Every feature of the Irish landscape bears a distinctive name. Altan is a Gaelic word for a steep glacial trough, left over from the last Ice Age. Northwest County Don-egal is furrowed with altans, often in the form of elongated mountain lakes. Loch Altan stands deep and silent at the foot of Aghla More, near stony Mackoght and mighty Mount Errigal, tallest in the Derryveagh range. Altan, one of Ireland’s longest-running and best beloved folk bands, cites this region and Loch Altan in particular as the source and inspiration for its music.

Altan’s cofounder Mairead Ni Mhaonaigh (pronounced Maw-RAYDT-nyee-WAY-nee) grew up in Atlantic coastal Gweedore, within sight of Errigal. Traditional Irish music was part of her upbringing. Whenever she gets hold of a fiddle, her face takes on a no-nonsense grin. It’s the smile of her father, who taught her the art of Donegal-style fiddling, and of her grandmother, from whom he learned it when he was young. Grinning at her bandmates, she plies the bow over the strings, setting up a jig that soon becomes a reel and then a feisty hornpipe.

Many years ago, an eighteen-year-old lad from Belfast named Frankie Kennedy was deeply impressed by young Mairead after hearing her fiddle and sing. Roundly smitten, he took up the tin whistle and resolved to acquire enough skill to perform along with her. A musically enhanced relationship blossomed; their courtship lasted six years, during which he set about mastering the Irish blackwood flute. They married, formed a band in the late 1980s, and named it after their favorite loch.

Kennedy is fondly remembered as a true gentleman with a rare sense of humor. His death at the age of thirty-eight devastated all who knew him. Last year in an interview with the Irish Examiner, his widow described how music helped her to plumb the depths of her own psyche in order to cope with the loss of her soulmate. Even while undergoing cancer treatments, he insisted that Altan continue to tour and record, and worked with the group for as long as he was able. His spirit is still very much at the heart of the sound of the band.

Mairead’s voice is disarmingly lovely, gentle and warm like golden sunshine, or wistful as midnight, moonlight, bells, and running water. An old-time slow air sung in the mother tongue can be comforting and reassuring. It doesn’t matter if you don’t speak the Irish language, explains Altan’s bouzoukist Ciaran Curran, because people pick up on the emotions being expressed rather than the actual words, “and that’s a very universal thing.”

Altan returns to the Ark for an evening of traditional Irish music on August 8.