Weathering and Limestone Landscapes

Weathering of Limestone

1. Carbonic and Humic acids trickle along the joints of limestone widening them through the weathering processes of carbonation and solution.
2. Rates of weathering are increased by acid rain (enhanced by increased pollutants in the atmosphere - for example increases in carbon dioxide, increase concentrations of carbonic acid when mixed with rainwater)
3. In winter, frost shattering further weathers the limestone.

This page will focus on the Yorkshire Dales (see map above) as a case study of weathering of a limestone landscape.

Surface Features of Limestone Weathering

The following photographs show good examples of the main features of a limestone landscape created by weathering. For an account of the formation of these features view the pointpoint shown in class (see below photographs to download the pdf containing these powerpoint slides)

Many thanks to Val Vannet (Dundee High School) for the above photographs.

How do these features form?

Download the Limestone Weathering Powerpoint from class as a pdf file (this requires Adobe Acrobat Reader to view and print) - includes an overview of the main limestone landscape features with a focus on the Yorkshire Limestone of Malham and Ingleborough as case studies (many thanks to Val Vannet (Dundee High School) for the use of some of her fantastic photographs for this).

See also this excellent site from BBC Scotland Educational on Limestone in an Upland Area (Case Study based on Yorkshire Dales / Malham) - for more good links - see the bottom of this page.

Example Answer:

With reference to a named limestone area you have studied, outline the impact of weathering on the landscape. You may use a diagram to help your answer. (Jan 2002 Qu 2c)

Name area: Malham, North Yorkshire

In Malham there are extensive areas of carboniferous limestone which are easily weathered. The main weathering process is by carbonation in which rain (which is a weak form of carbonic acid) reacts with the calcium carbonate in limestone and causes it to dissolve. The rain particularly attacks lines of weakness which are the joints and bedding planes found in carboniferous limestone. in exposed areas this results in the formation of limestone pavements e.g. Malham. Here the joints are widened by carbonation to form grikes while the blocks are called clints.

Most of the area has little vegetation, few trees and little soil but where plants do survive chelation occurs ie. the decaying plant matter produces organic acids making the percolating water more acidic causing more weathering.

There are few surface streams flowing over carboniferous limestone as it is pervious. However at Ingelborough, North Yorkshire, surface streams start on impermeable rock and then flow onto the limestone. They soon disappear however into enlarged joints or depressions known as swallow holes e.g. Gaping Gill where the stream drops 10m into a large underground cavern.

In winter time frost action in the limestone joints is common e.g Malham Cove

See also the following links / resources...

Pictures of limestone features at Malham (Yorkshire) from the GeoBytes GeoPhotographs Gallery.

Limestone Weathering of the Malham Area (external site)

If you are stuck on any of these key concepts or want to develop your understanding further, try out some of the link from the Earth Systems Weblinks section.

See the Limestone links on the excellent Geography Pages.

For some more summary notes and some excellent weblinks see also the Weathering section on Geography Pages (with thanks to Alan Parkinson from King Edward VII School, Kings Lynn).