The coastline in the Jastrzębia Góra area can be divided into three major zones of general importance: a beach and barrier section, a cliff section, and a section protected by a heavy hydrotechnical construction. These areas are characterised by a diverse geology and origin, and hence different vulnerability to erosion. In addition, observations have demonstrated a different pace of erosion within each zone. Based on the results obtained by remote sensing methods (analysis of aerial photographs and maps), it has been determined that the coastline in the barrier area, i.e., to the west of Jastrzębia Góra, moved landwards by about 130 m, in a period of 100 years, and 80 m over about 50 years. A smaller displacement of the shoreline could be observed within the cliff. Between the middle of the twentieth and the start of the twenty-first centuries the shore retreated by about 25 m. However, in recent years, an active landslide has led to the displacement of the uppermost part of the cliff locally up to 25 m. Another issue is, functioning since 2000, a heavy hydrotechnical construction which has been built in order to protect the most active part of the cliff. The construction is not stable and its western part, over a distance of 50 m, has moved almost 2 m vertically downwards and c. 2.5 m horizontally towards the sea in the past two years. This illustrates that the erosional factor does not comprise only marine abrasion, but also involves land-based processes determined by geology and hydrogeology. Changes in the shoreline at the beach and barrier part are constantly conditioned by rising sea levels, the slightly sloping profile of the sea floor and low elevation values of the backshore and dune areas. Cliffs are destroyed by mass wasting and repetitive storm surges that are responsible for the removal of the colluvium which protects the coast from adverse wave effects. Presumably, mass movements combined with groundwater outflow from the cliff, plus sea abrasion cause destabilisation of the cliff protection construction.
Large group of the natural coastal landslides in the area of Gdynia (Babie Doły, Oksywie and Redłowo) are dominant and cover an area of about 4 ha (i.e. 60% of the area studied). The anthropogenic landslides, on the other hand, are more numerous but not bigger than 0.1 ha and occur within the town area. Cypel Redłowski is the most active cliff of the Bay of Gdańsk. There the erosion causes significant retreat of the coastline. The pace of that backward movement calculated by means of Terrestrial Laser Scanning (TLS), between years 2010 and 2015 was between 0 to almost 5 metres. During the same time the Cypel Redłowski retreated from 81.45 to 81.55 km, i.e. at a pace of 0.23 metres a year. The pace of retreat in the Cypel Oksywski was even faster in the past. There the active landslides caused total damage of the fortifications built at the beginning of the 19th century. Prevention against landslides caused by the marine erosion has been applied for over a hundred years now. The marine erosion is the most significant trigger of the coastal landslides. The intensity of the erosion depends on the frequency of storms. Heavy rains exceeding 100.0 mm per 24 hours also trigger mass movements in the Gdynia area. Such event took place in Gdynia in 2016. At that time a landslide movement causing extensive damage was recorded.
The climate variability and related sea-level changes during the Holocene are still under discussion, especially in a regional context. Very little information comes from the southern and south-eastern Baltic coast. The aim of the paper is to gain insight on the history of regional environmental changes, particularly sea-level and storminess, and their driving forces. The investigations were located on a peatland on the coast of Puck Lagoon (Gulf of Gdańsk, southern Baltic Sea). The analysis of peat core comprised: radiocarbon dating, analysis of stable isotopes 18O and 13C and chemical components, as well as palynological and diatomic studies. Results showed the 1.0 m peat section accumulated over 1500 years, with a time resolution of 100 years per sample. The average water level in the Puck Lagoon rose by ca. 0.85 m during the last 1500 years in a cyclic mode, with a period cycle of ca. 600–550 years and an amplitude not exceeding 0.5 m. The accelerated sea level rise and frequent storminess occurred during the first half of the Dark Ages (1500−1300 years b2k) and LIA (750−450 years b2k) and since the beginning of the 20th century. Recognized environmental changes are well correlated with both temperature changes in the North Atlantic and changes in total solar irradiance, suggesting synchronous Northern Hemisphere-wide fluctuations. The solar forcing was an important constituent of natural climate variability in the past and of forcing climate warming during modern times - after the Little Ice Age.
In the course of field work based on geo log i cal and land slide map ping and spa tial anal y ses of map in for ma tion at least 2 types of land slides were iden ti fied. Type I: sim ple land slides de vel oped in ho mo ge neous and un dis turbed rocks, for in stance -loams, clays and sands. This type of land slide in cludes many ex am ples de vel oped mainly on the stretch (seg ment of the stud ied area) ap prox i mately be tween 132.25 and 133.50 km and 128.50 and 129.50 km of the Pol ish coast line. Type II: complex land slides in which the move ment and dis place ment of rock masses oc curs un der com plex geo log i cal and hydrogeological con di tions. The com plex fac tors are de ter mined by phe nom ena such as glaciotectonics, dis con ti nu ities of rock lay ers and thrust zones; the slip sur face oc curs at con sid er able depths, and some times sev eral slip sur faces can be distin guished. These land slide types are lo cated in the vi cin ity of Jastrzêbia Góra and Rozewie, near km 134 and 131.5. Pre diction of the for ma tion of this land slide types is dif fi cult. Even if long-term ob ser va tions are avail able, the mass move ment, vari able over time, is dif fi cult to in ter pret. It is clear that the changes are con tin u ous, but oc cur with vary ing in ten sity. Proper rec og ni tion of the types of mass move ment is cru cial to es tab lish ing the ap pro pri ate meth ods to pre vent their de vel op ment.
The dendrochronological studies were carried out on very well preserved sub-fossil pine wood found in the biogenic deposits of the Rucianka raised bog (NE Poland). Local floating chronologies, covering the period 990-460 cal BC, were dated on the basis of radiocarbon analyses. Growth depressions in annual treering widths indicated periodical deterioration of the environmental conditions, which affected tree growth. Identified germination and dying-off phases (GDO) should be related to the wetter climatic periods. The extinction of trees took place during periods of higher groundwater level which, in turn, caused favourable conditions for growth of young pines.
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