Hutton Garnet Beaches
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OverviewThe Hutton garnet beaches are the result of wave action on eroded glacial till. Ocean conditions have resulted in extremely well-sorted sand deposits with high concentrations of heavy minerals, in some cases over 95%>3.2 specific gravity. Ocean sediments are also garnet-enriched. Marine studies conducted since 1999 indicate the sea floor to be flat and sandy for over 750 metres offshore.
In contrast to the red garnet sand, the inland terrain is grey and hummocky with many shallow ponds. This is interpreted as end moraine till from the Wisconsin (last) glaciation, derived from bedrock in the immediate area.
Primary rock types are Archean gneisses, largely overprinted with a high-pressure garnet-clinopyroxene granulite facies assemblage. For this reason, garnet is a dominant rock-forming mineral, and hills in the area have a reddish cast. Rocks contain up to 75% garnet.
After glaciers dumped garnet-rich till into the ocean, heavy minerals and sand particles were separated from fines by wave action, gradually collecting along the shore as beach sediments. Further concentration of garnet is ongoing daily in the swash zone: Waves deposit heavier minerals onshore and fines and lighter grains are washed (primary concentration method) or blown away (secondary concentration mechanism). Storm surge action concentrates garnet at the back of the beach by mechanical transport.
The sand deposition pattern is most likely influenced by longshore currents from the southeast, which carry ocean sediments northwards up the coast. Broad areas of accumulated sand, as near the Helga River, are evidence of this process.
The following paraphrases a recent report on the origin and conditions of the Hutton beaches by Dr. Catto, a well recognized expert in beach geomorphology.
Beach Regimes And DynamicsThe Hutton beaches are reworked glacial sediments deposited at the time of the melting of the Miriam Lake Valley glacier. This created a large fan delta complex from Hassell Head to 2 km south of the Helga River outflow, surrounding both the North and South Hutton beaches. Marine shells indicate the delta toe was underwater at the time of deposition. As sea level varied, sediments along the seaward edge were reworked by marine processes, as they continue to be today. Importantly, the Hutton heavy mineral sand deposits are geologically 'young' with sub-angular particles in contrast to the older, reworked South Asian and Australian alluvial deposits which feature well rounded grain shapes.
The sand deposits are classified as "sand dominated wide flats" developed on sediment substrates. Development of this type of system under a boreal to arctic climate in formerly glaciated terrain indicates relatively low energy and limited storm activity compared to a gravel-dominated system, with sediment supply considerably in excess of the amount removed by erosion and transportation. The presence of offshore seasonal ice reduces the period available for storm wave erosion. In addition, seasonal freezing and snow cover on the beaches limits the removal of sand during winter storms. The shallow offshore bathymetry, low energy levels, absence of large cusps and scoured channels and gently concave configuration of the shorelines, indicate that both North and South Beach can be considered as dissipative, low energy systems.
Individual beaches show indications of sediment transport along their lengths. The net transport of sediment takes place from south to north along both South Beach and North Beach.
In summary, the two beaches are modally relatively low energy systems protected from winter storms by seasonal ice and have abundant sediment supply. They are dissipative systems with shallow, gently sloping offshore bathymetry, dominated by shore-parallel transport.
South BeachThe South Hutton Beach is a baymouth bar system developed by dominant northward transport, essentially parallel to the shoreline, under low energy, largely dissipative conditions. The presence of offshore sand bars indicates that dissipative conditions are normally dominant. The beach widens to the north, and the outlet of Helga River has been displaced northward, as have the drainage channels for shallow ponds in the former lagoonal area. The alignment of the small spits and channels at the mouth of the river also indicate dominant northern transport. Aerial photographs indicate this direction has been generally maintained over the past 60 years since the first pictures were taken.
Small, laterally coalescent dome dunes and incipient parabolic dunes are present in the backbeach. The dunes appear to be generally stable or growing with local surfaces covered with some grass. The increase in height to 3 metres can be observed at the north end near the Helga River outlet.
The forebeach and nearshore areas are marked by ridge-and-runnel development, where garnet is concentrated on the ridges and runnels are infilled by quartz and feldspar. Difference in density and to lesser degree in grain size result in the segregation of mineral species into distinct bands. Differing wave energies associated with storm events are responsible for the formation of multiple bands of mineralogically segregated assemblages. Higher concentrations of garnet at some backbeach and upper forebeach sites reflect both residual lags of heavy minerals following winnowing of quartz and feldspar, and initial deposition during higher energy wave events.
The presence of concentrations of garnets in the active areas of the forebeach and in the nearshore zone, and their formation into constructional ripples and incorporation into cuspate features indicate that garnets are being actively transported into and within the South Beach system. The pattern of concentration around the Helga River mouth and along the river, with the highest concentrations generally seaward and successive layers of alternating garnet-rich and garnet-poor units exposed in cutbanks, indicate that the garnets did not originate from fluvial transport of Helga River. The vertical succession and variation in thickness visible in the cutbanks indicates that the garnets were transported from east to west, i.e. inland by wave action. The beach is growing because sediment influx is greater than the sediment erosion.
The variations recorded by the exploration programs and photographs suggest that there is sediment accumulation at the northern end of the beach system and there is net transport from south to north.
North BeachNorth Beach is an essentially independent system from the South Beach. Although some sediment from South Beach may eventually be transported to North Beach, the configuration of the northernmost part of South Beach in comparison to North Beach indicates that sediment is not directly transferred from one to the other, largely due to the rocky headland between.
North Hutton Beach is also a baymouth bar system developed by dominant northward transport, essentially parallel to the shoreline, under low energy, largely dissipative conditions. The beach widens to the north and the outlet of Howard Lake is located at the far northern end of the barrier system. This geomorphology, including the alignment of the small spits at the mouth of the Howard Lake outlet, indicates dominant northward transport. Hassell Head deflects the main flow of the coastal subcurrents associated with the Labrador Current offshore, shielding North Beach from the direct effects of the net southeastward flow. Sediment movement is generated primarily by waves generated from the southeast, counter to the modal direction of the offshore current. There is consistent northward direction of transport, and dome dunes and parabolic dunes are present in the backbeach area.
Garnet, feldspar and quartz distribution and concentration is similar to the situation described for the South Beach. The presence of concentrations of garnets in the active areas of the forebeach and in the nearshore zone, however, and their formation into constructional ripples indicate that garnets are being actively transported into and within the North Beach system.
The heavy minerals are less mobile and thus remain as lag deposits when moderate energy events rework the surface sediments. Higher concentrations of heavy minerals may result primarily from the removal of quartz and feldspar, rather than the deposition of greater amounts of heavy minerals.
Although there is net transport from south to north, the maintenance of geomorphology indicates that the amount of sediment influx to the southern end of the beach approximately balances the amount of transport to the north. At the northern end, sediment is currently accumulating, while the south part remains constant.
Seven Islands BeachSeven Islands Beach is a mid-bay bar system developed by dominant southward transport, essentially parallel to the shoreline, under low to moderate energy conditions. The beach is narrower and steeper than the Hutton Beaches. The beach widens from north to south, indicating a net southward transport direction. Because the beach is protected from eastern and southeastern winds by several islands -- including Amiktok and Whale Islands -- the wave reworking takes place only from the northeast.