Panshanger Park is 1,000 acres of countryside situated between Welwyn Garden City and Hertford. Herts and Middlesex Wildlife Trust is working with the park's owners, Tarmac, to manage the park for both people and wildlife. Jo Whitaker explains the geology of Panshanger Park.

Welwyn Hatfield Times: The River Mimram flowing through Panshanger Park is a chalk river.The River Mimram flowing through Panshanger Park is a chalk river. (Image: Jo Whitaker)

As you’re walking around Panshanger Park you may be enjoying seeing the wide variety of wildlife that calls it home.

You may also be interested in the heritage of the site, seeing relics of it such as the Orangery and the remains of the house. What you may not have considered is the slightly more hidden aspect of the park, the rocks.

The predominant rock under the ground at Panshanger Park, known as bedrock, is chalk. Chalk is a porous rock and is common in the South East of England. Chalk was originally formed when the land was under a warm, clear sea millions of years ago.

Chalk forms some of the features such as the chalk river, the River Mimram, flowing through the centre of the valley. The porous chalk beneath the ground in this area of the country stores water like a large, albeit non-squishy, sponge - this is known as an aquifer. As well as being the source of water for some of our chalk rivers, they also supply our drinking water.

However, the chalk is only close to the surface in the valley bottom of the park. On the slopes of the valley, there is gravel and unsorted rock deposits, meaning the rock is made up of lots of different sized sediments.

About half a million years ago the River Thames flowed through Panshanger, so some of these rocks, such as flint pebbles, were deposited by the river. You may see some of these flint pebbles along field edges when you’re walking around the park. The more unsorted rocks, known as till, were actually left by glaciers during the last glaciation about half a million years ago!

Some of the gravel has been quarried at Panshanger to be used for building, housing and roads. The large lakes at Panshanger are gravel pits, meaning they were left to fill with water after the quarrying, creating excellent habitats for wildlife.

The quarrying has now finished and the area has been restored back to the parkland and nature reserve you see today.

So, when you’re next out on a walk around the park, you now know what’s beneath your feet!

If you’d like to learn more about the geology of Panshanger Park then join us at our upcoming guided walk on February 21. More information and booking details at

Welwyn Hatfield Times: Jo Whitaker, Panshanger Park People & Wildlife OfficerJo Whitaker, Panshanger Park People & Wildlife Officer (Image: Jo Whitaker)

Jo Whitaker is the Panshanger Park People and Wildlife Officer. She works for Herts and Middlesex Wildlife Trust and her role is funded by Tarmac.