(Image by Matthew Pinner)
Just as the Red Sandstone of the Triassic is an enigmatic feature of the Jurassic Coast’s most westerly gateway in East Devon. So is the dramatic white Cretaceous chalk cliffs and stacks on the most easterly edge of this UNESCO World Heritage Site known as Old Harry’s Rocks on the Isle of Purbeck by Handfast Point.
Until 1896 Old Harry was joined by another chalk stack called "Old Harry’s Wife" until erosion by the sea saw her fall leaving him widowed to stand alone on an outcrop known as "No Man’s Land". The reference to Old Harry has many origins including being named after the Devil who apparently slept on the rocks or a Poole pirate called Harry Paye or 'Arripaye' by the French and Spanish from whom he plundered on the high seas throughout the late 14th and early 15th century.
Old Harry’s Rocks are viewable along the South West Coast Path from Studland or from Swanage joining the Purbeck Way near Ballard Point and walking along Old Nick’s Ground. Both of these paths cross Ballard Down managed by the National Trust. Ballard Down is a chalk grassland that covers the headland and is awash in Spring and Summer with a diverse array of calcareous-loving wildflowers and grasses
(Image by Matthew Pinner)
This part of Dorset has chalk dating back 80 – 100 million years to the Cretaceous (meaning “Chalk”) and is among the youngest rocks of the Jurassic Coast. Chalk is almost pure limestone (calcium carbonate) formed in warm marine environments by the shells of microscopic marine algae known as coccoliths. As this algae died, their skeletons would sink to the sea bed and over time a thick, often very thick, a soft ooze of coccoliths was compacted and hardened creating chalk.
This headland promontory has a wonderful topography or arrangement of natural landscape features including sea stacks, natural arches and of course vertical cliffs that are potentially dangerous so stay back from the edge.
Old Harry Rocks has been formed by continuous coastal headland erosion since the end of the last ice age known as the Devensian 12,000 years ago. Old Harry once formed the chalk promontory of Handfast Point and whose chalk ridge-line would have extended as far as The Needles on the Isle of Wight.
In considering how a stack is formed I can’t help but think of the quote by Geoffrey Chaucer in his prologue to the Clerk’s Tale, “Time and tide wait for no man”. Though this quote from 1395 was more to do with people procrastinating about voting it is also comparable in certain respects to the relentless impact of erosion and how it cannot be stopped by the passage of time.
Old Harry's Rock started to form when the faults or lines of weakness within the chalk rock were attacked by the hydraulic action, abrasion and chemical erosion of both the sea water and rain. Over time these faults grew from small caves into a much larger, deeper and wider cave until it breached the headland forming an arch. As a natural feature an arch has no keystone allowing the arch to bear weight so as the erosion continued the arch would have gradually become unsupported until it eventually collapsed leaving a stack.
If you are visiting Dorset it is recommended you take the walk from either Studland or Swanage up to the headland to see Old Harry Rocks. Its a spectacular view and not an easily forgotten feature of the Jurassic Coast.