Soil colors – what more could you want?

Nuno Simões
University of Algarve, Portugal

Nuno Simões (before combing). Meet Nuno at EGU2014-SSS2.7.

We can easily see that soil color varies from one site to another, with depth, with topographic position and composition. Even color may be light brown in one side of the road and dark brown in the other. Whether for scientific purposes, or just curious, you study the colorimetric interesting variations.

Why does soil color change?

The soil color varies due to the characteristics of substances that form it. These variations can be caused by several factors, as, for example, soil humidity (the wetter the soil is, the darker it gets), soluble salts, sand and carbonates (light colors), iron oxides (red colors), organic matter (dark colors), etc.

How can soil color be measured?

Soil color is usually described using the Munsell color scale, which is a very good tool for soil taxonomy, for example. But there are other interesting methods that can be used depending in our purposes. The method I am presenting here uses the ColortronTM spectrophotometer, a device that measures the color at the surface of solids and transfers it to the ColorshopTM program. This spectrophotometer can use various color scales such as CIE Lab, CIE RGB, CIE XYZ, among other scales.

A study case

This example is a study conducted in Boca do Rio (Algarve, southwestern Portugal), which consisted of the identification of sedimentary deposits of the 1755 tsunami in the area. We used the CIE Lab color model which, according Nederbragt and Thurow (2004), is the most suitable for paleoenvironmental studies. CIE Lab aims to mimic the way the human eye understands the color and is divided into three parameters, L*, a* and b*. This color space is organized in a three-dimensional model, where L* is the vertical axis and is defined by lightness (Figure 1). The maximum brightness is L* = 100, which represents a perfect diffuser (reflecting white) and the minimum is 0, which represents black. Value of L* is conditioned by organic matter and carbonate contents (Helmke et al., 2002), as well as water content. In contrast, a* and b* represent the chromaticity and do not show numerical limits. The value of a* is positive when it tends towards red, and negative when it tends towards green. Similarly, b* is positive when it tends to yellow and negative when it tends to blue.

Figure 1. CIE Lab scale.
Figure 1. CIE Lab scale.

How to?

Usually, three replicated color measurements are carried out with the Colortron and average values are used as representative.

Figure 2. Sediment sampling.
Figure 2. Sediment sampling.
Figure 3. Sediment samples prepared to start measuring (left) and Colotron device (right).
Figure 3. Sediment samples prepared to start measuring (left) and Colotron device (right).

After obtaining and processing data (Figures 2 and 3), results can be plotted to obtain brightness and chromaticity graphics (Figure 4).

Figure 4. Brightness (CIE L) and blue-to-yellow chromacity (CIE b) from bulk sediment and siliciclastic fractions (Font et al., 2013).
Figure 4. Brightness (CIE L) and blue-to-yellow chromacity (CIE b) from bulk sediment and siliciclastic fractions (Font et al., 2013).

Figure 5 show the relation between b* value of the siliciclastic fraction and the average particle size. Relations between data obtained at the base of the deposit and the C unit and at the top with A unit were found. Note that the tsunami deposit layer is located between the units A and C.

Figure 5. Relation between average particle size (mean AS) of siliciclastic fraction and parameter b* (Font et al., 2013).
Figure 5. Relation between average particle size (mean AS) of siliciclastic fraction and parameter b* (Font et al., 2013).

Another way to confirm these results is to use the obtained values as a scale for an image editor, in this case, the CIE Lab color model. Thus it is possible to build a profile with the color corresponding to the sampled places (Figure. 6).

Figure 6. Color of a portion of an horizontal profile of the Arrifes beach, southern Portugal.
Figure 6. Color of a portion of an horizontal profile of the Arrifes beach, southern Portugal.


I want to thank Cristina Veiga-Pires and Eric Font for their help with the identification of tsunami deposits in southern Portugal.


Font, E., Veiga-Pires. C.C., Pozo, M., Nave, S., Costas, S., Ruiz Muñoz, F., Abad, M., Simões, N., Duarte S. 2013. Benchmarks and sedimentary source(s) of the 1755 Lisbon Tsunami deposit at Boca do Rio estuary. Marine Geology 343;1-14. DOI: 10.1016/j.margeo.2013.06.008.

Helmke, J.P., Schulf, M., Bauch, H.A. 2002. Sediment color record from the Northeast Atlantic reveals patterns of millenial-scale climate variability durin the past 500 000 years. Quaternary Research 57: 49-57. DOI: 10.1006/qres.2001.2289.

Nederbragt, A.J. Thurow, J.W. 2004. Digital sediment colour analysis as a method to obtain high resolution climate proxys records. In Francus, P. (Ed.), Image Analysis, Sediments and Paleoenvironments. Developments in Paleoenvironmental Research, Vol. 7, Chapter 3. Kluwer Academic Publishers. Pp. 105-124. DOI: 10.1007/1-4020-2122-4_6.


This post has been published simultaneously in the EGU Blog Network.


Monday paper: Paleosols in the Transantarctic Mountains: indicators of environmental change

Bockheim, J. G. 2013. Paleosols in the Transantarctic Mountains: indicators of environmental change. Solid Earth 4, 451-459. DOI: 10.5194/se-4-451-2013


The Transantarctic Mountains (TAMs), a 3500 km long chain that subdivides East Antarctica from West Antarctica, are important for reconstructing the tectonic, glacial, and climatic history of Antarctica. With an ice-free area of 24 200 km2 (50% of the total in Antarctica), the TAMs contain an unusually high proportion of paleosols, including relict and buried soils. The unconsolidated paleosols range from late Quaternary to Miocene in age, the semi-consolidated paleosols are of early Miocene to Oligocene age, and the consolidated paleosols are of Paleozoic age. Paleosols on unconsolidated deposits are emphasized in this study. Examples are given from the McMurdo Dry Valleys (78° S) and two outlet glaciers in the central and southern TAMS, including the Hatherton–Darwin Glacier region (80° S) and the Beardmore Glacier region (85°30′ S). Relict soils constitute 73% of all of the soils examined; 10% of the soils featured burials. About 26% of the soils examined are from the last glaciation (< 117 ka) and have not undergone any apparent change in climate. As an example, paleosols comprise 65% of a mapped portion of central Wright Valley. Paleosols in the TAMs feature recycled ventifacts and buried glacial ice in excess of 8 Ma in age, and volcanic ash of Pliocene to Miocene age has buried some soils. Relict soils are more strongly developed than nearby modern soils and often are dry-frozen and feature sand-wedge casts when ice-cemented permafrost is present. The preservation of paleosols in the TAMs can be attributed to cold-based glaciers that are able to override landscapes while causing minimal disturbance.

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Solid Earth (SE) is an international scientific journal dedicated to the publication and discussion of multidisciplinary research on the composition, structure and dynamics of the Earth from the surface to the deep interior at all spatial and temporal scales. More at Solid Earth hompage.

Soils at Imaggeo: ‘Lithic Rhodoxeralf’, by Jorge Mataix-Solera

This soil profile is a Lithic Rhodoxeralf (Soil taxonomy), Chromic Luvisol (World Reference Base for Soil Resources), commonly called Terra rossa. The picture was shot in Located in Alicante (SE Spain).

Click the picture for more information, contact data and full resolution.

Lithic Rhodoxeralf, by Jorge Mataix-Solera. Click to see the original picture at Imaggeo.

Imaggeo is the online open access geosciences image repository of the European Geosciences Union.

Photography as a tool for teaching support in geosciences. An example for soil sciences: the colour of the age

Jorge Mataix-Solera
GEA – Grupo de Edafología Ambiental
Departamento de Agroquímica y Medio Ambiente. Universidad Miguel Hernández, Elche, Alicante, Spain

Teaching in geoscience currently is easier than decades ago. Lots of tools can support the lectures in the classrooms, such as innovative teaching web pages, portfolios, social networks pages, etc. All of this can help teachers to do explain geodynamic processes. Pictures with short descriptions are very useful for teaching. An example for soil science is this one, this set of four pictures of different soil profiles that won the European Journal of Soil Science Photocompetition 2011 (figure 1).

Typic Calcixeroll. Sierra de Aitana, Alicante, Spain.
Figure 1. The color of the age.

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