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Blacksod Bay

Overview

Blacksod Bay is located on the Atlantic coast, north Co. Mayo in the north-west of Ireland. It is orientated north/south with the southern end open to the Atlantic and the northern end linked to Broadhaven Bay via a small man-made channel.

Click image for more detailed map.

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INFOMAR Survey History

The Celtic Voyager mapped a large portion of the deeper water between Achill Island and the Mullet Peninsula in 2008. The RV Geo, RV Keary and Cosantóir Bradán focused their efforts on the shallower waters in the bay in 2010, 2011 and 2014. The Celtic Voyager returned again in 2016 to map more of the deeper water around the Black Rock area.

Lidar surveys were completed in 2008 by Tenix LADS and in 2010 by Pelydryn. The seabed is prominently sand which enabled good laser penetration and depth returns in excess of 25m at the mouths of the bay. Blacksod Bay was flown to overlap with the existing 2006 LADS LiDAR survey at its southern end. Blacksod and Broadhaven Bays were flown as a combined survey.

Click image for more detailed map.

Survey Coverage polygons can be downloaded as a shapefile from our Interactive Web Data Delivery System (IWDDS).

Select your area of interest. Vector datasets - Offshore - Offshore Shapefiles

Read more about some of the survey legs on our Blog by clicking on the links below.

KRY10_04 Blacksod Bay

2010 LiDAR Surveying

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Bathymetry (Water Depth)

Bathymetry of Blacksod Bay (Click image for more detailed map).

In general terms, the bathymetry of the area is as expected with relatively shallow areas within the bays which deepen moving offshore. Water depths range from 0 metres to 140 metres offshore.

For a more detailed chart of the bathymetry of Blacksod Bay click here

You can download Bathymetry xyz data from IWDDS

(Data Type: Vector Datasets, Region: Offshore, Theme: Bathymetry (Survey Leg) entire survey leg or Bathymetry (Survey Line) for individual tracklines. Take note of the survey names in INFOMAR Survey History.

You can also download the bathymetry data in ArcGIS GRID format

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Shaded Relief

The 3D appearance is achieved using software called Fledermaus. By using some vertical exaggeration, artificial sun-shading (usually as if there is a light source in the nw 315°) and colouring the depths using various colour maps, it is possible to highlight the subtle relief of the seabed. This helps us to quickly understand the variation in depths.

Click image for more detailed map.

Detail of multibeam sonar data collected south of Duvillaun More off the SW tip of the Mullet Peninsula showing outcropping bedrock with sediment accumulation in the eastern lee side of the outcrop.

Detail of multibeam sonar data collected North of Slievemore, Achill Island showing sedimentary bedforms on the seabed.

All of our Charts for Blacksod can be downloaded in pdf format from this page.

Download Shaded Relief Bathymetry Geotiffs from our Interactive Web Data Delivery System (IWDDS)

Select your area of interest.Offshore Geotiffs - Bathymetry Shaded Relief Geotiffs. Take note of the survey names in INFOMAR Survey History.

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Backscatter

Multibeam Systems also collect additional information, including the strength of the acoustic signal (or return) from the seafloor. This is known as Backscatter. Differing seafloor types, such as mud, sand, gravel and rock will have different Backscatter values depending on the amount of energy they return to the sonar head. Rocky areas will typically have high returns while soft sediments like mud are more likely to absorb energy and have low Backscatter returns. These differing values are used to generate a grey-order image (i.e. dark for high returns, bright for low returns) of the seabed which can be used to examine the nature of the seafloor.

Click image for more detailed map.

Detailed .pdf backscatter charts can be downloaded by clicking here

Download Backscatter Geotiffs from our Interactive Web Data Delivery System (IWDDS)

Select your area of interest.Offshore Geotiffs - Backscatter Geotiffs. Take note of the survey names in INFOMAR Survey History.

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Ground Truthing/Seabed Sampling

To verify the results of remotely sensed sonar data, it is important to collect physical sediment samples from the seabed. These may be from the surface where grabs are used or may penetrate through the seabed and retain the vertical structure of the sediment by using various coring methods. These samples are also critical for the confirming seabed classifications.

The RV Keary took 23 grab samples (red circles)in Blacksod Bay in 2014. Almost half the samples were sand. The majority of the others were shell hash or shelly sand. Full Particle Size Analysis (PSA) was carried out on the samples. 44 samples (yellow triangles) were taken in Blacksod Bay in 2009 by the Marine Institute. Most of the samples were Sand & Gravelly Sand. 3 of the samples also had some mud. Full PSA was carried out on the samples. Offshore sampling (64) was taken using a vibrocorer in 2010 by the Celtic Voyager (blue circles). Geotechnical only with no PSA carried out.

Click image for more detailed map.

Sample locations can be downloaded as a shapefile from our Interactive Web Data Delivery System (IWDDS).

On the IWDDS Select your area of interest. Vector datasets - Offshore - Offshore Shapefiles

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Geology

Blacksod Bay Geology
The geology of the coastline surrounding Blacksod Bay is composed of very ancient, deformed rocks.

Some of these comprise a group of rocks called the Dalradian, which can be found in north Connemara and Donegal as well. Other packages of rock, such as the Inishkea Division and Mullet Gneiss, are even older still. Gneiss is a deformed version of granite and so is a metamorphic rock.

These rocks are heavily faulted and perhaps some of these structures can be traced offshore using the INFOMAR seabed data. Geologically, it is a very complex area.

Onshore Bedrock Geology shapefiles can be downloaded from our Interactive Web Data Delivery System (IWDDS).

On the IWDDS Select your area of interest. Vector datasets - Onshore - Bedrock

Offshore Geology shapefiles can be downloaded from our Interactive Web Data Delivery System (IWDDS).

On the IWDDS Select your area of interest. Vector datasets - Offshore - Offshore Shapefiles

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INFOMAR in Google Earth

To view and navigate around the Lidar 2008 Blacksod Bay dataset in Google Earth, click here

Image of Lidar data for Blacksod Bay in Google

To view additional datasets in Google Earth please click here

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Follow these links to your area of interest on the INFOMAR website:

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