Holocene Beach Ridges Research Articles

Sub-tidal ebb-shoal control of shoreline erosion via wave refraction, Magilligan foreland, Northern Ireland

A wave refraction model is used to examine the effects of sub-tidal ebb-shoal elongation on the erosion of the adjacent coast, at Magilligan, Northern Ireland. As deep-water wave approach angles are stepped at 10°-intervals from NW to NE, so the shoal controls the position of breaker convergence zones, which migrate NW along the shore but at a decreasing rate. Prolonged refraction of unidirectional swell is thought to be responsible for the formation of inshore sandwaves, which are known from previous studies (Carter, 1978) to promote differential erosion of the dune cliffs. However, longer-term changes in shoal geometry lead to shifts in the pattern of convergence and a general uniformity in erosion rates. It is surmised that the gradual development of the ebb-shoal and its consequential role in local wave refraction may have been a factor in the cessation of Holocene beach-ridge formation.

An 8,000-yr palaeoclimatic record of the ‘Double-Hale’ 45-yr solar cycle

A series of isostatically-emerged Holocene beach ridges on the east side of Hudson Bay have been precisely surveyed and dated back to 8,300 BP. They number 185 and show a nearly uniform rhythm of about 45 yr correlated here with the ‘Double-Hale’ solar magnetic cycle. (Time is in sidereal yr.) Longer correlations are suggested with eustatic sea-level curve and with planetary conjunction cycles. The coupling mechanism with terrestrial meteorological behaviour is believed to be by means of stratospheric generation of polar cirrus cloud and low-latitude ozone, affecting the planetary albedo.

Notes on late quaternary sea levels, Fiji and Rarotonga

Abstract Surveyed Holocene beach ridges near Taunova and Ndeumba, Fiji, have no accurate dates. Those at Ndeumba, where wind-blown sand may be absent, could represent high-spring-tide berms and they show that sea level has possibly fluctuated up to 3 ft above and 2 ft below the present within at least the later part of the Holocene. Radiocarbon dates for the 3 ft and 10 ft coral reefs at Rarotonga are 2,030 and 28,200 yr B.P. respectively, but because of recrystallisation these dates are most likely too young. A 6 ft terrace, probably younger than the 10 ft reef, is cut into older reef rock dated as greater than 48,900 yr B.P. A prograded strip of sand that almost completely encircles Rarotonga consists of storm ridges that are unsuitable for determining past sea levels. The oldest storm ridge has a radiocarbon date of 3,510 yr B.P. and is correlated with the oldest Holocene beach ridge in the Firth of Thames which has a radiocarbon date of 3,900 yr.