S. Dawson

Coastal sedimentation associated with the June 2nd and 3rd, 1994 tsunami in Rajegwesi, Java

Abstract This paper presents the second detailed study of sediments deposited by modern tusnamis, the first being that of the Flores (Indonesia) tsunami of December 1992 (Shi et al., 1995). Sediment cores were collected from areas in which eyewitnesses reported sediment deposition. Grain size analysis shows pronounced vertical variations in grain size as well as changes in standard deviation, skewness and kurtosis that appear to be indicative of complex tsunami flooding. Vertical variations in grain size in individual cores are greater than spatial variations between cores taken along a transect completed perpendicular to the coastline. The Java tsunami-deposited sediments do not show unequivocal evidence of local erosion but instead evidence for sediment transport and deposition is clear and is characterised by dominantly unimodal sediments with fine-tailed distributions.

Record‐breaking height for 8000‐year‐old tsunami in the North Atlantic

One of the largest Holocene sub-marine slides mapped on Earth is the Storegga slide offshore Norway [Bugge, 1987] (Figure 1). Approximately 3500 km3 material slid out and generated a huge tsunami dated to about 7300 14C yr BP [Bondevik et al., 1997a], or ca 8150 calendar years BP. The tsunami is known from onshore deposits in Norway [Bondevik et al., 1997a], on the Faroe Islands [Grauert et al., 2001], and in Scotland [Dawson et al., 1993]. Of these, the tsunami deposits in western Norway reaches the highest elevation, indicating a runup of 10–12 m. In this article, we demonstrate that at the Shetland Islands between Norway and Scotland (Figure 1), this tsunami reached onshore heights at least 20 m above the sea level of that time.

The sedimentology of Middle Holocene tsunami facies in northern Sutherland, Scotland, UK

Abstract Lagoonal sediments attributed to the main Holocene marine transgression in Strath Halladale, northern Sutherland, contain a complex coarser layer believed to have been deposited during the tsunami associated with the Second Storegga Slide off South West Norway. The coarser sequence is dated at between 7590±50 and 7290±50 radiocarbon years BP (6507–6260 cal BC and 6228–6029 cal BC). Detailed stratigraphical analysis has determined a distinctive suite of sedimentary sub-units within the coarser layer in marked contrast to the sediments, which occur above, and below. A pronounced erosional unconformity with the underlying sediments is recorded with the base of the tsunami layer characterised by eroded material from the underlying peat. The presence of a mixed diatom assemblage, although fragmentary, indicates a chaotic accumulation of the deposit with all habitats represented. Variations in particle size within the sequence disclose striking similarities with those from contemporary tsunami deposits. The run-up of the tsunami sediments is calculated at a minimum of 4.6xa0m. This is the first occasion on which a deposit of the Second Storegga Slide tsunami has been found outside the North Sea basin and indicates that the area affected by the tsunami may have been larger than has been previously described.

Holocene relative sea-level changes on the margin of a glacio-isostatically uplifted area: an example from northern Caithness, Scotland

Evidence is presented for Holocene relative sea-level changes on the margin of a glacio-isostatically uplifted area: the lower Wick River valley, northern Caithness, Scotland. Lithostratigraphic, biostratigraphic and chronostratigraphic analyses of intercalated clastic and organic sediments disclose evidence for a rapid rise of relative sea level from at least as low as -3.6 m to +1.5 m O.D. during the mid-Holocene, culminating between c. 6900 and c. 5900 BP. This is correlated with the Main Postglacial Transgression, identified widely in eastern Scotland. Following a subsequent regression, the sediments record two further marine transgressions beginning at c. 4400 and c. 1200 BP. The presence of late-Holocene estuarine deposits as the highest Holocene marine sediments is a situation only recorded to date at one other site in mainland Scotland. The coastal sediment sequence also indicates evidence for a palaeotsunami that occurred at between c. 7300 and c. 7000 BP and was associated with the Second Storegga Slide, one of the worlds largest submarine sediment slides, located on the continental slope west of Norway.

The diatom biostratigraphy of tsunami sediments: Examples from recent and middle holocene events

Abstract The interpretation of diatom biostratigraphy is a little used technique in the study of onshore tsunami sedimentation. Evidence is presented from examples from three tsunamis in which sediments were either observed to have been deposited; documentary evidence attests to the presence of sediment sheets, or finally, in the case of palaeo tsunamis, morphological and stratigraphical evidence permits the interpretation of tsunami inundation and the subsequent deposition of sediment. Examples from Scotland and Canada, and preliminary results from Indonesia, illustrate distinctive diatom assemblages that are associated with tsunami sedimentation. These assemblages contrast with the sediments immediately underlying and overlying the tsunami sediment. Data is presented showing an often chaotic assemblage, attributable to the tsunami waves crossing many distinctive diatom habitats, from fully marine planktonic and benthic species, through the varied intertidal zone and finally over the onshore terrestrial environments. The deposits attributable to tsunami inundation, particularly in Scotland, disclose a high proportion (often in excess of 65%) of broken diatom valves, and an over-representation of centric species due to their greater resistance to erosion. Together the information derived from known historical tsunamis and from palaeo tsunamis with good stratigraphical and dating control provide a good basis for the study of the diatom characteristics of modern tsunamis.

Holocene relative sea levels and coastal changes in the lower Cree valley and estuary, SW Scotland, U.K.

Changes in Holocene (Flandrian) relative sea levels and coastal geomorphology in the lower Cree valley and estuary, SW Scotland, are inferred from detailed morphological and stratigraphical investigations. A graph of relative sea level changes is proposed for the area. Rising relative sea levels during the early Holocene were interrupted at c . 8300–8600 14 C years B.P.( c . 9400–9900 calibrated years B.P.), when an extensive estuarine surface was reached at c . −1 m O.D., after which a fluctuating rise culminated at c . 6100–6500 14 C B.P. ( c . 7000–7500 calibrated years B.P.) in a prominent shoreline and associated estuarine surface measured at 7·7–10·3 m O.D. A subsequent fall in relative sea level was followed by a rise to a shoreline at 7·8–10·1 m O.D., exceeding or reoccupying the earlier shoreline over much of the area after c . 5000 14 C B.P. ( c . 5,800 calibrated years B.P.), before relative sea level fell to a later shoreline, reached after c . 2900 14 C B.P. ( c . 3100 calibrated years B.P.) at 5·5–8·0 m O.D., following which relative sea levels fell, ultimately reaching present levels. During these changes, a particular feature of the coastline was the development of a number of barrier systems. The relative sea level changes identified are compared with changes elsewhere in SW Scotland and their wider context is briefly considered.

Holocene relative sea-level change in the lower Nith valley and estuary

Synopsis Detailed morphological, lithostratigraphical and biostratigraphical studies in the lower Nith valley and estuary, Scotland, disclose evidence for changing relative sea levels during the Holocene. The Main Postglacial Transgression was in progress in the area around c. 7500 14C years bp (8350 cal. years bp) to c. 7800 14C years bp (c. 8600 cal. years bp), perhaps by c. 7675 14C years bp (c. 8490 cal. years bp); relative sea levels fell briefly after c. 7200 14C years bp (c. 8020 cal. years bp); then resumed their rise after c. 7000 14C years bp (c. 7800 cal. years bp) and culminated by c. 590014C years bp (c. 6720 cal. years bp) reaching the Main Postglacial Shoreline, the evidence for which is widespread in the lower Nith valley. Subsequently, relative sea levels may have fluctuated, modifying or exceeding Main Postglacial Shoreline features along the estuary coastline before falling to a lower shoreline and then falling farther to reach present levels at c. 1760 14C years bp (c. 1800 cal. years bp), after which there is no evidence for relative sea-level change in the area. This sequence is considered broadly comparable with sequences recorded at other sites along the northern shore of the Solway Firth, in particular confirming evidence for a fluctuation in the Main Postglacial Transgression and for the age of the Main Postglacial Shoreline.

Intertidal peat deposits and early Holocene relative sea-level changes, Traigh Eileraig, Isle of Coll, Scottish Hebrides

Synopsis An intertidal organic deposit is described for Traigh Eileraig, Isle of Coll, Scottish Inner Hebrides. The organic sediments are overlain by sands containing marine diatoms. Radiocarbon dating and diatom analysis indicate that a relative marine transgression took place in Coll at c. 8000 14C years bp, an interpretation consistent with the results of pollen analysis of the organic material. The age and biostratigraphical interpretation of this relative marine transgression is in agreement with the results of sea-level research undertaken in recent years at Arisaig, western Scotland. However, the altitude at which the early-Holocene relative marine transgression is recorded in Coll is significantly lower than Arisaig, this difference reflecting the influence of differential glacio-isostatic uplift across the Inner Hebrides.

Lateglacial climate change and coastal evolution in western Jura, Scottish Inner Hebrides

The geomorphic and sedimentological evidence for former sea-level changes in the exposed coastline of western Jura shows a clear coastal response to past changes in climate. In particular the rapid and high-magnitude climate changes associated with the onset and termination of the Younger Dryas appear to have been accompanied by major changes in coastal response. In western Jura, the temperate climate of the Lateglacial Interstadial was associated with beach-ridge deposition, with the earlier part of this period being associated with larger ridges than the latter. By contrast, the cold climate during the Younger Dryas appears to have been dominated by frost processes, sea-ice development and rapid rates of coastal erosion of bedrock. Cold-climate shore erosion of bedrock appears to have ended suddenly at the close of the Younger Dryas.