From the top of Scrabo hill, you have an unparalleled view of the long, narrow hills all around, rising about three metres high and 300 metres in length, with one end higher than the other. These are ‘drumlins’, parallel formations found in their thousands across Northern Ireland, which were left behind by glaciers 13,000 years ago.
Drumlins can be found all over the world, however, the word was originally coined by the Irish from the Gaelic word druim for ‘ridge’ or ‘hill’. Drumlin became a worldwide geological term in the 1800s, following the work of Irish geologists Maxwell Henry Close and George Kinahan, who determined the flow of the disappeared ice sheet from the drumlins’ tear-drop-shapes. Like much of Ireland, this region was under an ice sheet up to one kilometre deep.
From the Scrabo vantage point, you see how all the drumlins point west to east, with their lower end facing the direction the ice was going. They appear to be tumbling like an earthy current towards the water of Strangford Lough, where more drumlins have created a group of tiny islands. Their undulating shapes give the illusion of movement, like a shoal of slow, green sea creatures. These ‘drowned’ drumlins would have been formed on land, but since the last Ice Age the water has risen up to meet them.
An explanation for drumlins still eludes scientists. Even where there are existing glaciers, the transformation occurs under the ice, hidden from view until the glacier recedes. Two main theories have battled over their origins: the first, that they are made from accumulated sediment, or ‘till’ off-loaded by the glacier. The second, that they were carved out of the ground by the movement of ice across the land. The problem is the sheer variety of drumlins in nature: there are some made with layered till, others with a core of bedrock, and some made entirely of bedrock. A sound theory would need to consolidate all of their mutations.
An answer could come from climate change. As many glaciers recede due to rising temperatures, some of them reveal newer drumlins as they go. In 2010, Iceland’s Múlajökull glacier became famous to geologists as warmer climate reduced it enough to expose an active drumlin field. With similar events expected to occur in Antarctica, it could be that the processes behind landscapes like Strangford Lough are finally understood. For now, its mysteries enhance it.
This was published in the July 2017 edition of Geographical magazine.