Albemarle
embayment, one of a series of broad structural embayments
along the coastal plain of the eastern U.S. (TRAPP, 1992). The
axis of the Albemarle embayment parallels Albemarle Sound
(Figure 1a). This embayment preserves a complex package of
Pleistocene and Holocene marine, estuarine and barrier sediments (RIGGS et al., 1992, 1995). The Quaternary sediments
overlie a passive margin shelf sequence composed primarily
of Cretaceous and younger sedimentary units overlying older
basement rocks (e.g., GOHN, 1988).
During glacial sea-level lowstand coastal rivers such as the
Roanoke, now a trunk stream flowing into Albemarle Sound,
incised valleys and delivered fluvial sediment across the exposed shelf (Figure 1c). As sea level rose in the Holocene,
channels were flooded and back-filled with sediment (S AGER
and RIGGS, 1998). Limited sand supply in the coastal system,
in combination with micro-tidal conditions, have developed a
classic wave-dominated barrier from Cape Henry to Cape
Hatteros with one modern inlet (Davis, 1994). Historically
and prehistorically, a number of inlets have opened and
closed in this area (FISHER, 1962; Figure 1d). The sand barrier is narrow (0.5–2 km) except where flood deltas formed
at sites of past inlets or in areas where large sediment supplies allowed for the formation of extensive beach ridge sequences such as in the Kitty Hawk Woods, Nags Head Woods,
and Colington Island (FISHER, 1967). The local abundance of
sand that supplied shoreline progradation in this area may
be related to the presence of paleo-Roanoke riverine sediments on the inner shelf. However, for the past century,
much of this part of the Atlantic coastline has been generally
erosional, judging from the lack of foredunes and the ongoing
erosion of foredunes constructed in the 1930’s (BIRKEMEIER
et al., 1984).
This region has sufficient rainfall (110 cm/year at Duck,
1978–1996 avg., BARON, 1999) to support lush vegetation in
the oak-hickory-pine ecological zone (BURK, 1962; GODFREY,
1976). Precipitation from mid-latitude cyclones in winter and
convection and tropical depressions in summer distributes
the rainfall fairly evenly throughout the year (BARON, 1999;
LEFFLER et al., 1992). The harsh conditions associated with
barrier islands, such as salt spray, blowing sand, and frequent overwash, limit development of mature vegetation successions (e.g., OOSTING and BILLINGS, 1942; GODFREY and
GODFREY, 1976). Active dune surfaces on the Outer Banks
typically support salt- and sand-tolerant species such as sea
oats (Uniola paniculata) and panic grass (Panicum amarum).
The typical succession for surfaces more than 1.5 m. above
the water table and where salt spray is not a factor, is to
shrubs and trees including live oaks (Quercus virginiana), juniper (Juniperus virginiana), and loblolly pines (Pinus taeda;
BURK, 1962; FROST, 1999; STALTER, 1993).
Winds blow from all directions, but sand-moving winds
from the north and northeast predominate in the winter
months. From May through August, sand-moving winds from
the southwest quadrant equal and sometimes exceed those
from the northeastern quadrant (BARON, 1999; LEFFLER et
al., 1992). However, yearly averages suggest that strong
winds from the north and northeast are more frequent, resulting in greater sand transport to the south and southwest
(Figure 1b). Most of the strongest winds result from extratropical cyclones, or ‘‘Nor’easters’’, which are most common
from October to March (DOLAN et al., 1988). Less frequently,
tropical depressions or hurricanes affect the area during summer and fall; wind patterns from these depend on the track
of the system relative to the coast.
METHODS
Dune Interior Imaging
Ground penetrating radar (GPR) was used to image the
internal stratigraphy of the dunes. Surveys were performed
with two different systems and techniques (Table 1). Twoway travel-time was translated into depth below the surface
Journal of Coastal Research, Vol. 20, No. 4, 2004
982
Havholm et al.
Table 2. Radiocarbon ages.
Sample number
Sample locality
and type
Conventional
radiocarbon age
(yrs. BP)a
Calibrated
radiocarbon age
(yr. AD)b
40 6 60
1690–1730
1810–1920
Modern
1710
1865
PS2
1670–1780
1795–1945
1695–1725
1815–1920
1655–1890
1905–1950
1725
1870
1710
1868
1773
1928
PS2
1520–1570
1630–1890
1905–1950
1650–1890
1910–1950
1650–1950
1655–1950
1650–1950
885–1285
1260–1410
980–1025
1545
1760
1928
1770
1930
1880
1803
1800
1085
1335
1003
PS2
Mean calibrated age
(yr. AD)c
Buried soil
Run Hill
RH 97-1
RH 98-1
In situ stump
Inner wood of tree
In situ stump
Outer wood of tree
In situ stump
RH 98-2
In situ stump
RH 98-3
Wood fragment
180 6 40
JR 96-1
Soil organics with charcoal
220 6 60
JR 97-1
In situ stump
170 6 50
JR
JR
JR
JR
JR
JR
In situ stump
Soil organics
Wood
Charred wood
Charred wood
Soil organics
RH 97-2
0
100 6 50
30 6 50
PS2
PS2
Jockeys Ridge
98-2
10-U (AMS)
98-4
98-5 (ext. ct.)
98-3
10-L (AMS)
160
220
130
950
670
1030
6
6
6
6
6
6
60
40
70
110
60
50
PS2
PS2
PS2
PS2
PS1
PS1
PS1
Analytical error of 1 sigma.
Calibration error of 2 sigma.
c
Calibration: STUIVER and LONG, 1993.
a
b
by measuring near-surface velocity of the electromagnetic
pulses through the substrate with a ‘‘common mid-point’’ survey (JOL and SMITH, 1991). At Jockeys Ridge the same value
(0.14m/ns) was used everywhere. A global positioning system
(GPS) was used to locate all transects accurately. Most major
reflections imaged by GPR were ground-truthed on each dune
by sampling in outcrop, in a trench, or with an auger.
Dating
Two methods of dating, radiocarbon and luminescence,
were used in the project (Tables 2, 3). Ages of in situ tree
stump remains (typically outer tree rings) and/or loose wood
fragments from each buried soil exposure were obtained using standard radiocarbon methods (Beta Analytic Inc.). Soil
organic material from two buried soils was analyzed with the
Table 3. Photon-stimulated-luminescence ages from quartz.
Sample locality
Penney Hill PEH97-1
Run Hill 1 (upper) RNH97-5
Run Hill 2 (lower) RNH97-1
Jockeys Ridge 1 (upper) JRDG95-1
Jockeys Ridge 2 (middle) JKR97-1
Nags Head Woods (Tr. 8) NHW95-12
Nags Head Woods (Tr. 2) NHW95-4
a
Agea
(yrs. BP)
143
108
1232
187
742
1037
826
6
6
6
6
6
6
6
Age
(yr. AD)
ca.
ca.
ca.
ca.
ca.
ca.
ca.
16
11
65
15
51
60
69
Analytical errors are 1 sigma. Analysis year is 1999.
1855
1890
765
1810
1260
960
1175
Dune
Phase
DP3
DP3
DP1
DP3
DP2
AMS radiocarbon method. Tree-death age provides a minimum age for buried soil development and an approximate age
for the reactivation of the dune that buried the tree.
Photon-stimulated-luminescence (PSL, AITKEN, 1998) dating of 125–212 mm diameter quartz and potassium feldspar
sand grains was applied to determine the age of last exposure
to sunlight, representing dune activity. Quartz and feldspar
grains behave as paleodosimeters. Luminescence intensity,
measured on sand collected in light-tight tins, is proportional
to the total absorbed ionizing radiation dose since burial. Divided by the radiation dose rate, this luminescence-derived
post-burial dose yields a PSL age. Samples were collected in
trenches from buried dune strata at depths of 0.5 to 1.5 m
(see BERGER et al., 2003, Figure 2 for details of collection
sites). The radiation dose rate for the environment of each
sample was calculated from measurements of concentrations
of potassium, uranium and thorium in the sand, combined
with estimates of local cosmic-ray dose rates. Because of low
feldspar concentrations in the dune sand (BERGER et al.,
1996), quartz ages are reported here. The PSL from quartz
was stimulated by intense, restricted-wavelength blue (470
nm) diode light. Single-aliquot-regeneration procedures
(MURRAY and WINTLE, 2000) were employed for quartz. Further details of methods and results are given in BERGER et
al. (2003).
Soils Analysis
Buried soils were described in shallow pits and outcrops
using terminology and procedures outlined in SCHOENEBER-
Journal of Coastal Research, Vol. 20, No. 4, 2004
Coastal Dune Stratigraphy
Table 4. Buried soil descriptions for Run Hill and Jockeys Ridge.
Horizon
Description
Ab
Eb
Bbw
C
dune sand several meters thick; 10YR7/1 light gray finemedium sand, cross-bedded; clear, wavy boundary
0–8 cm; 10YR3/1 very dark gray sand with 10YR7/1 light
gray sand in irregular lenses; loose moist, slightly hard
dry; greatest concentration of humus in center of horizon; clear wavy boundary
8–13 cm; 10YR7/2 light gray sand; loose moist, loose dry;
clear to gradual wavy boundary
13–21 cm; 10YR7/4 very pale brown sand; loose moist,
weakly coherent dry; numerous burrows, 10YR7/2 light
gray sand; gradual to diffuse boundary
211 cm; 10YR8/3 very pale brown sand; loose moist, loose
dry; cross-bedded dune sand
b. Location: Upper buried soil (PS2) Site JR04, Jockeys Ridge, Dare
County, N.C. (UTM 18 S 0442552, 3980019) Paleoslope position: footslope
C2
Ab
Bb
C1b
C2
dune sand several meters thick 10YR7/1 light gray finemedium sand, cross-bedded; abrupt wavy boundary
0–18 cm; 10YR3/1 very dark gray sand; loose moist, weakly coherent dry; gradual wavy boundary
18–36 cm; 10YR5/4 yellowish brown sand; loose moist;
weakly coherent dry; clear wavy boundary
36–60 cm; 10YR8/3 very pale brown sand; loose moist,
loose dry; gradual wavy boundary
601 cm; 10YR8/2 white sand; loose moist, loose dry; crossbedded dune sand
c. Location: Upper buried soil (PS2) Site JR05, Jockeys Ridge, Dare
County, N.C. (UTM 18 S 0442550, 3980102) Paleoslope position: concave lower side slope
C
Oib/Ab
Eb
Bb
C1b
C2
dune sand several meters thick; 10YR8/1 white fine-medium sand, cross-bedded; abrupt smooth boundary
0–3 cm; 10YR4/1 dark gray sand with irregular lenses of
10YR3/1 very dark gray fibrous peat, 0–3 cm thick; burrows filled with 10YR7/1 light gray sand; loose moist,
weakly coherent dry; clear wavy boundary
3–10 cm; 10YR7/1 light gray sand; many fine weak lamellae (,1 mm thick) 10YR4/6 spaced 1–3 cm; clear wavy
boundary
10–18 cm; 10YR6/4 light yellowish brown sand; loose
moist, weakly coherent dry; clear irregular boundary
18–50 cm; 10YR7/3 very pale brown sand with 10YR8/3
krotovina and root traces; loose moist, loose dry; clear
wavy boundary
501 cm; 10YR8/2 very pale brown sand; loose moist, loose
dry; cross-bedded dune sand
d. Location: Lower buried soil (PS1) Site JR05, Jockeys Ridge, Dare
County, N.C. (UTM 18 S 0442545, 3980125) Paleoslope position: toeslope
C
Ab
A/Eb
Bb
Table 4. Continued.
Horizon
a. Location: Buried soil (PS2) Site RH01, Run Hill, Dare County, N.C.
(UTM 18 S 0439525, 3984325) Paleoslope position: shoulder
C
983
dune sand several meters thick; 10YR8/1 white fine-medium sand, cross-bedded; common abrupt wavy dark yellowish brown lamellae 10YR4/6 (1–3 mm thick) in lower
10 cm; gradual wavy boundary
0–10 cm; 10YR4/2 dark grayish brown sand with irregular
patches 10YR6/2 light brownish gray; loose moist, loose
dry; common abrupt wavy 10YR4/6 dark yellowish
brown lamellae (1–3 mm thick); gradual wavy boundary
10–50 cm; 10YR5/2 dark grayish brown sand with large
irregular patches of 10YR7/3 very pale brown and
10YR8/1 white sand; loose moist, loose dry; common
abrupt wavy 10YR4/6 dark yellowish brown lamellae
(1–3 mm thick) in upper 20 cm, 1–2 mm thick in lower
20 cm; diffuse wavy boundary
50–80 cm; 10YR8/3 very pale brown sand; loose moist,
weakly coherent dry; diffuse wavy boundary
C1b
C2
Description
80–100 cm; 10YR7/3 very pale brown sand with 10YR8/3
krotovina and root traces; loose moist, loose dry; clear
wavy boundary
1001 cm; 10YR8/2 very pale brown sand; loose moist,
loose dry; cross-bedded dune sand
GER et al. (1998; Table 4). They can be distinguished from
less well developed dune surface soils that contain A–C profiles, with very weak color change due to iron stripping just
below the litter (O) layer. By using outcrop patterns and
hand-auger holes to physically trace soil surfaces from an exposure to the nearest GPR transect, and from there throughout the area, buried soil units were determined to be identifiable and laterally continuous and therefore useful as stratigraphic markers.
DUNE MORPHOLOGY AND HISTORICAL DATA
The active back-barrier dunes of this study (Figure 1d) lie
1 km or less from the Atlantic coast and are simple crescentic
forms with the exception of Run Hill (Figure 2a), which is a
compound crescentic dune (MCKEE, 1979). Jockeys Ridge is
a group of 4 dunes (Figure 2b). The two study dunes to the
north (Penney and Snow Hills) are significantly smaller overall than the two southern dunes and maximum dune height
increases for all dunes from north to south (13 to 27 m). Snow
Hill, Penney Hill and the highest Jockeys Ridge peak have
decreased in height since the mid-1970s (GUTMAN, 1977b;
GOLDSMITH, 1977; JUDGE et al., 2000). The dunes are transverse (HUNTER et al., 1983), with major slipfaces on their
southern side and a southerly migration direction, approximately parallel to the net sand transport direction (Figure
1b).
Limited migration data are available for these dunes. Snow
Hill moved southward 1.5 m/yr in the 1970’s with temporary
slipfaces moving eastward (GUTMAN, 1977a,b). Comparison
of an 1851 map and a modern map (1982) suggest a longterm migration rate for Run Hill of about 7 m/yr (Figure 3).
A time series of aerial photos from 1952 to 1996 shows a
significant decrease in migration rate between 1970 and 1982
as vegetation and urbanization of the area to the north and
east of the dune progressed (HOLMES et al., 1997; Figure 4a).
During three years of stake monitoring (1995–1997) various
parts of the main slipface of Run Hill migrated from 0 to 0.75
m/yr. while parts of superimposed dunes moved eastward at
rates up to 1 m/yr (WEAVER et al., 1997). Long-term rate of
movement of Jockeys Ridge dunes can’t be determined from
the map comparison because specific dune masses can not be
identified on the 1851 map (Figure 3). The southern-most
Jockeys Ridge dune was monitored after sand removal and a
4-month healing period in early 1995. The slipface migrated
at an average rate of 0.3 m/mo (3.6 m/yr) until a series of
storms in 1999 caused rapid movement, giving a ;5-year average of nearly 0.5 m/mo (6 m/yr; Figure 4b). All of the study
Journal of Coastal Research, Vol. 20, No. 4, 2004
984
Havholm et al.
Figure 1. Location and setting of the study dunes. a. Regional map. b. Sand transport rose, calculated from wind data collected at Duck, N.C. from 1980
to 1991 using the method of FRYBERGER (1979). Length of rose ‘‘petals’’ show proportion of potential sand drift in each direction in percent of total sand
drift in all directions. c. Location of Roanoke River paleo-river system (modified from R IGGS et al., 1992). d. Map showing locations of four study dunes,
other dunes in the region, and locations mentioned in text. Ovals indicate active dunes, squares indicate stabilized dunes. Black arrows point to locations
of relict tidal inlets (FISHER, 1962). 1. Unnamed prehistoric inlet 2. New Currituck Inlet.
dunes are migrating over variably vegetated landscapes including grasses and herbs, shrubs and scrub trees. Portions
of Run Hill dune are overrunning a mature maritime forest
developed on the stabilized Nags Head Woods dune field (Figure 2a).
Penney Hill and Jockeys Ridge are essentially unvegetated
and have simple cuescentic shapes (Figures 2b, 5c). Both
Snow Hill and Run Hill are partially vegetated with grasses
and shrubs that are slowing the migration of their upwind
stoss components and beginning their transformation from
crescentic to parabolic forms (Figures 4a, 6c). Dunes just to
the south of Snow Hill have already converted to parabolic
forms as a result of the reduction in sediment availability
since the initial construction in the 1930’s of artificial foredunes along the coast (HENNIGAR, 1977; GUTMAN, 1977a).
Earlier claims that the area around Snow Hill was a ‘‘vegetated paradise’’ prior to deforestation after the civil war (e.g.,
COBB, 1906, quoted in HENNIGAR, 1977) are disputed in more
recent vegetation studies (FROST, 1999; DOLAN and LINS,
1986; GODFREY and GODFREY, 1976; DUNBAR, 1958).
Level of traffic on the dunes varies. Snow Hill has virtually no foot traffic, whereas Jockeys Ridge is trampled by
over a million visitors per year. Penney Hill experiences significant vehicular traffic. Although driving on Run Hill has
been officially prohibited since the early 1990s, continued
vehicular activity has maintained roads cut through vegetated portions of the dune and sand movement occurs along
these trackways. A portion of Run Hill was mined from 1980
to 1989 forming a scarp that is now migrating eastward
(Figure 4a).
Journal of Coastal Research, Vol. 20, No. 4, 2004
Coastal Dune Stratigraphy
985
DUNE STRATIGRAPHY
Snow Hill and Penney Hill
GPR reveals that the two smaller northern dunes each
comprise one package of predominantly high-angle reflections (up to 10 m thick, Snow Hill; 12 m thick, Penney Hill),
interpreted as dune strata (Figures 5, 6). The high-angle reflections overlie a package of sub-horizontal reflections, interpreted as the pre-dune barrier stratigraphy. Dune strata
are predominantly foresets formed by migration of the dune
lee-slope to the SSW. Coarse variation in reflection dip angle
represents GPR sampling of strata formed by different leeslope components (slipface vs. non-slipface, different lee-face
orientations). More subtle changes in dip orientation and minor truncations of reflections represent minor modifications
of lee-slope shape resulting from shifts in wind direction (e.g.,
bounding surface, position 140–168, Figure 5a). Near the
dune crests, dune topsets that formed on the gentle slope
between the dune crest and brink are preserved (e.g., position
140, Figure 6a; position 160, Figure 5a). The water table is
imaged as a prominent horizontal reflection that cuts across
dune strata at Penney Hill (Figure 5a,b) and follows the predune surface at Snow Hill (Figure 6a,b).
A sediment sample taken from dune foresets on the upwind
side of Penney Hill (Figure 5c) gives a PSL burial date of 143
6 16 years (PEH97-1, Table 3). This corresponds to about
1855 AD. Although the dune strata sampled are nearly the
oldest preserved strata within the dune, this date represents
a minimum age of dune development because older dune
strata may have been entirely eroded during dune migration.
Run Hill
Figure 2. a. Aerial photo of Run Hill dune prior to significant urban
development. It is migrating over parabolic dune ridges of the northern
edge of Nags Head Woods dune field, which is stabilized and covered with
mature maritime forest. Dashed line indicates position of precipitation
ridge (leading dune) of Nags Head Woods dune field where it continues
under Run Hill. (Original scale 1:28,000, March 6, 1952, Frame 179,
source unknown) b. Aerial photo-mosaic of Jockeys Ridge dunes. Numbers
1–4 are crests of the 4 dunes that comprise this dune mass. Profiles in
Figure 4b were measured along line labeled S. (Photos taken Nov. 6, 1995
at 10 5 8009 by N.C. Department of Transportation.)
The internal stratigraphy of Run Hill is more complex (Figure 7). A prominent sub-horizontal reflection at a depth of
270 ns (18 m) on transect RH1r1 (Figure 7a) was determined
by auger to be the water table. A prominent hummocky reflection with up to 20 m relief, identified in outcrop as a buried soil (PS2), separates two major packages of high-angle
reflections (DP1, DP3, Figure 7a,b). The buried soil, a Typic
Quartzipsamment, is thin and is characterized by a dark gray
A horizon that is weakly cemented by humus, forming small
(10 cm) scarps where exposed at the surface. A subsoil (B)
horizon of variable thickness is weakly stained by iron and a
thin leached (E) horizon may be present (Table 4a, Figure
8a). The widespread extent of the buried soil and its characteristic level of development suggest it formed under a well
developed forest that generated a continuous litter layer for
a period of many decades to a few hundred years. By comparison, soils on coastal dunes in the mid-Atlantic states that
form over a longer time period (a few thousand years) develop
into Spodic Quartzipsamments. These soils develop irregular
dark brown patches and pendants in their B horizons where
iron, aluminum and organic coatings accumulate (HATCH et
al., 1985; WHITTECAR et al., 1982; Whittecar and Baker,
1984). Tree stumps rooted in the buried soil (e.g., Figure 8a)
have radiocarbon ages corresponding to calendric dates of ca.
1650 AD or younger (samples from 4 sites, Table 2, Figure
7c).
Journal of Coastal Research, Vol. 20, No. 4, 2004
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Figure 3. Maps of the vicinity of Run Hill and Jockeys Ridge. 1851 map, Kill Devil Hills to Nags Head, N.C., U.S. Coast Survey, Register #351, original
at 1:20,000 courtesy of Outer Banks History Center. Modern 7.59 U.S.G.S. topographic maps, originals at 1:24,000, portions of Manteo (1953) and Kitty
Hawk (1982) sheets spliced at 368N latitude.
Reflections in the unit below the buried soil (DP1) dip
steeply to the SE (up to 168) and SW (up to 298) and are
interpreted to be strata formed by dunes during an earlier
phase of activity. Thickness of the lower unit is variable. A
mound in this unit that rises to 13 m above the water table
(PR in Figure 7b), corresponds in shape and location to the
ridge on the western (leading) edge of the Nags Head Woods
dune field to the south that is being buried by Run Hill. This
precipitation ridge (leading dune migrating over vegetated
coastal area, COOPER, 1958; also termed long-walled transgressive ridge, THOM, 1978) of the older dune complex extends southward along the edge of the field of stabilized, tree-
Journal of Coastal Research, Vol. 20, No. 4, 2004
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987
Figure 4. a. Time series of land use maps of eastern Run Hill, originally drawn from aerial photographs scaled at 1:6000. 1952 photo shown in Figure
2a. 1970 photo: taken Nov. 24 at 1:12,000, Frame 98, source unknown. 1982 photo: taken Nov. 30 at 1:6000, frame 3-63, by Kimball and Assoc. for Dare
Co. 1996 photo: taken April 3 at 1:6000, frame 36-17 by Kimball and Assoc. for Dare Co. b. Successive profiles of the leading edge of the southernmost
dune of the Jockeys Ridge group (position S, dune 4, Figure 2b) beginning in Jan. 1995 when 15,000 cubic yards (11,500 m3) of sand were removed to
protect the road.
covered parabolic dunes (Figure 2a). GPR shows three bundles of predominantly SW dipping reflections separated by
northeast dipping reflections within this ridge. The geometry
indicates that the ridge grew by successive dunes stacking up
to form the high precipitation ridge (Figure 7b, position 40NE
to 70SW). A very limited number of trench exposures of the
dune strata of unit DP1 reveal a wide variety of dune foreset
orientations (true dip azimuths of N628W, N258E, S118W,
S648E), and foreset dip angles ranging from near-horizontal
to 358. Disruptions of low-angle strata suggest the presence
of vegetation during deposition. Overall, the characteristics
of the strata in the lower sediment package (DP1) are consistent with formation by parabolic dunes. Sediment from
this unit gives a PSL date of deposition of about 765 AD (1232
6 65 yrs, RNH97-1, Table 3, Figure 7c).
The upper unit (DP3) comprises two sub-units. The main
subunit (a) is composed of steeply dipping reflections that dip
predominantly to the southern quadrant, and represent dune
foresets generated by migration of the main dune bedform
(Figure 7a). These were observed in several places in surface
exposures and trenches. The less extensive subunit (b), located atop subunit a, has reflections dipping generally eastward. These are confirmed by trench exposures to be strata
formed by the eastward migration of superimposed dunes on
Run Hill (S898E, WEAVER et al., 1997), and are inferred to be
separated from the main dune strata by a bounding surface
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Figure 5. Penney Hill dune. a,b. Representative GPR transects showing interpretation on lower transect. GPR reveals Penney Hill to be a relatively
simple dune with no buried soils. Reflection identified as water table confirmed by auger, pre-dune surface confirmed by auger and natural exposure at
south end of dune. Dune foreset strata confirmed by trenches. c. Outline map of Penney Hill barchan showing locations of GPR transects, trenches and
auger holes, and sample site for dune age determination.
(e.g., Figure 7a, position 250–310). A sample taken from dune
foresets in unit DP3 above the buried soil has a PSL deposition age of about 1890 AD (108 6 11 yrs; RNH97-5, Table
3, Figure 7c).
Jockeys Ridge
Jockeys Ridge stratigraphy displays even greater complexity (Figures 9–11). One major extensive reflection can be
traced throughout much of the sampled area at depths of up
to about 300 ns (25 m) below the surface (PS2, Figures 10,
11). The undulatory (up to 15 m relief) reflection approaches
the dune surface in several locations where it can be identified in outcrop as a buried soil atop an irregular dune surface
(Figure 8b). The upper buried soil (PS2) at Jockeys Ridge is
very similar to the buried soil at Run Hill (Table 4a–c). A
greater range of properties (horizon thickness, color) is seen
at Jockeys Ridge because buried soil profiles now exposed
formed in a wider range of landscape positions and drainage
conditions (swales and toeslopes predominate) than the bur-
ied soil exposures seen at Run Hill (mostly well drained crest
and upper slope sites). Darker color in the A horizons reflects
abundant charcoal, which is absent at Run Hill (WHITTECAR
et al., 1998). A stump, wood fragments and soil organics from
buried soil PS2 provide radiocarbon ages of 1650 AD or later
(Table 2, Figure 9).
A second prominent undulatory reflection is present in
some areas below the upper (PS2) reflection (Figures 10, 11).
This reflection has 10 m of relief and where it is exposed at
the surface it is identified as a well developed buried soil
(PS1), twice as thick as the upper buried soil. Soil morphology
is also more complex with multiple dark A and pale gray E
horizons and dark brown soil lamellae up to 3 mm thick (Table 4d; Figure 8c). Where well preserved and exposed, the
lower soil profile has a notable pale yellow ‘‘color B’’ horizon.
Although the thicknesses and strength of colors in the E and
B horizons vary among outcrops, they are within ranges typical of soils on young Holocene dunes. Carbonized wood fragments from buried soil PS1 provide radiocarbon ages corre-
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989
Figure 6. Snow Hill dune. a,b. Representative GPR transects. GPR reveals Snow Hill to be a relatively simple dune with no buried soils. Reflections
identified as water table and pre-dune surface confirmed by auger, dune foreset strata confirmed by trenches. True dip angle and azimuth shown at
transect intersection is from stereonet manipulation. The sloping water table surface in transect FC1c2 is anomalous and may result from an error in
topographic measurement west of position 105. We were unable to return to the site to confirm this. c. Outline map; note that Snow Hill is beginning to
develop the shape of a parabolic dune with trailing arms. Locations of GPR transects, trench and auger hole shown.
sponding to calendric dates of 885–1285 AD and 1260–1410
AD; soil organics date to 980–1025 AD (Table 2).
Jockeys Ridge dune strata are divided into three packages
by the two buried soils, each with an irregular geometry. The
upper package (DP3), above the upper buried soil, is up to 20
m thick and is the most clearly and extensively imaged. On
east-west transects reflections dip predominantly westward
(e.g., Figure 10b); on north-south transects reflections dip predominantly southward (e.g., Figure 10d,e). Trenches confirm
that these reflections represent dune foreset strata with true
dips predominantly towards the southwestern quadrant, representing migration of dune lee slopes in this direction in
response to the prevailing wind. Wind reversals are recorded
primarily in multiple bounding surfaces (reactivation surfaces) that truncate dune strata (e.g., Figure 11c). Sediment from
dune foresets in unit DP3 give a PSL age of about 1810 AD
(187 6 15 yrs BP, JRDG95-1, Table 3).
The package of reflections between the two buried soils
(unit DP2) is up to 15 m thick and is clearly imaged in a few
areas. Reflections dip predominantly westward on east-west
transects (e.g., Figure 10c, 11b) although eastward-dipping
reflections are also present (e.g., Figure 10b). Exposures of
these strata confirm that they are also dune foreset strata.
Sediment from the middle sediment package (DP2) gives a
PSL deposition age of about 1260 AD (742 6 51 yrs BP, JKR
97-1, Table 3).
Below the lower buried soil is a third package of reflections
(unit DP1), which, where imaged on a north-south transect,
displays reflections that dip steeply to the south (Figure 11a).
On east-west transects reflections dip both to the west and
to the east (Figure 10b). A trench confirms that these are
dune foreset strata. The base of unit DP3 is shallow and reflective enough to be imaged on some transects and is interpreted to be the pre-dune surface (e.g., Figure 11a). In some
areas it is imaged as an extremely prominent double reflection (Figures 10b–d), and is tentatively interpreted as a
shelly gravel lag by comparison with related GPR work elsewhere on the North Carolina coastal plain. Locally, packages
Journal of Coastal Research, Vol. 20, No. 4, 2004
Figure 7. Run Hill dune. a,b. Representative GPR transects. Run Hill displays an older dune package (DP1) below a buried soil (PS2), and an upper dune package comprised of two parts. The
main dune foresets dip to the SW (DP3a) and, above a bounding surface, superimposed dune foresets dip to the E (DP3b). c. Outline map of Run Hill, showing locations of GPR transects, sites
where these were ground-truthed, and sample sites for dune and buried soil age determination.
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Figure 8. Photos of buried soils. a. Buried soil profile (PS2) on Run Hill (see Table 4a for description). Weakly developed A, E, and B horizons noted.
In situ carbonized tree trunk (arrow) buried by dune after soil development; this is the source of the wood for radiocarbon samples RH97-1,2 (Figure 7c,
Table 2). The stump appears lower than the soil because the soil slopes very steeply towards the viewer. b. Concave-up exposure of upper buried soil
(PS2) formed in interdune swale on Jockeys Ridge. Numerous exposures of such soil-capped swales are visible in the northern half of the dune after
periods of strong deflation. Shovel handle (arrow) is approximately 10 cm long. c. Distinctive features in the upper horizons of the lower buried soil (PS1)
at Jockeys Ridge (see Table 4d for description, location). Note the relatively thick soil lamellae formed in the A and E horizons and the multiple humusrich (cumulic?) zones within the A horizon.
of sub-horizontal to dipping reflections are imaged below the
pre-dune surface, suggesting the nature of barrier island
stratigraphy (Figures 10a,c,d, 11a). A dominant sub-horizontal reflection imaged only in the finer-scale GPR transects
(Figure 11) was identified by augering as the water table.
Additional Dates from Nags Head Woods Dunes
PSL dates have been determined in two places on highangle dune foreset strata of stabilized parabolic dunes in the
Nags Head Woods dune field (Table 3). These sediments, deposited in the southern half of the dune field, between Run
Hill and Jockeys Ridge, give PSL depositional dates of about
960 AD (1037 6 60 yrs, NHW95-12) and about 1175 AD (826
6 69 yrs, NHW95-4).
PHASES OF DUNE ACTIVITY AND STABILITY
Three phases of dune activity punctuated by two phases of
dune stability are recognized in the stratigraphy of the active
dunes in this study (Figure 12). Strata from the earliest dune
phase (DP1) are preserved at Run Hill and Jockeys Ridge,
and in the stabilized dunes of Nags Head Woods. Dune activ-
ity dates to about 765 AD at Run Hill and 960 AD in the
southern part of Nags Head Woods (PSL method). Jockeys
Ridge experienced stabilization and soil formation (PS1) by
1000 AD (radiocarbon method). Based on degree of development, the soil formed on the dune surface over a period of
several hundred years. A corresponding soil is not found on
Run Hill. Either Run Hill remained active and eolian sediments deposited during this time were not preserved or not
sampled for luminescence dating, or the first buried soil (PS1)
developed as at Jockeys Ridge, but was entirely removed during an ensuing phase of eolian activity. Additionally, at least
one dune ridge in Nags Head Woods dune field was active at
1175 AD (PSL method), indicating that while a soil developed
in the Jockeys Ridge area, partially vegetated parabolic
dunes remained active nearby to the north.
A second phase of dune activity (DP2) resumed by 1260 AD
at Jockeys Ridge (PSL method), partially burying and partially deflating the older soil. Sediment of this depositional
age was not found on the other dunes. A second phase of
stabilization occurred by 1700 AD (radiocarbon method). Soil
formed during this time is represented at both Run Hill and
Jockeys Ridge (PS2). Being less well developed than buried
Journal of Coastal Research, Vol. 20, No. 4, 2004
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soil PS1, it likely formed over a somewhat shorter time period. By 1810 AD (PSL method) the modern active dunes of
dune phase 3 (DP3) were burying this younger soil at Jockeys
Ridge. Samples from strata of this phase of activity from Penney Hill and Run Hill date to ca. 1855 and 1890, respectively.
Although not dated, it is assumed that Snow Hill, with no
buried soils, also formed during this latest phase of dune activity.
On all four study dunes, dune strata formed during dune
phase 3 are composed primarily of steep lee-slope strata that
dip in a southerly to southwesterly direction, and can be inferred to have formed as a result of typical transverse dune
migration. Evidence of wind reversals is primarily preserved
in reactivation surfaces formed by erosion of the upper lee
slope. These surfaces are subsequently buried as prevailing
winds resume and the southwest-facing slipface rebuilds and
continues to migrate. The reactivation surfaces were imaged
with GPR on all 4 dunes, but are best displayed at Jockeys
Ridge (Figure 11c). Similar strata are sketched by HUNTER
(1981, Figure 10c) and have been documented, for example,
at White Sands where they were formed by simple transverse
crescentic dunes in a bimodal wind regime (CRABAUGH,
1994).
CAUSES OF DUNE DEVELOPMENT AND
STABILIZATION
Back-barrier dunes develop where there is an adequate
supply of sand available to wind strong enough to move the
sand (e.g., KOCUREK and LANCASTER, 1999). In humid coastal regions, vegetation is an important control on sediment
availability (HESP and THOM, 1990). For dunes to migrate
into the vegetated back-barrier area, the combination of sediment supply and wind velocity must be sufficient to overcome the tendency of vegetation to stabilize the wind-blown
sand. A number of causes of humid coastal back-barrier dune
initiation have been described (e.g., PYE, 1983; HESP and
THOM, 1990; KLIJN, 1990). Some initiate localized dune development, such as fire or sediment supplied at a stream
mouth. Others potentially affect much a broader region, such
as sea level changes or climatic shifts. Causes of dune development and stabilization in the study area are discussed below, based on the stratigraphy and resulting chronology of
dune activity and stabilization (Figure 12).
Sediment Supply
The Atlantic coast in the study area comprises a relatively
straight, continuous barrier spit with only one active inlet
(Figure 1d). The only potential modern sources of sand are
river sediments from Chesapeake Bay to the north, and erosion of sediment from the inner shelf or sedimentary units
that occur in the barrier shoreface. The greatest amount of
dune development over time is concentrated in the Jockeys
Ridge/Run Hill/Nags Head Woods area. All three dune phases
are represented here, as are the largest modern dunes. Highresolution seismic and vibracore studies have shown that the
Run Hill/Nags Head Woods/Jockeys Ridge dune mass is located where the Roanoke paleochannel traverses the modern
coast (Figure 1c; RIGGS et al., 1992). This fluvial channel,
incised into the shelf during the last sea level lowstand, filled
with fluvial and estuarine sediments. These sediments are
the largest potential source of unconsolidated quartz sand between Cape Hatteras and Cape Henry (RIGGS et al., 1995).
The sand would have become available at the Atlantic coast
as the shoreface ravinement surface progressively eroded the
inner shelf during the Holocene sea level rise (RIGGS et al.,
1992).
Sediment sources for the smaller modern dunes in the
study area north of Run Hill (such as Snow and Penney Hills,
Figure 1d) are more difficult to identify. Sediment could have
been made available by closing of former inlets. Snow Hill is
located south of an unnamed prehistoric inlet and Penney
Hill rests at the southern edge of the relict tidal delta of the
New Currituck Inlet (Figure 1d). Another potential source of
sand is washover events (ROSEN, 1979; LEATHERMAN, 1976;
KOCHEL and WAMPFLER, 1989).
Forcing Factors
Coastal back-barrier dunes have formed in a number of
humid coastal areas in the last millennium, particularly in
the last 400 years. Formation of these dunefields has been
attributed to a variety of factors including fire damage (e.g.,
FILION, 1984), overgrazing (e.g., MCCANN and BYRNE, 1994),
coastal progradation (e.g., CHRISTIANSEN and BOWMAN,
1986), sea-level (or lake-level) rise (e.g., LOOPE and ARBOGAST, 2000), climate deterioration during the Little Ice Age
(GROVE, 1988) from the 1200’s to 1850 AD (e.g., PYE and
NEAL, 1993) and combinations of these (e.g., CLEMMENSEN et
al., 1996; JELGERSMA and VAN REGTEREN, 1969). For the
study area the first three of these factors can be ruled out as
causes for development of modern dunes (DP3). The buried
soil at Run Hill (PS2) that underlies the modern dune shows
no evidence of fire; vegetation studies suggest that overgrazing has not had significant impact in the area (F ROST, 1999);
absence of natural foredunes or modern beach ridge plains
indicates this shoreline was likely erosional during formation
of modern dunes. Climatic deterioration (increased storminess, cooler temperatures) associated with the later stages of
the Little Ice Age, and rising sea level since 1600 AD (SAGER
and RIGGS, 1998) are more likely contributing causes of modern dune development in the study area. Combined with
drought conditions that persisted in this region from about
1650 to the late 1800’s (STAHLE et al., 1988), cooler temperatures, increased storminess and gradually rising sea level
could have provided the right combination of conditions for
dune activation. Rising sea level and more severe wave climate probably increased coastal erosion, opening inlets and
increasing overwash, moving more sediment onto land. Increased wind velocities and decreased vegetation in drought
conditions likely enhanced eolian transport and dune sand
movement.
It may be possible to attribute timing of the two earlier
dune phases and the ensuing periods of dune stabilization to
climatic variation, as well. The middle dune phase at Jockeys
Ridge (DP2 at ca. 1260 AD) occurred near the beginning of
the climatic deterioration leading to the Little Ice Age (PORTER, 1986). It also occurred near the end of nearly a century
Journal of Coastal Research, Vol. 20, No. 4, 2004
Coastal Dune Stratigraphy
Figure 9. Map of Jockeys Ridge showing locations of GPR transects and
sample sites for dune and buried soil age determination. Area of map
shown on Figure 2b.
of persistent drought in this region that accompanied the Medieval Climatic Anomaly (STAHLE et al., 1988). Although the
M.C.A. was a period of more temperate climate in Europe (ca.
1000–1300 AD, LAMB, 1985; GROVE, 1988) and few documented glacial advances in the northern hemisphere (1090–
1230 AD, PORTER, 1986), it brought aridity in the southwestern U.S. (ca. 900–1350 AD, STINE, 1994) and to the midAtlantic coast (;1050–1280 AD, STAHLE et al., 1988). The
younger soil (PS1) formed sometime after 1300 AD and before
the modern dune activity. The 14th through 16th centuries
was a relatively wet period in this area (STAHLE et al., 1988).
The older, more well-developed soil (PS1) at Jockeys Ridge
developed by around 1000 AD. The century from about 950
to 1050 AD was on average a rather wet period in this region
(STAHLE et al., 1988). The older phase of dune formation
(DP1, ca. 765 AD) occurred at about the time of the most
severe drought indicated in the 1600-year tree-ring climate
proxy record for the region, and near the end of a century
993
dominated on average by drier conditions (STAHLE et al.,
1988). This time also corresponds to the period of early Medieval glacial advances, which may have had a climate more
similar to the Little Ice Age (PORTER, 1986).
External forcing factors, such as a climate change, are
likely not necessary to explain every event of dune stabilization in a humid coastal region. As dunes migrate inland
they move away from their sediment source near the shore,
where surf and salt spray limit vegetation growth, and into
an ecological zone where vegetation can begin to take hold
on the dune. A typical sequence for a coastal transverse
dune is to be progressively vegetated, turning into an active
parabolic dune, and finally becoming fully stabilized, a process that has been documented in aerial photographs for the
False Cape dunes in Virginia (HENNIGAR, 1977) and the
south coast of Israel (TSOAR and BLUMBERG, 2002), and in
topographic maps for the Rabjerg Mile in Denmark (ANTHONSEN et al., 1996). Such partly or fully stabilized parabolic forms are common on humid coasts around the world
(e.g., Australia, Europe and NW U.S.A, review in PYE and
TSOAR, 1990, p. 200; also New Zealand, BROTHERS, 1954;
South Africa, TINLEY, 1985; Sri Lanka, SWAN, 1979). Because the past hundred years was a period of warming and
moist conditions, it is difficult to determine whether such
twentieth-century coastal dune stabilization by vegetation
is driven primarily by climatic effects, or whether it is the
natural sequence of events for such dunes in any climatic
conditions. Various human impacts on the dunes also complicate the interpretation. However, the overall results of
this study suggest that climate contributes to phases of development and stabilization of coastal dunes on humid
coasts. Dune formation is associated with drought periods
and dune stabilization and soil formation is associated with
moister conditions. Increased storminess and may also contribute to dune activation.
CONCLUSIONS
1. Of four active modern dunes studied along the Atlantic
coast of northeastern North Carolina and southeastern Virginia, the two smaller, more northern dunes show only one
phase of eolian activity. The two larger, more southern dunes
record more than one phase of dune development, punctuated
by periods of stabilization with vegetation and soil development.
2. The sequence of phases of dune activity and stabilization of these four dunes is as follows, listed youngest to oldest
to parallel Figure 12.
Dune Phase 3
Buried Soil 2
Dune Phase 2
Buried Soil 1
Dune Phase 1
All dunes
Run Hill
Jockeys Ridge
Jockeys Ridge
(Run Hill?)
Jockeys Ridge
(Run Hill?)
Run Hill
Jockeys Ridge
active since at least 1810 AD
developed by 1700 AD
active by 1260 AD
developed by 1000 AD
active by 765 AD
The Nags Head Woods dune field, active by 765 AD at Run
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994
Havholm et al.
Figure 10. Representative GPR transects of Jockeys Ridge dunes imaged with GSSI equipment (Table 1). See Figure 9 for transect locations. a–c
Transects with west-east orientation. d,e Transects with north-south orientation.
Hill, remained active in areas between Jockeys Ridge and
Run Hill through at least 1175 AD. This suggests that the
stabilizing conditions under which the first soil (PS1) developed at Jockeys Ridge were represented, in the southern
Nags Head Woods dunes, by development of parabolic dunes
that remained active.
3. The larger, longer-lived dune systems formed only in the
vicinity of Run Hill and Jockeys Ridge, which suggests a localized source of sediment for the large volume of eolian sand.
The paleochannel of the Roanoke River, the major trunk
stream draining this portion of the coastal plain/piedmont
during glacial times, passes under the barrier island in the
vicinity of these dunes. The fluvial and estuarine sediment
fill of this channel likely provided the source of abundant
sand-size sediment for later reworking by littoral and finally
eolian processes.
4. The temporal distribution of dune and soil development
in the study area suggests that dune activation and stabilization may be related to climatic fluctuations. All three phases of dune development are associated with extended and/or
severe drought conditions. Soils develop during periods of extended humid conditions.
5. Widespread development of back-barrier dunes at intervals along the Atlantic coast in the study area since 1700 AD
is tentatively attributed to a combination of drought, increased storminess associated with the Little Ice Age, and a
gradual sea level rise. Increased storm frequency and rising
sea level probably caused increased erosion and transfer of
sediment from the foreshore to the coast; increased wind and
decreased vegetation allowed that sand to be efficiently reworked by the wind. Storm overwash and ebb tidal delta
sands associated with closed inlets may have provided the
primary point sources of unvegetated sediment available for
development into eolian dunes.
Journal of Coastal Research, Vol. 20, No. 4, 2004
Coastal Dune Stratigraphy
995
Figure 10. Continued.
ACKNOWLEDGMENTS
We greatly appreciate logistical and financial assistance
from the following: Nags Head Woods Ecological Preserve
and The Nature Conservancy (Barb Blonder and Jeff Smith
DeBlieu), Jockeys Ridge State Park (George Barnes and Kelley Thompson), Friends of Jockeys Ridge State Park (Peggy
Birkemeier), North Carolina Department of Parks and Recreation (Marshall Ellis and Sue Regier), and the Field Re-
search Facility of the Army Corps of Engineers at Duck (Bill
Birkemeier). This project was also supported financially by
the Office of University Research and Sponsored Projects at
the University of Wisconsin-Eau Claire and East Carolina
University Geology Department. False Cape State Park provided access to Snow Hill. Invaluable assistance in the field
was provided by Dan Holloway, Sarah Weaver, Jan DeBlieu,
Chad Bartz, Ann and Dick Wood, Con Weltman, and Stacin
Martin.
Journal of Coastal Research, Vol. 20, No. 4, 2004
Figure 11. Representative finer-scale ground penetrating radar transects of the northern end of Jockeys Ridge, imaged with pulseEKKO equipment (Table 1). See Figure 9 for transect locations.
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Journal of Coastal Research, Vol. 20, No. 4, 2004
Coastal Dune Stratigraphy
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Figure 12. Schematic depiction of phases of dune development, stabilization, and soil development of Run Hill and Jockeys Ridge. Snow Hill and Penney
Hill, not shown, have no buried soils and have likely been active only during Dune Phase 3.
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