Mapping Mountains – Significant Height Revisions – The Fours – The 400m Hills of England

 

Belles Knott (NY 297 085) 

There has been a Significant Height Revision to a hill that is listed in the The Fours – The 400m Hills of England, with the summit height, col height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Belles Knott (NY 297 085)

The criteria for the list that this height revision applies to are:

The Fours – The 400m Hills of England - English hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list is a sub list entitled the Sub-Fours, the criteria for which are all English hills at or above 400m and below 500m in height that have 15m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available to download in Google Doc format from the Mapping Mountains site.

The Fours - The 400m Hills of England by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Belles Knott, and it is adjoined to the High Raise group of hills, which are situated in the Lake District, and it is positioned with the B5343 road to its south and the A591 road to its east, and has the village of Grasmere towards the east.

When the Introduction to the first group of hills for the updated and revised listing of the The Fours – The 400m Hills of England was published by Mapping Mountains on the 10^th September 2022, it was announced that the accompanying sub lists were being revised with the two 390m categories dispensed with and the criteria and name of the 400m Sub-Fours revised.  The one accompanying sub list is now named the Sub-Fours with its criteria being all English hills 400m and above and below 500m in height that have 15m and more and below 30m of drop.

Prior to this revision this hill was listed with an estimated c 21m of drop, based on an estimated c 493m summit height and an estimated c 472m col height, with both heights based on interpolation of 5m contouring that appeared on the interactive mapping hosted on the OS Maps website. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Belles Knott (NY 297 085)

LIDAR analysis gives the height of this hill as 490.6m positioned at NY 29711 08585, and when compared to its originally listed summit height this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 490.6m and this was derived from LIDAR analysis, this is 2.4m lower than the originally listed c 493m summit height, which was based on interpolation of 5m contouring that appeared on the interactive mapping hosted on the OS Maps website. 

 

The full details for the hill are:

Group:  High Raise

Name:  Belles Knott

OS 1:50,000 map:  89, 90

Summit Height (New Height):  490.6m (LIDAR)

Summit Grid Reference:  NY 29711 08585 (LIDAR)

Col Height:  471.65m (LIDAR)

Col Grid Reference:  NY 29595 08661 (LIDAR)

Drop:  18.9m (LIDAR)

 

Myrddyn Phillips and Aled Williams (February 2025)