Shores of the Chukchi Sea
Shores of the Chukchi Sea – a vast system of lagoons and barriers. The most important conditions of the shore formation are the shelf character of the sea, severe climate, difficult ice conditions, a small degree of compartmentalization of the coastal line, and the peculiarities of the coastal land relief. These peculiarities are as follows: the sea is approached either by the offshoots of the coastal pressure ridge formed by the slate–limestone complex of the Paleozoic period or by the narrow lowland separating the mountains from the sea and formed by loose depositions of different origin (mostly lacustrine–alluvial and marine). This lowland is covered by permafrost. The winds and subsequently the waves spread predominantly from the north to the northwest.
The shores of the western and central coast of the Chukchi Sea in the region of Cape Schmidt and Cape Vankarem are characterized first of all by great development of the shore bars and lagoons separated by them. Their natural borders are Mys Yakan (Cape Yakan) in the west and the Serykh Gusey Islands in the east. The shore from Cape Billings to Cape Schmidt is straightened along the length by offshore bars and barrier spits. The only exception is Cape Schmidt, formed by traprock, quartz porphyry, and albitophires. The peculiarities of barrier spits are, firstly, that they are very large (e.g.,, the barrier spit of the lagoon Tenkergynpilgyn is about 100 km long) and, secondly, they are formed by pebbles and gravel from rock debris originating from the mountains away from the coast, that is, the products of fluvial forms abrasion currently partly flooded and frequent on the sea bottom. This proves that these barrier spits are formed mainly due to settled bottom sediments. The barrier spits often include bedding rock buttes.
On the offshores of all the barrier spits, it is easy to see a step of abrasion at the depth of 4–5 m which is interpreted as a trace of the barrier spit shift in the direction of the land under the influence of the waves.
The lagoons are also quite unique. Their mainland shores are usually high and formed by permafrost rocks. Under the warming influence of water and atmosphere, there starts a process of thermal abrasion and thermal denudation of these steep shores, and there develop soliflual phenomena on a great scale, that is, the flow of table soil.
Another peculiarity of lagoons is their stretching along the general direction of the shore, along the direction of the predominant local winds which even not being parallel to it far from the shore obtain the same direction as soon as they reach a lagoon surface. Some lagoons (Amguema, Pyngopilgyn) in their configuration are rather limans than lagoons. They are along with other limans the result of water logging of the lower reaches of the river and the subsequent cutoff of the bay that has been formed.
The eastern entrance Cape of Kolyuchinskaya Guba presents Belyaka Spit. All the other shores of Kolyuchinskaya Guba are not high, though steep. These are thermo-abrasive soliflual cliffs with the exception of several accumulative forms like spits. The abovementioned cliffs serve as the areas of buildup for these spits.
The head of Kolyuchinskaya Guba is marked by the development of foreshores. Originally Kolyuchinskaya Guba is a large liman created as a result of the sea ingression into the Ioniveyem River and its tributaries. The bay is shallow, and its head gets shallow in an especially intensive way as local waves stimulate beach drifts directed southward and at strong upsurges created by north and northwestern winds.
Belyaka Spit is a large accretion form morphologically resembling a double barrier. The geological structure of the second branch of Belyaka Spit is that of an original peninsula formed by frozen argillaceous and sand–loam deposits of the plain which genetically belong to glacial sea depositions. Belyaka Spit itself is a free accumulative form that was formed due to the beach drift directed westward. The source for buildup of this spit is the material borne due to abrasion of a small thermo-abrasive soliflual cliff lying to the east of this spit and Mys Dzhenretlen (Cape Dzhenretlen) formed by granite gneisses that are intensively eroded here. The offshore is formed by badly sorted sand and pebbles and even rubbly material which was obviously washed out by waves, while thermo-abrasive erosion of glacier and sea sediments had formed the retreated shore.
The movement of the material westward to Belyaka Spit is due to the significant deviation of the shore configuration from its general course, thanks to which the energetic resultant of the waves obtains the direction favorable for the transfer of material to the west, to the mouth of Kolyuchinskaya Guba.
To the east of Mys Dzhenretlen, there is a lagoon named Neskynpilgyn with low abrasive shores. At the entrance to this lagoon, there forms a small spit, but the main part of the barrier separating the lagoon from the sea is formed by argillaceous glacier and marine depositions that are badly sorted. This barrier is subject to thermo-abrasion from the lagoon. From the side of the sea, a part of this barrier is protected by a mixed sand and shingle bar separating a narrow lagoon. Genetically the Gulf of Neskynpilgyn should be obviously considered a liman which formed as a result of the sea ingression into the valleys of several small rivers which are now flowing into the gulf.
The promontories formed by Cape Nettan, Cape Serdtse-Kamen, and Cape Ikigur and located to the east of the Lagoon Neskynpilgyn are made of granites and syenites. Granite shores are usually subject to very slow sea erosion. The main factor in erosion of this part of the shore as well as in debris flowing into the littoral zone is denudation processes: landing slips, sloughing of the debris formed as a result of mechanical weathering. Between Cape Ikigur and the limans of the Inchoun River, the shore is straightened, abrasive, and formed in shale phyllitic metamorphosed rock.
Cape Dezhnev is formed by granites, quartz, and nepheline syenites. The shore here is eroded to quite a small extent. The cape is more than 740-m high; it is very steep and more sloping in the west. Between Cape Inchoun and Cape Dezhnev, there is Uelen Lagoon consisting of two heterogeneous areas. Its southwestern part presents a liman and the area stretching along the shore is a lagoon proper. The barrier spit of the lagoon is formed predominantly by pebbles and has a steep continental slope. It was presumably formed, like other barrier spits of the Chukotka coast, due to the bottom deposits, but at the moment is being build up by alongshore depositions, judging by the orientation of the wave resultant.
Generally the coast of the Chukchi Sea is the largest region of the lagoon coast in the Arctic Ocean.
Northern Alaska, a significant part of which is washed by the waters of the Chukchi Sea (from Cape Prince of Wales to Cape Barrow), is located in the zone of Cimmerian Orogeny. Here the scientists single out three main structural elements: the Yukon Massif, the upheaval of the Brooks Range, and Colville deflection. The Seward Peninsula lying at the beginning of the Chukchi Sea coast of Alaska belongs to the massif. It submerges to the north and to the east creating a depression occupied by Kotzebue Sound and its coastal plain. The relief of the Seward Peninsula is of middle altitude (maximum height is 1,445 m) and of hummocky topography, mostly lytomorphic with the traces of ancient mountain glaciation.
The Brooks Range consisting in the western part of two mountain chains – De Long and Bird – almost never approaches the seashore, except some capes in the zone of the western immersion of the uplands.
Colville depression is a submontane depression advancing to the Brooks Range. It is formed by Mesozoic deposits and in the coastal area manifests itself in the relief as a broad coastal tundra plain exceeding eastward the boarder of Alaska and joining here with the estuary of the biggest Canadian river Mackenzie. The biggest part of this plain forms the coast of the Beaufort Sea.
The shore of the Chukchi Sea within Alaska begins with Cape Prince of Wales. This is an intrusive granite massif, rising 700 m above the sea level like Cape Dezhnev. This is a typical denuded shore with sloughing and gliding masses accompanying it. Further to the northeast, there stretches a straightened coast formed by the largest offshore bar which is partly an island one with the total outstretch of 200 km separating lagoons Long, Arctic, and Shishmaref Inlet.
The above mentioned bar finishes at the entrance to Kotzebue Bay with Cape Espenberg. The shores of Kotzebue Sound are almost entirely thermo-abrasive except the area close to the mouth of the Kobuk River, presented by the mouth of this river.
The characteristic of the Seward Peninsula coast is its terracing. Here there are terraces at the height of 7, 12, and 24 m and on the continental slope – at the depth of 6 and 10 m. American scientists speak about six transgressions in Pliocene quaternary period which left their traces in the form of depositions and marine terraces. The latest of them named Kruzenshtern transgression left its terrace at the height of 2–4 m and is 4,000–10,000 years old.
The main element of Cape Kruzenshtern is a mixed sand and shingle bar 18 km long and 0.1–3 km wide. In the broad areas, the microrelief of the bar’s surface is formed by more than a 100 beach ridges separated by swamps and lagoons. The youngest ridge approaches a currently existing beach and is home to a camp of the Eskimo. The most ancient of them keeps archeological material that makes it possible to date them back to 4,000 or 5,000 years ago.
The coast from Kotzebue Sound to Cape Hope is straightened, complex, and accretion-thermo-abrasive. Cape Hope is a mixed sand and shingle bad blocking the entrance to the lagoon. To the north of Cape Lisburne, there stretches a slightly sloping bow of a straightened thermo-abrasive coast. Cape Lisburne is formed by Paleozoic metamorphosed rock and is structurally connected with the western depression of the Brooks Range. The coast here presents a high cliff (up to 300 m high) and can be classified as abrasive and denuded. The same is true for Cape Thompson where the coast is built from grit in the area covering 30 km.
Between Cape Lisburne and Cape Barrow, the shore is very versatile. Its contour includes several intersecting bows. The southern bow, right to the east of Cape Lisburne, is a straightened thermo-abrasive and soliflual shore. This indentation into the coastal contour changes into a convex bow of an island bar, which separates the Kasegaluk Lagoon and stretches up to Icy Cape where this bar joins another which is an element of the following concave bow of the coastal contour. This bow ends with the barrier spit Franklin which separates Peard Bay from the sea. From this bay to Cape Barrow, there stretches one more concave bow which is fully thermo-abrasive.
Thermo-abrasive areas of the coast are formed by loose shore marine deposits, from aleurites to gravel with cavern-load ice insertions. The sea cliffs reach 9 m in height and the speed of shore retreat amounts to 3 m/year. The plain is marked by total absence of glacier depositions. From time to time in the middle of the tundra, it is possible to see pingos (bulgunnyakhs).
Island barriers account for 58 % of the total length of Alaska northern coast. First of all this is due to favorable wave conditions between Point Lay and Cape Barrow, as the Chukchi Sea here is free from ice at least 3 months a year. This is the time of prevailing winds which account for the waves approaching the coast at a right angle. The geological and geomorphological conditions are not less favorable. The shallow continental coast presents a submerged plain formed by loose bottom settlings consisting of coarse sand, gravel, and pebbles. The island barriers to the south of Icy Cape are very prominent. Here there are seven islands with the total length of 120 km and the barrier width reaches 350 m while the islands’ height is 2–3 m. The islands are formed by sand and gravel, thrust over lagoon aleurite sediments. The continental slopes of the islands are marked by fine-grained sand. There is an obvious tendency to the movement of the islands toward the land. To the north of Icy Cap, the barrier islands are lower and narrower.
What is peculiar about these barrier islands or island barriers is their moderate width and height. This proved quite clearly that they were formed after the Holocene transgression of the World Ocean as all the islands and island barriers, formed at that time and belonging to relict formations at the present moment, are 5–7 m high.