Causes of Natural and Anthropogenic Mass Movements in Gdynia

Abstract

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.

Landslide susceptibility mapping of Gdynia using geographic information system-based statistical models

“…The earliest information on threats related to mass movements in the area of present-day Gdynia dates to the end of the sixteenth century and relates to cliff coasts (Małka 2019). The maximum annual shoreline recession in the second half of the nineteenth century was 2 m. Currently, the maximum shoreline recession is 1 m per year (Małka et al 2017). Landslides on cliff slopes are usually activated several times a year; these are typically successive and deep-seated.…”

“…Currently, urban development is progressing into the moraine plateau area, which is characterized by significant change in elevations, resulting in strong transformations of the relief. At the turn of the twenty-first century, intensive urban development combined with an increase in the frequency of extreme hydrometeorological events contributed to a decrease in slope stability (Małka et al 2017), leading to a significant increase in landslide risk, which is associated with an increase in both the number of hazards and the elements at risk (Aleotti and Chowdhury 1999). Unlike the landslides on cliff slopes, inland landslides are shallow at approximately 2-3 m (Małka et al 2017;Małka 2019).…”

“…road and construction works), redirecting rainfall-runoff in such a way that the flow is concentrated, adding water to the slope by irrigation, and land cover changes (e.g. deforestation), or a combination of natural and anthropogenic processes (Małka et al 2017).…”

“…For example, considerable destruction occurred within the city after heavy rainfall in July 2016. The damage included failure of infrastructure embankments (railways and roads), damage to and burying of several buildings, shifting and cracking of retaining walls, destruction of a car park, burying of cars, destruction of a bridge, destruction of stairs descending on to the beach, and destruction of a playground (Małka et al 2017). In February 2017, after rapid warming, a road was destroyed, a historic villa and a car were buried following a landslide in Kamienna Góra (Fig.…”

“…Thus far, the mass movements in Gdynia have not resulted in any casualties. However, considering their dynamic characteristics (velocity of 5-15 m/s), they could prove fatal in the future (Małka et al 2017;Małka 2019).…”