You'll be blubbing over a wooden boulder at David Nash's show at Towner Art Gallery

Call me soppy, but when the credits rolled on ‘Wooden Boulder’, a film made by earth artist David Nash over 25 years, I was blinking back tears. Funny what the mind will make human. Within a few minutes I started to think of Nash’s boulder, hewn from a storm-struck oak in the Ffestiniog valley in Wales, as ‘the hero of our story’. A hefty hero, weighing half a tonne, but buoyant.

In October 1978, Nash launched the boulder into the Bronturnor stream near his studio at Capel Rhiw in the slate-mining village of Blaenau Ffestiniog in Snowdonia. For 25 years, switching from crackling film to high-def digital, Nash filmed the boulder, through snow, rain, heat and gloom of night, as it made its way downstream. Mired, moored, marooned on an inland sea. Submerged, beached and bowling along. Stuck, stuck, stuck in the mud. ‘Free-range sculpture’, Nash, now 73, calls it. Sometimes the boulder bobs, sometimes it sulks, sunken up to its eyeline like a crocodile. In summer, the wood cracks; in winter, the boulder is tonsured with sleet. Years accumulate. The boulder lurks like a troll under a bridge and has to be levered free. God, what a ravishing country, you think, as our Odysseus, our Wandering Jew, our knight-errant, passes waterfalls, hills, washes and marshes. In August 2015, heavy rains and high tides swept the boulder away. Nash has searched high and low, checked every creek, ditch and bulrush. He has flown drones over deep water. ‘It has never been seen since,’ reads the video text. ‘It is somewhere.’ Sniffle, sniffle.