On the Origin of Parabolic Dunes
Near Friar's Head, Long Island, New York
Steven C. Englebright1, Gilbert N. Hanson2, Troy
Rasbury3, and Eric E. Lamont4
1Curator of Geology, Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794
2Professor of Geology, Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794
3Assistant Professor of Geology, Department of Geosciences, State University of New York, Stony Brook, NY 11794
4Research Associate, New York Botanical Garden, Bronx, New York 10458
This web page (slightly modified by G.N. Hanson) is from a publication in the Long Island
Botanical Society Quarterly Newsletter, vol. 10, no. 1, Jan-Mar, 2000 LIBS@nativeamerica.com
A pdf file of this publication is available for printing. Link here to pdf file On the Origin of
Parabolic Dunes New Friar's Head, Long Island, New York. Be patient while it downloads
it is an 7,700 KB file.
Color photos of the Grandifolia
Sand Hills by Steven C. Englebright can be found at this link.
Some of the images below are thumbnails. Click on the
image for a larger image.
An analysis of the Grandifolia Sandhills
(Long Island, New York) reveals that a series
of dune forms and an associated endemic forest dominated by American Beech
(Fagus grandifolia) located on and adjacent to Long Island Sound
bluffs exceeding 100 feet in height are probable
Late Pleistocene climatic relics. Information
derived from both historic U.S. Coast and Geodetic
Survey charts and U.S. Geological Survey digital
elevation maps demonstrates that the Sandhills are parabolic dunes that have been truncated by
long term erosional recession of the Long Island
Dwarf American Beech (Fagus grandifolia) as found at
Baiting Hollow, Long Island
Extrapolation of original dunefield
structure indicates that many individual dunes spanned a
dunefield that was at least one mile in width and that all originated from a northwesterly sand
source that appears to have been drowned by the
post-glacial eustatic rise of sea level. Shore face
retreat has removed more than half of the initial length
of many surviving Grandifolia dunes, a process
that could only have occurred over thousands of years.
Large parabolic dunes similar to these occur
in contemporary periglacial regions. The
Grandifolia Sandhills apparently began to form
approximately 18,000 years before present when the
last periglacial climate affected coastal New York
Many of these dunes ascended the east-west
trending spine of the Harbor Hill Moraine (Fuller,
1914) and were stranded in their present position
when winds powerful and persistent enough to move them dissipated as the climate ameliorated.
Although tundra vegetation probably helped
trap and bind loose sand to create these parabolic dunes, when the
climate warmed enough to support trees Fagus
grandifolia--possibly in a dwarf form living at
the edge of the range of the species--may have
been the earliest tree to colonize. Once
established, this species gradually modified surficial dune
sand into a soil that promoted its domination and
As shore face retreat undercut dune and
forest over thousands of years the parent Fagus
grandifolia population tenaciously
evolved--or reverted to-- a unique dwarf morph that may
have been the pioneer.
Although dwarfism today occurs on
these dunes other than where the forest is undercut,
the pygmy form appears to grow in particularly stressed micro-environments that are distal
from water or where soil may be thin such as dune crests. Dwarf trees are most abundant
where the fabric of the forest runs down the steep
Sound shore bluff to be continually cut back by
slumping and other effects of storm waves. This biogeologic phenomenon appears to be
globally singular. Preservation for scientific
research, study, and education is recommended.
Previous reports on the possible
geological origins of a series of sandy hills overlooking
Long Island Sound near Friar's Head, Riverhead,
New York have not provided interpretations that
simultaneously explain both these hills and the
apparently unique presence of a forest dominated
by dwarf and other growth forms of the American beech
Most workers, including Lewis (1876),
Fuller (1914), and Black (1998), have concluded
that these features are dunes.
Recent analysis by Terchunian and
Sirkin (1999) suggest that the Grandifolia Sandhills
have glacio-fluvial cores that are merely veneered
by locally derived wind-blown sediment which became mobile as a result of mid-19th century
land clearing activities. This explanation does not
reconcile with clearly observable geomorphic
and bio-geological phenomena.
USGS map circa 1838
The large dune called Friar's Head was so named
when sailors saw a similarity to an elevated, exposed dune area encircled by dwarf Beech Trees.
USGS map circa 1885
Note that on each of these historic maps mature trees were recorded
for the dune area.
An alternate interpretation, not
previously reported, is that these features are the result
of aeolian processes in a periglacial climate and that the population of
Fagus grandifolia found here has for thousands of years trapped,
bound, adapted to, and modified the sediment and
soil chemistry of ancient parabolic duneforms (see addendum). Vegetationally detailed
maps produced by the USCGS in, respectively, 1838 and 1885 demonstrate that the
Grandifolia Sandhills remained largely vegetated during
the mid-19th century.
The idea that the Grandifolia Sandhills is
no more than a thin veneer of sand resulting from wood harvesting activities south of the
eroding bluffs during the time interval of the last
hundred or so years (Terchunian and Sirken, 1999) is
not supported by any evidence. Historic maps show cultivated fields adjacent to
sand hills that
appear to have been continuously vegetated. With
the exception of laborious clearings for farm
fields, the wood cutting activities of the nineteenth
century typically did not injure or remove tree
roots. Without root removal vigorous re-growth, not
soil erosion or abundant loose sand, would have
been the expected result of wood cutting. This
conforms with the observations of Good and Good
(1970) who concluded that "None of it (the
Grandifolia Sandhills) was ever farmed, although timber
was cut to supply firewood for New York City in
the late 1800's".
Aerial Photograph of the Grandifolia Sandhills. The feature in the lower left corner, the DeFriest Blowout,
is the largest dune blowout on Long Island's north shore.
The oblique "shadow effect" on a colored
Digital Elevation Map (DEM) based upon a U.S. Geological Survey
71/2o quadrangle shows numerous northwest-southeast trending parabolic dunes
both east and west of Friar's Head. Because the
curvilinear shapes of these structures also define
the boundaries of the Grandifolia Sandhills, it
appears that these relief features of aeolian origin.
The DEM clearly shows that this field of dunes is
truncated by the erosional scarp that characterizes
the eastern half of Long Island's north shore.
This truncation not only demonstrates the
pre-modern origin of the Grandifolia Sandhills, but
suggests that the north fork of Long Island was a
once much more extensive land surface across which these dunes migrated.
1999 USGS digital elevation map (DEM) based upon a 71/2'
quadrangle topo map. The computer generated
shadow effect simulates an early morning (eastern) sun.
1999 USGS DEM with preliminary dune
reconstruction extrapolated into the basin of the Long Island Sound.
The extent to which dunes are eroded indicates the minimal
extent of postglacial shoreface retreat for this coast.
The slip faces of upwards of ten large
parabolic dunes are preserved where they collided with
the north side of the Harbor Hill Moraine and each other. It appears that many climbed to its
height before stranding occurred. Before
encountering the moraine most of these dunes were
apparently thirty to more than fifty feet high. Ground
penetrating radar, coring, examination of primary
bedding structures, detailed mineralogic analysis,
and other research should determine the full extent
to which the Grandifolia dunes are comparable to modern cold climate parabolic dunes of the
Retreat of the Late Wisconsinan glacier
from southern New England is believed to have
occurred between 20,000 to 15,000 years before present.
This occurence inevitably caused a dramatic climate change; the region's previous wind
and weather patterns adjusted. As the climate
warmed, the dunes were trapped and bound by the
subsequent colonization of Fagus
The prevailing wind that created these
dunes came from the northwest and must have been
both powerful and persistent. While the prevailing
wind during Long Island's stormy winter season is
today from the northwest, typical modern storms are relatively weak and have not created dunes
like these anywhere along the Long Island
Sound shore. Modern hurricanes, while potentially
powerful enough to create parabolic dunes forms on Long Island, typically track from the south
and are of limited frequency and duration. The Grandifolia Sandhills are, therefore, relics of
a dramatically different glacial fringe regional
climate. Within this context, the Grandifolia Sandhills exist despite, rather than because
of, modern wind patterns.
Close up of dune sand from the Grandifolia
Sandhills. Note the high degree of sorting. Preliminary
examination of this sand including its narrow range of grain
sizes and shapes, color, mineralogic composition, and
other characteristics suggests that it may be a secondary deposit of Cretaceous sand. Based upon dune orientation it
is inferred that the primary Cretaceous deposit or
source was in the north-central portion of what is now the
Long Island Sound when sea level was lower and portions of this basin were
Glaciofluvial deposits typical of the study area.
Exposure is in an excavation immediately south of
the Harbor Hill moraine near the DeFriest Blowout. Note the wide range of particle sizes.
Large re-exposed glacial erratics in the DeFreist
Blowout. These rocks are part of the morainal
landscape that was buried by parabolic dunes active in
the periglacial climate that followed deglaciation.
Dunes that are similar to the
Grandifolia Sandhills in size, shape, relief, and orientation
are found at Hither Hills State Park near the
eastern edge of Napeague Bay in East Hampton Town
on Long Island's south fork. As with the
Grandifolia Sandhills, no modern source of sediment has
been convincingly identified for the Napeague
Dunes. Expansive growth of Fagus
grandifolia is not evident at the Napeague Dunes where an
oak-pine forest performs a similar function. While this
and other vegetational differences distinguish
these two dune fields, the comparable size and shape
of the dunes, their northwest-southeast
orientation and other geomorphic similarities are striking.
Further investigation is needed to determine whether the Napeague Dunes are of mixed
ages or if they may all have been created when sea
level was low and a common tundra landscape connected what is now the North and South Forks
of eastern Long Island to sand sources in the Long Island Sound Basin.
The relic vegetation and parabolic dunes at
and near Friar's Head are unique. They appear to
be among the rarest of landforms still extant from
a now vanished climate and time when Long Island's landscape was both exceedingly cold
and vegetationally primitive. The globally
singular association of Fagus grandifolia with this
ancient climatic relic duneform offers an exceptional
opportunity for scientific research and study.
Preservation of the Grandifolia Sandhills would be consistent with the wise decision previously
made that created preservation of the Napeague Dunes.
Such preservation would provide opportunity for the public to appreciate and enjoy an
important and remarkable part of their natural history heritage. Link
here for a proposed sequence of events for the development of the
Grandifolia Sand Hills during the late Wisconsin to the present.
Eastern Long Island showing the location of all known parabolic dunes in coastal New York. Note that these dunes, found
only at Riverhead and East Hampton, are similarly oriented. The Riverhead dunes appear to have been climbing the north side of
the Harbor Hill Moraine when a changing climate stranded them. Still undetermined is whether the dunes at Napeague also
originated from a now submerged sediment source in the Long Island Sound Basin.If so, they could have advanced to their
present position after moving through one of the gaps in the easternmost Harbor Hill Moraine.The subsequent rise of sea level
has flooded both the Long Island Sound and Peconic Bay estuaries. On each fork it has also constructed connecting beaches
across morainal gaps to form tombolo complexes. On the South Fork, rising sea level has elevated the
water table, created extensive freshwater wetlands, and apparently begun to drown the Napeague Dunes.
Area of Baiting Hollow, Town of Riverhead, showing
large parabolic dunes that have been significantly truncated by erosion associated with long term shoreface retreat.
Area of Napeague, East Hampton, showing
parabolic dune forms similar in size and orientation to those of
the Grandifolia Sandhills. Unlike the dunes near Baiting
Hollow these appear to have been preserved with most of their
Historical Accounts of the Grandifolia Sandhills
1876 Elias Lewis, Jr. (Geologist)
"At this point is the great dune known on the Coast Survey charts (1838) as Friar's Head. The sand blown from this spot and from the flanks of the dune constitute the semicircular
wall....Published in "The Popular Science Monthly", January Issue
1914 Myron L Fuller (Geologist, Department of the Interior)
"In fact, it is not unlikely that considerable areas of the ridges mapped as moraines are only
pseudomoraines composed of dune sand, although they may contain a core of morainal drift."
--"The Geology of Long Island", US Geological Survey, Professional Paper 82
1938 Roy Latham (Long Island's premier naturalist)
"...very high sand dunes there and fine heavy woods. Polypodium vulgare Fern: the most of the
species I ever saw - beds 40 by 100 feet thickly green with
it." --March 9th entry in his Journal
1970 Ralph E. Good and Norma F. Good (Department of Biology, Rutgers University, New Jersey)
"All of the vegetation studied is developed on dune sand deposits which form sea cliffs and
uplands."--"Bulletin of the Torrey Botanical Society", Volume 97, July 1970
1989 George Bartunek (Geologist, Chairman of the Town of Riverhead Conservation Advisory Council)
"According to the `Soil Survey of Suffolk County' (USDA 1975) the area is classified as dune sand."--In a letter (July 10, 1989) to the Town Board and Planning Board of Riverhead
1998 John Black (Geologist, Professor Emeritus, Suffolk Community College)
"...examination of the area revealed that the Sandhills consist of...
... parabolic dunes perched atop a high bluff fronting on the Long Island Sound."-- "Long Island Botanical Society Newsletter", September Issue
Until this point there was no question as to the uniqueness of this site or the fact that dunes existed there.
Then a private firm began looking to develop the area. To do so the firm needed to produce an environmental impact statement
(EIS). The firm then looked to find consultants to write them the EIS. (Terchunian and
Sirken, 1999, see References).
The following account is New York State's response to this final environmental impact statement
1999 NYS Natural Heritage Program (A state biodiversity inventory; NYS Department of
Gregory J. Edinger (Community Ecologist) and Kathryn J. Schneider (Ph.D. Zoologist)
"throughout the FEIS the authors...criticize and make false statements... to refute well-documented information about important natural areas at the project site... They have used data to confuse decision-makers... The FEIS concedes that there are `wind blown soils' at the site, but later contradicts that view by stating `no maritime sand dunes exist' at the site."
--NYNHP Response to Final Environmental Impact Statement
BLACK, J.A. 1998. Geological aspects of the
Grandifolia Sandhills, L.I. Long Island Botanical
Society Newsletter. 8: 33-34.
FULLER, M.L. 1914. The Geology of Long Island,
New York. U.S. Geological. Survey Prof. Paper 82.
GAYES, P.T. AND BOKUNIEWICZ, H.J. 1991. Estuarine paleoshorelines in Long Island Sound.
Journal of Coastal Research SI #11: 39-54
GOOD, R.E. AND GOOD, N.F. 1970. Vegetation of the sea cliffs and adjacent uplands on the North
Shore of Long Island, New York. Bulletin of the
Torrey Botanical Club 97: 204-208.
LAMONT, E. 1998. The Grandifolia Sandhills; One of
Long Island's great natural wonders; Long Island
Botanical Society Newsletter. 8: 13-19
LEWIS, E., JR. 1876. The formation of sand-dunes:
Popular Science Monthly. 8: 357-363
LEWIS, R.S. AND STONE J.R. 1991. Late Quaternary
stratigraphy and depositional history of the Long Island
Sound Basin; Connecticut and New York. Journal of
Coastal Research SI #11: 1-23
SIRKEN, L.A. AND MILLS, H. 1975. Wisconsinan glacial stratigraphy and structure of northwestern Long
Island, in: Wolff, M.P., (Editor), Guidebook to field
excursions, 47th annual meeting, NYSGA, Hofstra
University, New York. 299-327
TERCHUNIAN, A.V. AND SIRKEN, L.A. 1999. DEIS.
Traditional Links LLC, Appendix 1. geology reports,
submitted to Town of Riverhead, New York. p.20
WASHBURN A.L. 1973. Periglacial processes and
environments: New York, St. Martins Press. p. 320
U.S. Coast and Geodetic Survey, 1834-38, Survey
Maps of Long Island, New York, Sheets T-52,53.
U.S. Coast and Geodetic Survey, 1885, Survey Maps of
Long Island, New York, Sheets T-1728
U.S.Geological. Survey, 1999, DEM based on
71/2' quadrangles, Riverhead and Gardiners Island East sheets
Direction of prevailing
Typical Parabolic Dune
Parabolic dunes are formed when wind causes
loose sand to coalesce into a mobile, crescentic-shaped
landform as above. Vegetation typically anchors the out lying perimeter causing "trailing tails".
Parabolic dunes are unique among the known range
of dune forms in that the relationship between
vegetation and dune appears to be causal. The importance of
plants to the formation of parabolic dunes can be inferred
by their complete absence on the otherwise dune-rich Desert Planet, Mars--where there are no plants.
Aerial photo of parabolic dunes at White Sands, NM. Wind direction is from lower
left to upper right. Note
how parabolic symmetry is dependant upon presence of vegetation. Conversely, see how other
dune forms are present where vegetation is absent.