Iceberg Ploughmarks

Abstract

Iceberg ploughmarks are caused by icebergs that ground on the seafloor. Today, icebergs are very rare in Irish waters. This, however, was not always the case. During past glacials (e.g. 20,000 years ago) numerous icebergs reached Ireland’s shores leaving their marks on the seabed (Fig. 11.1). Typically, icebergs are moved either by ocean currents or winds. Once grounded, the bottom of the iceberg scraps the seabed as the iceberg continues to move. High tides can lift the icebergs temporarily clear of the seabed but often dropping them again before they have had a chance to move very far, in many cases they are merely moved upslope into even shallower waters. Melting of icebergs reduces their draft thus allowing the iceberg to either drift away or get dragged even further up the slope. The result is that icebergs leave marks in the soft sediments of the seafloor that usually follow gentle zigzag lines climbing up the slopes (Fig. 11.2–11.4).