NATURALNE I ANTROPOGENICZNE PRZYCZYNY POWSTAWANIA I REAKTYWACJI RUCHÓW MASOWYCH NA OBSZARZE MIEJSKIM GDYNI ORAZ ZWIĄZANE Z NIMI ZAGROŻENIA

Abstract

CAUSES OF NATURAL AND ANTHROPOGENIC MASS MOVEMENTS IN GDYNIAAbstract. 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.