Shores of the Laptev Sea
Shores of the Laptev Sea – stretch for 7,253 km. High ice coverage of the region limits the wave action to a great extent. Ice-free period in the western part of the Laptev Sea comprises 14 % and in the Eastern part 20 % of the whole number of days in the year. At the same time, storm upsurges and downsurges are quite big and their amplitude sometimes amounts to 5 m. They are to a large extent formed by loose marine, alluvial and marine, and alluvial and lacustrine–alluvial deposits. The latter are the deposits forming the so-called yedoma – the higher level of the tundra lowland plain presented by “a glacier complex” and characterized by a high concentration of dusty material and ice. Due to this the coastal plains are characterized by the relief of alases that is of cavities and lakes formed at the place of ground ice melting. Expansion of permafrost rocks accounts for their numerous exposures at the coastal area which influences thermo-abrasive processes here. These processes show themselves quite clearly in many coastal regions (Bykovsky Island and Muostakh Island, the Buor-Khaya Peninsula, etc.).
The continental coast of the Laptev Sea is often divided in two coastal areas according to the peculiarities of formation conditions. These are Lena-Anabar and Yana areas which are subdivided into Anabar, Terpyay-Tumus and Olenyok, Buor-Khaya, and Yana Districts. This scheme is completed by the districts of Bereg Pronchishcheva, the Khatanga Bay, and the Lena Delta.
The eastern lowland area of the coastal Taymyr known as Bereg Pronchishcheva is mostly formed by loose marine and alluvial deposits. Their width in rare cases amount to 180 m. In the southern part, the sea is approached by the exposures of sandstone and schists.
The northern parts of Bereg Pronchishcheva still preserve rugged shores with fjards, but here they are already influenced by wave action. In particular there are numerous offshore and island bars, the latter being more typical of the external parts of the islands lying close to the mainland coast. The bars consist of sand, gravel, and pebbles. The southern part of the coast that is being described here is characterized by alternation of straightened abrasive (and possibly thermo-abrasive) cliffs and small accretion forms like spits.
The shores of the Khatanga Gulf which presents a large estuary deteriorate under the action of thermo-abrasion. Along the cliffs close to the Khatanga mouth silt, foreshores are getting wider. They are obviously formed by water upsurges.
The Anabar District is marked by great development of abrasive shores. There are limited thermo-abrasive fields; in the west the waves deteriorate the bedding rock of Jurassic and Cretaceous periods. The straightened thermo-abrasive shore stretches from the Anabar to the Olenyok Gulfs. It is terminated by a wide accretion spit of Terpyay-Tumus formed by sand material. The northern part of this accretion peninsula is also subject to thermo-abrasion. The shore here draws back at a speed of 4 m/year.
The Anabar Bay is a tidal mouth of the Anabar River which does not have an estuary. But a small river named the Peschanaya forms an estuary protruding into the sea. The shore between Terpyay-Tumus spit and the Lena mouth has a complex structure. To the south of the spit, a small part of the fossil thermo-abrasive cliff is changed into an accretion field obtaining the material from rivers flowing down the slopes of Kryazh Pronchishcheva. Further there is a coast formed by alluvial upper quaternary deposits covered with permafrost. This is where the intensive retreat of the thermo-abrasive shore takes place. Further there is a multiarmed estuary of the Olenyok River protruding into the sea. To the east of this estuary, there is a small district of a foreshore changing into an abrasive steep cliff formed in Mesozoic terrigenous rocks, and after it there is an estuary of the Olenyok Protoka of the Lena Delta. This district can boast of frequent wind foreshores and barrier beaches.
The Lena Delta has an area of 28,500 km2. This is the largest delta on the coast of the Arctic Ocean. It is usually pointed out that it consists of two parts (eastern and western) formed in different times. However it would be more correct to divide the Lena Delta into three heterochronous parts: southern, western, and eastern.
The southern part includes the Olenyok Protoka of the Lena and Khardang-Sise Island. The region of this delta (that is close to Khardang-Sise Island) is the oldest. It is a butte of lower quaternary alluvial and deltaic plain. Certain parts of its surface lie at the height of more than 50 m. From the north it is separated by obsolete but contemporarily existing Arynskaya Protoka and from the south – by a large Olenyok Protoka which forms an independent stream flowing into the Olenyok Gulf. Its near shore zone is very shallow and abounds in islands and banks. Zaliv Kuba (Kuba Bay) between the estuary of Olenyok arm and the western part of the estuary is marked by a thermo-abrasive shore where the water erodes the upper quaternary estuary deposits covered by permafrost.
The western part of the Lena Delta is a large island named Arge-Muora-Sisse intersected by numerous obsolete creeks and speckled by thermokarst lakes. It is formed by frozen upper quaternary aleurite sediments. Many parts of the rugged sea coast of this island are subject to thermo-abrasive erosion. From the products of erosion working on the deltaic coast, the waved construct a large sandy island barrier consisting of several islands separated by straits. Their total length is more than 70 km. Besides to the north of it, there are two more island barriers (Samoleta Island and Aeros’emki Island), located at the edge of a shallow near shore zone. Along the edge of the part of the delta that is being described, there are numerous small islands, many of which seem to be buttes separated from the mainland part of the ancient upper quaternary delta due to the process of thermo-abrasion.
The eastern part of the Lena Delta is its current delta. It includes a plenty of islands and arms. When the floods are high, many islands get submerged. At the same time during seasonal floods, the island surface gets gradually higher due to the accumulation of silt depositions. Because of this rise, the islands gradually cease to be influenced by seasonal floods. Here at first gramineous and then dumetosous vegetation start to grow. Most of the islands are 5 m high and their surface currently presents a typical low-bush tundra. It must be noted that all large arms form stream–mouth bars with numerous midstream sandbank islands on them. These stream–mouth bars are usually cut by channels, the underwater continuations of the arms.
The surface of the Lena Delta is not only cut by many arms with the total length of 6,500 km but also speckled by a great number of lakes (more than 30,000). Ninety percent of them are shallow with an area of less than 0.25 km2. Most of the lakes and almost every large lake are situated in the ancient western delta which is obviously a consequence of long-term thermokarst processes in this area.
Buor-Khainskiy shore district begins with the Bykovsky Peninsula and the well-known Tiksi Bay. The Bykovsky Peninsula is formed by frozen sea depositions and is being actively eroded from the eastern side. One of the first discoveries of mammoth remains is known to have been made here in 1799. The remains showed up from the eroding thermo-abrasive shore. The land bridge connecting the submeridionally oriented part of the peninsula with the mainland possibly presents a tombolo with a lagoon in the northeast.
Intensive thermo-abrasive erosion is happening on a small island named Muostakh which lies to the south of Bykovsky Island. In the south end of the island, the erosion products from the northern shores of the island build a spit.
The western shore of Buor-Khaya Guba, a large bay that gave its name to this district, is formed by terrigenous deposits of Permian–Triassic period. In the regions formed by bedding rock, the shore is high and denuded, with avalanche and glide forms. The Khara-Ulakh River has a small promote estuary in the mouth of the bay. The shore here is clearly estuarine. To the north of this estuary, there is a small piece of the coast formed by frozen quaternary lacustrine–alluvial deposits subject to thermo-abrasion with clear-cut soliflual forms. In the apex of Buor-Khaya Guba, the shore is very shallow and has a clear-cut wind foreshore. This very type of shore can be seen still further to the north along the eastern shore of the bay up to the estuary of the river Omoloy. To the north of the Omoloy, there stretches a straightened thermo-abrasive shore with proofs of soliflual processes. The sand material outwashed from finely granular deposits of lacustrine–alluvial origin that form the Buor-Khaya Peninsula is moved by the waves to its northern end where it builds a looped spit diverging from the general direction of the coast to the east and the south.
The Yanskiy coastal district is marked by a large-scale compartmentalization of coastal line. To the east of the Buor-Khaya Peninsula, there is a significant indentation of the coastal line which is further changed into the river Yana estuary. Still further to the east, there are three large bays: Chondonskaya Guba, Sellyakhskaya Guba, and Van’kina Guba; to the north of the latter, there lies the Shirokostan Peninsula and the bay named Ebelyakhskaya Guba which protects the Svyatoy Nos Peninsula from the north. Further to the north, there is Dmitry Laptev Strait, connecting the Laptev Sea with the East Siberian Sea and separating the Lyakhovsky Islands.
The eastern shore of the Buor-Khaya Peninsula is more stable unlike the western one. Here predominant are obsolete thermo-abrasive cliffs with beaches and soliflual forms, and in the upper part of the abovementioned indentation of the coastal line, there is a shore with a wide wind foreshore.
The Shirokostan Peninsula is formed by frozen lacustrine–alluvial depositions of yedoma. Its shores consist of alternating thermo-abrasive areas and low accumulative areas with wind foreshores. Svyatoy Nos Cape is built from bedding rocks and has high steep abrasive shores.