Tylorstown landslip, 2020

On 16 February 2020, during Storm Dennis, the upper of two former colliery spoil heaps on the Llanwonno hillside above Tylorstown, in the Rhondda Fach, failed and flowed into the valley below; no one was hurt.

Cause

Extreme rainfall from Storm Dennis, described as a one-in-two-hundred-year storm, saturated a Category D colliery spoil tip; the upper heap failed as a rotational slip that broke down into flows reaching the river.

What happened

About sixty thousand tonnes of coal-waste spoil moved down the Llanwonno hillside during Storm Dennis, one of three storms in quick succession, when Maerdy at the head of the valley recorded the highest rainfall in Wales. The failure began, on Dave Petley's reading for the AGU Landslide Blog, in the upper of the two spoil heaps as a rotational slip, the lower part of the block fragmenting into flows that reached and inundated the Rhondda Fach. The slide blocked the river valley, broke a foul sewer, buried a strategic water main and covered a footpath and cycle path; the area was closed to the public at once. Rhondda Cynon Taf council then carried out a four-phase remediation, removing the spoil and stabilising the remaining tip over the following years. The failure drew fresh attention to the safety of the disused coal tips of the South Wales valleys.

This account describes a post-closure incident in abandoned workings. It is not an access guide, and deliberately omits route detail beyond what's needed to understand what happened.

Sources

1. (primary) Tylorstown Landslip remediation process — Rhondda Cynon Taf County Borough Council
2. (secondary) Did South Wales suffer a coal waste landslide yesterday? (17 February 2020) — The Landslide Blog, AGU (Dave Petley)

Record created: 16 September 2026 · Last researched: 22 September 2026