Sedimentary evidence of extreme storm surge or tsunami events in the southern Baltic Sea (Rogowo area, NW Poland)

Abstract

The Bal tic Sea is not typ i cally con sid ered as an area af fected by tsu na mis. How ever, dur ing the Late Pleis to cene and Ho lo cene sev eral tsu nami events have been in ter preted from the sed i men tary re cord, mainly in Swe den and Es to nia. Fur ther more, on the south ern coast of the Bal tic Sea, there are his tor i cal ac counts of catastrophical ma rine floodings called "der Seebär" ("the Sea Bear"). Their de scrip tions re veal many fea tures typ i cal for tsu nami, but their gen e sis re mained un known and sed i men tary ev i dence for such events has not been found. Here we pro vide ev i dence of sandy event lay ers from the area of Rogowo, NW Po land -the area of his tor i cal cat a strophic storms as well as "der Seebär" events. The study area is a low-ly ing coastal plain with an av er age el e va tion of -0.5 to +0.5 m a.s.l., pro tected from the open sea by beach and coastal dune sys tems up to 5 m high. Sedimentological, micropalaeontological and geo chem i cal anal y ses along with AMS 14 C dat ing were ap plied to sed i mentary suc ces sions seen in 5 ma jor trenches and 198 sed i ment cores up to 1.5 m long. Two sandy lay ers were iden ti fied in the peat de pos its that de vel oped on the plain dur ing the last ~2000 years. They re veal a num ber of typ i cal fea tures of tsu nami depos its (sig nif i cant lat eral ex tent and thick ness, rip-up clasts, chem i cal and micropalaeontological ev i dence of ma rine or i gin), how ever, 14 C dat ing along with the his tor i cal ac counts re vealed that the ma jor layer, ex tend ing at least 1.2 km from the mod ern coasts, was prob a bly de pos ited by ar gu ably the larg est storm surge dur ing the last 2000 years, which took place in 1497 AD. These storm de pos its were likely formed dur ing in un da tion of the low-ly ing coastal plain af ter ma jor breach ing of coastal dunes re sult ing in tsu nami -like flow pat tern and thus sim i lar sedimentological ef fects. A dis con tin u ous sand layer of youn ger age (18th cen tury) and shar ing sim i lar prop er ties to the pre vi ous one may be re lated to "der Seebär" event or an other storm surge. The study re vealed that the south ern Bal tic Sea coast may be af fected by much greater coastal flood ing than known from more re cent ac counts and ob ser va tions. Thus, the pre sented geo log i cal re cord should be taken as an ex am ple of a worst-case scenario in coastal zone risk as sess ment from nat u ral haz ards. These events left sed i men tary de pos its that re sem ble tsu nami depos its. It is likely that, in sim i lar set tings where storm surges cause uni di rec tional in un da tion of a coastal plain, it may not be pos si ble to es tab lish whether the re sult ing de pos its were laid down from storms or tsu na mis.Key words: tsu nami de pos its, storm surge de pos its, grain size anal y sis, geo chem is try, ra dio car bon dat ing, Bal tic Sea.

Modern and historical tropical cyclone and tsunami deposits at the coast of Myanmar: Implications for their identification and preservation in the geological record

“…However, the sand sheets are composed of one massive to normally graded unit, while evidence of planar lamination, which is assumed to be rather typical for tsunami deposits, is missing (Morton et al ., ; Szczuciński et al ., ). The lack of lamination may imply unidirectional flow conditions similar to those during tsunami inundation, which here might have been caused by an abrupt discharge of elevated water levels seaward of the coastal barrier into the low‐lying depression behind (Piotrowski et al ., ). An alternative explanation could be post‐depositional processes, since lamination is masked after only a few years under a tropical climate (Brill et al ., ).…”

“…This may be explained by the considerably lower coastal barrier compared with CHA and NGW. Here, rising of water levels significantly above the back-barrier level prior to barrier inundation is not possible (Piotrowski et al, 2017).…”

Ģeogrāfija, ģeoloģija, vides zinātne : Latvijas Universitātes 76. zinātniskā konference : referātu tēzes

“…This latter group likely suggests a storm record, where grain damage results from a very energetic subaqueous environment (Gutiérrez-Mas et al 2003), and is additionally supported by presence of coarser interlayers (cf. Piotrowski et al 2017). In the uppermost and middle horizons, a number of grains with conchoidal features is limited, and grains from the first group dominate.…”

Natural Hazards and Extreme Events in the Baltic Sea region

“…While there are few surviving sea level measurements or other historical records dated before the 19 th century traces of extreme floods are found from sand layers. Studies of coastal sediments, compared with historical records, imply that the flood in 1497, which damaged cities on the southern Baltic coast, was the largest storm surge on the Polish coast in years (Piotrowski et al, 2017). St. Petersburg has also proved vulnerable to coastal and fluvial flooding, and the highest documented surge occurred in 1824, when the water level rose to 367 cm at Kronstadt, and possibly even to 410 cm at St. Petersburg (Bogdanov and Malova, 2009) over local mean sea level.…”