The origin of Dulwich Hill

[edhistory]

> Re: Tree scuplture junction of East Dulwich Road and Peckham Rye

> Posted by hornbeam September 15, 11:32AM

>

> Well, I'm pleased my blog post of a couple of years ago was helpful -

> [thetreesaroundnunhead.blogspot.co.uk]

> Someone mentioned a 'surprising' origin for Dulwich Hill. I'd love to know more...

> Graham

Sorry for the delay, I was trying to find a suitable map that has hatchings for the sides of Dulwich Hill.

This is Stanford's Pocket London Map from 1861.

By this time the property speculators had fragmented the Dulwich Hill name into Champion Hill and Denmark Hill.

Dulwich Hill has an odd shape running from Warwick Gardens in the east to the Effra Gap at Herne Hill.

The question is how Dulwich Hill got to be there. What geomorphological made it?

John K

[Ruskin]

This has always fascinated me as we live on the northern end of the escarpment and over the years we've been here, cycling and more latterly, running up and down the slopes has got me wondering the same thing.

Without any true knowledge though, I would have personally thought it was a natural peak but are you suggesting that because of its height above the Thames valley, it might have been formed in antiquity?

What about a Hill Fort? A lovely thought!

And delighted to see the Myatts Fields market gardens still present, top left.

[Townleygreen]

Ruskin, it is definitely a natural hill! No doubts exist on that point.

The "usual" reason for a hill in this sort of location is that it is one or more of the following:

1 consists of more resistant rock than its surroundings, so erodes more slowly = higher

2 if its no more resistant than its surroundings, then it may have been protected by a cap of more resistant materials in the past, slowing down its erosion

3 rivers may have followed easier routes which took them around the hill, leaving it relatively higher as they eroded the lower land surrounding the hill

4 it may be a geological formation whose structure makes it less easy to erode

I am not sure which particular explanation is the one in this case.

[KidKruger]

...or it could be a volcano.

Dulwich Volcano.

Now that sounds pretty cool, don't it ?

[MarkE]

A borehole scan at the top of the hill, from the Geo Survey website... http://mapapps.bgs.ac.uk/geologyofbritain/home.html?mode=boreholes

If you look carefully you can see the tippex over the top of the bit that originally said "molten lava"...

 

[edhistory]

KidKruger Wrote:

-------------------------------------------------------

> ...or it could be a volcano.

>

> Dulwich Volcano.

>

> Now that sounds pretty cool, don't it ?

Well, East Dulwich does has its very own earthquake fault line.

The Thames Water engineers doing the geological survery were pretty sure it runs under St Barnabus Church and then heads off towards Honor Oak, but not crossing the line of the water tunnel they were boring.

John K

[edhistory]

Townleygreen Wrote:

-------------------------------------------------------

> Ruskin, it is definitely a natural hill! No doubts

> exist on that point.

>

> The "usual" reason for a hill in this sort of

> location is that it is one or more of the

> following:

> 1 consists of more resistant rock than its

> surroundings, so erodes more slowly = higher

> 2 if its no more resistant than its surroundings,

> then it may have been protected by a cap of more

> resistant materials in the past, slowing down its

> erosion

> 3 rivers may have followed easier routes which

> took them around the hill, leaving it relatively

> higher as they eroded the lower land surrounding

> the hill

> 4 it may be a geological formation whose structure

> makes it less easy to erode

>

> I am not sure which particular explanation is the

> one in this case.

A futher one, which at first seems so unlikley:

5. River valley capture.

John K

[Ruskin]

A few years ago we questioned our building insurers who had almost doubled our premium stating we were at risk from subsidence due firstly to 'earthworks'.

I know there were allotments in the park during the war but that seemed ridiculous at the time but are these referring to the 0-10m bore holes shown in the area?

Also, I see that this area is peppered with boreholes - some of which are black meaning (according to the key) these are 'confidential or restricted.' Can you explain why they're there and why they'd be restricted?

[Townleygreen]

>>>>John K wondered:

>>>>A futher one, which at first seems so unlikley: 5. River valley capture.

I don't think that is relevant to the hill - it doesn't explain why there is a hill there. It would only influence the SHAPE of that hill.

[edhistory]

That's what I thought until I applied a 2 metre resolution LiDAR dataset to the problem.

I ran the GIS mapping from Herne Hill, through North Dulwich, East Dulwich and on to Peckham.

The result is a very different landscape history for the western East Dulwich valley.

There's quite a lot of background detail to this which I will try to condense to bullet points and post here at the weekend.

JOhn K

[edhistory]

Dulwich Hill is a "free-standing" shoulder of land.

What erosion/weathering process(es) created it?

The first map is from Herring's London Sewer Map of 1882. This is useful because the contours are clearly shown as the road and housing clutter is excluded.

It is clear from this map that Dulwich Hill is the western bound of the Nunhead and East Dulwich Valley.

The shoulder of land is broken at Herne Hill but then continues southward across Brockwell Park.

The second map was produced in ArcGIS using a 2 metre resolution LiDAR dataset. The standard ArcGIS contour shading tool was applied consistently across the map and tweaked until the Effra watershed between Gilkes Crescent and Great Spilmans disappeared. This also closed the Herne Hill Gap.

The third map is from the Ordnance Survey County Series. The 75 foot contour marked in red shows the large dried up river bed. If the Effra did flow through East Dulwich, then that's how the water got out of the valley into the Peckham Marsh.

I have more information if anyone wants to drop by and talk about it.

John K

[nashoi]

Isn't the most likely answer glacial erosion during the last ice age, when the thames changed to its current course. Geological maps of the borough show an outcrop of different rock.

[Townleygreen]

no glaciers ever reached South of Finchley in the last ice age

[nashoi]

Ah, true enough Townleygreen, might have known not even glaciers would come south of the river.

[edhistory]

http://www.essexfieldclub.org.uk/portal/p/Geology+Site+Account/s/Hornchurch+Railway+Cutting+SSSI/o/Hornchurch+Railway+Cutting+SSSI

I've been meaning to visit Hornchurch, but I don't have a visa for north of the river.

John K