18th October

The 'real' map of Inisbofin

Eoin Mac Craith, GSI

In July 2012, the Geological Survey of Ireland vessels RV Keary and RV Geo arrived at Inishbofin, off the coast of Co Galway, with the goal of mapping the underwater terrain surrounding the island. This work took place as part of the INFOMAR seabed mapping programme ― a national project that ultimately aims to map all of Ireland’s inshore waters and offer the data freely available to the public.

INFOMAR Bofin jpg

RV Keary is a 15m aluminium catamaran purpose-built for inshore mapping, while RV Geo is a 7.5m RIB (Rigid Inflatable Boat) used to enter very shallow water adjacent to intertidal areas and to put the finishing edges to INFOMAR’s marine maps.

Latest technology

These vessels are equipped with modern sonar survey systems that reveal the underwater landscape beneath them as they move back and forth, progressively mapping a given area in a series of parallel tracks. This was to be the first time that Ireland’s national marine mapping project, INFOMAR, carried out a seabed survey encompassing an island.

The seabed survey has primarily focused on 26 priority bays and 3 priority areas around the Irish coast, each selected due to its importance for a variety of maritime factors. What makes island mapping distinctive however is that it is essentially the inverse of mapping a bay.

Testing conditions

Rather than survey vessels steaming up and down a grid of planned lines within the confines of a sheltered bay, at Inishbofin, for example, they found themselves in an open, unforgiving sea, circumnavigating a rugged island on the western edge of Ireland, hugging its coast as large swell waves crashed on exposed cliffs and jagged rocks around them.

Inishbofin’s island community is famously welcoming, helpful and resourceful. They were a great help to the crew as they sought anchorages, harbour berths, accommodation and supplies. Without their help, the survey would have been much more difficult.

The island’s coastline and inshore waters however presented a difficult challenge in terms of safe navigation and the vessels’ ability to gain sonar coverage of its surrounding seafloor.

Greeting an Atlantic swell that rarely relented in its attack, Inishbofin’s craggy coast was a labyrinth of shallow, hidden rocks, gullies, blowholes and ravines. While RV Keary navigated the waters further out from the island and mapped over a larger scale, itself carefully mapping shallow breakers and hidden rocks, RV Geo skirted closely along these coastal features in an effort to produce the most complete survey possible of this fascinating and complex seabed.

The RIB made use of high tides to gain access to areas that would otherwise be too treacherous, from steeply-sloping beaches to shallow, rocky reefs. The final result was a striking, three-dimensional map of the seafloor surrounding Inishbofin and its neighbour, Inishark.

Spanning a depth range from zero to a hundred metres, with plains of gently undulating sediment separated by rugged, fractured and faulted outcrops of bedrock, this area of seabed is a varied and contrasting underwater world – much like Inishbofin itself.

Perhaps now the ‘real’ map of Inishbofin will be a useful tool for the people to present their rich and diverse island to visitors in the context of its equally majestic maritime landscape.

The survey data are freely available for download at www.infomar.ie.

Note: As an adjunct to the published ‘real’ map of Ireland showing Irish seabed territory extending to ten times the country’s landmass, the crew of the survey vessels decided to square off the island with additional coverage, allowing for a more complete overview of the seabed around Inishbofin as seen in the attached image.

Spread the News