Grzegorz Rachlewicz

26 December 2004 tsunami deposits left in areas of various tsunami runup in coastal zone of Thailand

The tsunami deposits left by the 26 December 2004 tsunami in the coastal zone of Thailand were studied within two months of the event and before any significant postdepositional changes could occur. The sediment structure and texture (grain size), as well as its thickness and spatial distribution, were documented for the tsunami deposits in 12 shore-perpendicular transects from areas of various tsunami run up and wave heights. The tsunami deposits were as thick as 0.4 m and were located as far as 1.5 km inland. They were composed mostly of poorly sorted sand and often consisted of one to four normally graded, massive or laminated layers. The deposits generally became finer in the landward direction; however, landward thinning trend of the deposits is not clear, and the maximum accumulation often is not located close to the shoreline but rather is further inland. In comparable coastal environments with similar available sediment sources the tsunami size (represented as the tsunami run up height) is reflected in the resulting deposits. Larger tsunamis are associated with deposits that are thicker, have a maximum accumulation located farther inland, include a finer sediment fraction (likely from deeper offshore areas) and frequently are composed of normally graded layers.

Variability of Water Chemistry in Tundra Lakes, Petuniabukta Coast, Central Spitsbergen, Svalbard

Samples of water from small tundra lakes located on raised marine terraces on the eastern coast of Petuniabukta (Ebbadalen, Central Spitsbergen) were examined to assess the changes in water chemistry that had occurred during the summer seasons of 2001–2003 and 2006. The unique environmental conditions of the study region include the predominance of sedimentary carbonate and sulphate rocks, low precipitation values, and an active permafrost layer with a maximum thickness of 1.2 m. The average specific electric conductivity (EC) values for the three summer seasons in the four lakes ranged from 242 to 398 μS cm−1. The highest EC values were observed when the air temperature decreased and an ice cover formed (cryochemical effects). The ion composition was dominated by calcium (50.7 to 86.6%), bicarbonates (39.5 to 86.4%), and sulphate anions. The high concentrations of HCO3 −, SO4 2−, and Ca2+ ions were attributed to the composition of the bedrock, which mainly consists of gypsum and anhydrite. The average proportion of marine components in the total load found in the Ebbadalen tundra lake waters was estimated to be 8.1%. Precipitation supplies sulphates (as much as 69–81%) and chlorides (14–36%) of nonsea origin. The chief source of these compounds may be contamination from the town of Longyearbyen. Most ions originate in the crust, the active layer of permafrost, but some are atmospheric in origin and are either transported or generated in biochemical processes. The concentrations of most components tend to increase during the summer months, reaching a maximum during freezing and partially precipitating onto the bottom sediments.