DUNE: Not science fiction – It is EARTH science!
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Coastal sand dunes are a naturally occurring coastal earth feature. Dunes are typical features of Coastal stability and are part of the natural character of the coastal environment, which is protected under the Resource Management Act 1991 as a "Matter of National Importance". Natural character refers to the unmodified coastal environment.
Form and Function of Coastal Sand Dunes:
Sand dunes are formed at the interface between the sea and land – mounds or ridges of coastal wind blown sand that often form along coastlines in irregular rows or hills set back away from the water’s edge. Formed where constructive waves encourage the accumulation of sand which could be derived from terrestrial (for example: glacial or river) and/or oceanic sources (example: coral reefs), and where the prevailing winds blow this sand inland. The sand grains are then trapped by obstacles such as shell, debris, rocks or vegetation causing the sand to accumulate which starts the dune formation, growing or increasing by a slow process called accretion. The winds then start to affect the mounds of sand by eroding from the windward side and depositing them on the leeward (landward) side. Gradually this action causes the dune to “migrate" inland, as it does, it accumulates more and more sand. Sea Oats, with their deep root systems, and other native coastal plants help to anchor the dune and protect it from erosion. Dune vegetation grows upward with the dunes as they are continually buried by the dune’s vertical growth, further anchoring the dune. The form of dune systems will be dictated by a number of factors, including the shape of the coastline, shape of the beach, currents and swell of the ocean, prevailing wind, frequency of storm events, and particle size of the sand. Due to these same factors, the dunes are ever changing formations. Vegetation plays a major role in dune stabilization and growth.
Importance of Coastal Sand Dunes:
Coastal Protection: Dunes provide an essential first line defense acting as a buffer against winds and other forces such as storm waves and are a replenishing source of beach nourishment during periods of erosion/loss due to wave and current energies. It is important to maintain dune structural integrity to ensure that they continue to provide this form of protection. Dunes protect the inland properties not only against storm surge but severe winds also.
Water Quality: Coastal sand dunes act as filters for water, enhancing and maintaining coastal water quality.
Ecosystem/Habitat: Dunes act as Sand Banks to maintain the sedimentary and dynamic equilibrium of the dune and are rich in genetic diversity Dunes and their vegetation provide habitat for many different creatures and shorebirds including endangered species.
Dune Features:
There are different kinds of dune systems, and specific features of dune systems that can be identified.
Fore dunes: The most seaward zone of the dunes is the fore dune. It is characterized as a low, wind-deposited dune that is sparsely vegetated with the hardiest of dune stabilizing plants, ranging from well vegetated and stable to highly erosional. The incipient fore dunes are the newly developing dunes, not necessarily permanent features, initiated by wind blown sand being trapped by vegetation and other obstructing matter such as driftwood. These are the features that develop into established fore dunes. Established fore dunes develop from incipient fore dunes by steadily growing with sand collection on the seaward side. The leeward side then becomes more stable and with protection from salt spray and continued deposition of sand, the nutrient values of the sand/soil improve which supports more diverse vegetation, which in turn stabilizes the fore dune more. Many factors affect the morphology and development of fore dunes, such as: sand supply, type & amount of vegetation cover, wind & wave action, dune scarping and over wash processes, beach-surf zone type, commercial and residential development.
Dune crest: The dune crest is located behind the fore dune and may be identified by its higher elevation.
Back dunes: The back dune is a more stabilized coastal dune located behind the established fore dunes, is typically more stable and vegetated with a dense thicket of salt-tolerant shrubs. These dunes are still subject to accretion (steady growth by addition of sand) and erosion, but not to the same extent as the fore dunes. Also known as coastal strand, the back dune is probably the most rapidly disappearing type of dune because of its value as prime real estate for resort and residential development.
Blowouts: Depressions in the sand that can be cup/saucer or trough-shaped, caused by wind erosion of an existing sandy substrate. Cup/saucer shaped blowouts are shallow dishes and usually occur on flat/low dune terrain. Trough shaped blowouts are deeper with steeper erosional walls and are more elongated. There are three characteristics of blowouts: 1) Depositional Lobe; where sand from the walls and deflation zone is being deposited; 2) Deflation zone/basin; where sand has been scoured out. Often these reach the water table or the basal material (rocks). Both these factors prevent further erosion and revegetation often occurs; 3) Erosional walls; margins of the blowout. An incipient fore dune will often form across the throat of a blowout, reducing sand inundation and allowing revegetation.
Information is based on articles and data found @ the following sources: Wikipedia; Curiosity.com from Discovery; About.com; Coastal Sand Dune Form and Function. Patrick A, Hesp. CVDN Technical Bulletin No. 4. Forest Research, Rotorua.
DO NOT CLIMB OR ENTER THE DUNES ON FOOT OR BY VEHICLE! Dunes are a fragile and protected ecosystem and also contain venomous snakes. Leave no trace & Take only photographs!
In order to log this visit; please email answers to the following questions to the cache owner. Log may be deleted if it appears you did not actually visit the Earthcache coordinates. Thank you!
1. There is a very high peak to the south, viewed approaching the GZ coordinates from Hwy 361. This peak is an example of what type of dune feature?
2. Name the types of dune systems represented at this location.
3. What causes sand dunes to migrate?
4. How does the vegetation on a dune affect that dune?
5. What mile markers are on the beach and which direction from the access road are they?
6. Optional-post a picture of the dunes, this is a great spot for sunrise photos!
Beach Access Road 2. This is a public road open year-round except during severe and/or dangerous beach conditions. No permission is required for public road pull-off. Take care when parking or stopping, as there is always a risk of getting stuck in loose sand. Beach parking permits are required on the beach northward of this access, but free parking is available to the south of this entrance.
Congratulations to masseyfamily4 for being FTF and log this Earthcache!
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