Ogof Hesp Alyn facts for kids

Ogof Hesp Alyn is an exciting cave located in the Alyn Gorge near Cilcain, Flintshire, Wales. Its name means Dry Alyn Cave in Welsh. This amazing underground world was first explored by the North Wales Caving Club in 1973. Getting to the very end of this cave is a big adventure! It involves going down many drops and passing through underwater sections.

Exploring Ogof Hesp Alyn

Reaching the deepest parts of Ogof Hesp Alyn is a real challenge. Cavers need to navigate 24 "pitches," which are like vertical drops or shafts. They also need to get past two "sumps," which are parts of the cave passage completely filled with water.

How Cavers Get Around

In the past, cavers used wire ladders to get down the many drops. However, in the 1980s, a team of divers from the Wessex Caving Club explored beyond the sumps. They found that using a "single rope technique" (SRT) was much better. SRT means cavers use one rope to go up and down, which is easier than carrying lots of ladders.

To help keep the water levels low in the first sump, a special device called a "perpetual siphon" is sometimes used. This helps drain some of the water, making it easier for cavers to get through.

Mapping the Cave

The North Wales Caving Club created a detailed map of the cave. This map, called a "BCRA grade 5b survey," shows all the passages and features. They made parts of the map during the first explorations in the 1970s. Later, they added more details after exploring beyond the sumps in the 1980s.

Inside the Cave

Ogof Hesp Alyn has a main passage that twists and turns. But there are also several cool side passages to explore. These include:

• The Northeast Chambers
• The Mousetrap series
• The Wormway, which got its name because of the many worms living in its muddy areas!

Much of the cave is wet and muddy, right from the start. So, cavers need to be ready for a damp and dirty adventure!

How the Cave Formed

The cave passages stretch for about 2 kilometres (1.2 mi) and go down about 90 metres (300 ft) from top to bottom. Originally, the entrance to Ogof Hesp Alyn was a "rising." This means water used to flow out of the cave. However, in the early 1900s, mining operations lowered the water levels in the area.

Because of this, Ogof Hesp Alyn is special. It's a great place to study how caves form mostly from "phreatic processes." This means the cave was carved out by water completely filling the passages, deep underground. It hasn't been changed much by "vadose streams," which are streams that flow through air-filled passages closer to the surface.

Safety in the Cave

Even though the water levels are generally lower now due to the "Milwr Tunnel" (a drainage tunnel hundreds of feet below), the cave can still fill up completely with water during very heavy rain. This doesn't happen often, but anyone visiting the cave must be careful and aware of the weather. Even after the water goes down, one section called the "Sand Crawl" can stay flooded for weeks.

Nearby Caves

Ogof Hesp Alyn is close to another cave called Ogof Hen Ffynhonnau. This cave is about 150 metres (160 yd) further upstream in the Alyn Gorge. These two caves, along with Ogof Nadolig, are part of a special protected area. This area is called the Alyn Valley Woods and Alyn Gorge Caves SSSI. This means the area is important for its natural features and wildlife.