Friday, 16 March 2018


Volume 6, Issue 4
October -  December 2017

Chair’s Foreward

In this issue we look at the use made in earth science teaching and research of virtual globe applications, in particular,  Google Earth. In 2013 Society of African Earth Scientists (SAES) set a challenge to use Google Earth to measure the land area and coastline of Africa as part of Day of Earth Sciences in Africa (DESA), held on 20-21st March each year. Five years later it will be interesting to revisit this activity and note if there have been any significant changes in results, particularly if we can note any change occurring in the length of the  African continental coastline in the last half-a-decade.

This year DESA is coinciding with the joint international congress of both the Arab Geosciences Union  and the African Association of Women in the Geosciences, entitled “ Earth Sciences for Society”, and hosted at Chouaib Doukkali University, Morocco, 20-24th March 2018.

In our publication review, a spotlight is put on soil erosion in Africa, where increasing scarcity of land is leading to farm cultivation on steeper and steeper sloped land, unsuited to farming because of the catastrophic soil erosion that can be brought about when steep slopes are used. On steep slopes, runoff acquires greater velocity and erosive power, to greatly increase soil erosion. We look at how vetiver grass technology can be used to arrest this problem. The science of erosion protection on slopes must guide a judicious use of the right  traditional farming methods on steep slopes, such as stone lines (provided slope steepness is not so steep as for stones or rocks to become   prone to rolling) or terracing, rather than, for instance, a tillage system of soil mounds that only leads to more serious erosion involving soil and nutrient loss. Soil mounds, which are well suited for flat land or gentle slopes, but which worsen erosion on steep slopes (as they encourage runoff concentration and gully erosion) are too often used  on steep slopes by farmers without awareness of the dangers. The need for  education of African farmers about soil and water conservation is therefore seen as essential and even  urgent. 

Collect Earth Mapathon Event in Gatsibo, Rwanda (via Fletcher, K., Woldemariam, T.,  and F. Stolle, "Scientists Use Google Earth and Crowdsourcing to Map Uncharted Forests", World Resources Institute, 2017)

Google Earth and other Satellite Applications as Earth Science Research and Education Tools

Google Earth (GE ) gathers data from various satellites orbiting our planet to gain information from space  on objects observed on the planet surface  to an accuracy as good as 0.5m width (20 inches).
   This time lapsed data can be employed to study our changing  environment including  such related problems as soil erosion, land degradation as well as  deforestation and desertification.
   GE represents a powerful tool with potential  for large savings in on-site survey costs, particularly in the rural areas of developing countries  which might otherwise be inaccessible. It is feasible that in the near future African engineers maintaining the Trans-African Highway will not need to travel to  locations were highways maintenance is needed to assess repair requirements. Rather, they will be able to access the information from virtual time lapsed images of the highway accessible from their office desk, using Google Earth (GE).
   GE is also of value in monitoring deforestation and desertification. According to Fletcher, Woldemariam and Stolle in a paper for the World Resources Institute, it takes huge effort to count the trees in a forest. However, using crowdsourcing scientists have recently been able to count the trees in the worlds drylands making up 40% of the earth’s land surface [1].
A great source of help in this exercise was the use of local people’s knowledge. Fletcher,et al report that this improved the accuracy of the count by about 9%. This is because local people were familiar with the types of vegetation and plant life to be found in the locality and from remote satellite images were able to distinguish for instance a shrub from a tree, or several trees from a forest. This local knowledge was contributed by means of local "mapathons", using google satellite technology to count and to map trees and forests. It enabled imagery from satellite observation to be checked against real data on the ground to ascertain the level of human error, and make the appropriate adjustment.
      Areas of earth science such as hydrology have also seen a great advantage in the use of Google Earth. There is a web-based hydrologic educational system called HydroViz that supports students learning in hydrology or related earth science subjects and serves as a virtual hydrologic observatory. [2]
   There are also papers published proving Google earth to be a potent conservation tool [3]. Many projects on the ground have taken off due to information gathered initially through use of Google earth and then later consolidated in the field. An example is the case of Julian Bayliss from Tanzania who conceived of and helped to lead a project of conservation in Tanzania that led to the discovery of new species, including 3 new species of butterfly and a new member of the poisonous Gabon viper family. The use of Google earth resulted in a virtual discovery that then led to an actual one.
   Google earth now offers the possibility of virtual field trips  for earth science students to any place on the planet. Today many countries are using satellite technology to monitor their environment, and Brazil is at the forefront. It uses the technology to track deforestation as it happens.
   Google Earth is also being used for original research: A study published in the Proceedings of the National Academy of Science recently was based on the analysis of 8,510 cattle spotted in google earth images[4]. Two-thirds of the cattle were found to align themselves with the earth’s magnetic field lines in a north- south direction. Thus the research employed satellite technology to prove a phenomenon that had been in plain sight for hundreds and thousands of years: that large non-migratory animals were affected by the earth’s magnetic field. Previously data had shown that migratory birds, fishes, butterflies and animals were guided by magnetism.

Online Geo-data Collection Activity hosted by Society of African Earth Scientists on 20th March 2018 as part of Day of Earth Sciences in Africa (DESA)

In 2013 SAES hosted a challenge to measure the coastline and land area of Africa using Google Earth. In 2018 this will be launched again for a second time by  the Society of African Earth Scientists (SAES) on the 20th – 21st March. The event will be an on-line geodata collection activity involving the measurement of the length of Africa’s coastline and the area of Africa’s landmass.  All participants are invited to post their results on the SAES facebook page on the 20th– 21st March or email their results.

Activity Summary
To measure the area and coastline of Africa’s landmass in square km and km respectively, using Google earth software. Google earth software is downloadable free from the Internet. 

The SAES hosted activity 
·         - encourages participants to become  familiar with a potential earth science tool that is freely  available
·         - enables appreciation of the true size of the African continent, until recently unknown.
Detailed Description of the Activity
The Society of African Earth Scientists’ Earth Science Day activity invites us to measure two quantities: the area and the coastline of the African continental landmass. The tool  recommended for this exercise is Google earth. Google earth can be freely downloaded from the internet, and measures distances on the surface of the earth. Google earth allows participants to measure Africa’s coastline very easily; whilst we needed to work harder to get an estimate of area.
    Ideally, we could get a very good estimate of Africa’s area by supposing that the shape of Africa is made up of an array of very thin rectangles of equal width, d, (see fig. 1).  The thinner the width, d, the more accurate is the estimate. Theoretically, if the width d is infinitely small, the estimate is exact [5]
   In practice, it is very time consuming to measure area by making the width, d, so fine as to require the use of many rectangles to fill up the shape of Africa approximately.
A quicker method which still gave an acceptable accuracy within 5% was to approximate the shape of the continent as closely as possible using an arrangement of rectangles and triangles to occupy the space inside the outline as closely as we see fit. We then determined the areas of these rectangles and triangles in the usual way (i.e., the area of a triangle is ½ x base xheight; whilst that of a rectangle is width x length), and we summed all the areas to obtain the estimate of the area of Africa’s landmass.

On-line Data Collection - Exemplary Results, 20th March 2013
i)      Measurement of the length of the African coastline.
A measurement using Google earth of 26,226 km was obtained (with an error of 0.87% from the true value of 26,000 km). Let us see if the results of the measurements we obtain in 2018 are substantially different.

ii)     Measurement of area of Africa’s landmass.
The exemplary results of measurements made are shown penned into the map of fig. 2 below. Summing up the areas of all the composite rectangles and triangles shown, gave an area of 29,040,169 km2 (an error of 3.9% from the true value of 30,221,532 km2). Whereas measurements of area have a level of error too high to enable meaningful comparison of land area now  with land area of 2013; coastal measurements are perhaps sufficiently accurate for these to be meaningfully compared. 

This is an area known to encompass the United States of America, Mexico, China, Japan, India, Iberian Peninsula, and Western Europe including the UK.

Earth Science Publication Review

United nations University Institute for Natural Resources in Africa, UsingVetitver Technology to Control Erosion and Improve Productivity in Slope Farming, Oku, E.E.., Aiyelari, E. A., Asubonteng, K. O.,  Accra, Ghana, 2015.[6]

Of the factors that affect the severity of soil erosion, slope is one of the most prominent. Some researchers have noted that runoff (overland flow of water) becomes a dominant agent of soil erosion on steep slopes [Kamalu 1994, Morgan 1995]. Kamalu has defined a threshold steepness at which runoff becomes the dominant erosive agent over rain-splash, or a combination of runoff and rain-splash. This threshold is thought to be soil specific [7].
   The authors begin by  noting the fact that erosion is responsible for great losses of African soil productivity. This situation is exacerbated by the pressures which force Africans to farm on steeper and steeper slopes [Thurrow& Smith 1998).
   Farming and cultivation on these slopes often leads to severe soil erosion.  This is especially the case where African farmers apply traditional methods suited to flat land on slope farms, leading to more serious erosion.  [Oku, 2011].  It leads us to make the point of the importance of the scientific application of African indigenous farming methods to suit the terrain involved. Instead of using traditional tillage involving earth mounds, which is only appropriate on flat or shallow sloped farms and increases erosion on slopes, we can employ other more suitable systems like stonelines or hedging. Furthermore, we can incorporate these methods with  modern soil and water conservation technologies.
   The need for land to cultivate food means we must find a solution which works with this growing trend for steep slope farming.
   Some governments have tried prescribing maximum slopes on which farming is acceptable: for example 12% in Central Africa and 30% in Ethiopia [Grimshaw and Larisa, 1995]. However,  this cannot be enforced and is ignored by famers in need of land to cultivate.
   We must address the question of what technology we can use to reduce soil erosion on these slope farms, as they become more common.Treatments are most effective when combined with or including  a strategy involving use of vegetation to protect against erosion.
Vetiver grass can be used very effectively to slow the velocity of runoff down the slope and hence significantly lessen erosion. The study in fact establishes that vetiver grass used as a buffer strip is more effective at lessening erosion for closer spacing between grass strips. Vetiver grass strips spaced 5m apart were found to adequately slow down the runoff enough to reduce erosion. The positive outcome therefore, is that food production on steep slopes is entirely possible in a sustainable way where we employ soil protection measures like the application  of vetiver grass strips.

Earth Science Events

20-24 March 2018

Earth Sciences for Society

A joint congress organised by
Arab Geosciences Union, African Association of Women in the Geosciences, African Geoparks Network

Venue: Faculty of Sciences, ChouaibDoukkali University, El Jadida, Morocco

VISION: The "Geodynamics, Geo-education and Geoheritage Research Group" of the Geology Department, Faculty of Sciences, El Jadida (Morocco) in collaboration with the Arabian Geosciences Union (ArabGU), the African Association of Women in Geosciences (AAWG) and the African Geoparks Network (AGN) organize jointly the 2nd Arab GU International Conference (AIC2), the 9th AAWG Conference (CAAWG9) and the 3rd International Conference on Geoparks in Africa and MiddleEast (ICGAME3). This joint congress is hosted by the Faculty of Sciences, Chouaïb Doukkali University, El Jadida (Morocco).

References, Selected Reading, etc

 1.   Fletcher, K., Woldemariam, T., Stolle, F., “Scientists Use Google earth and Crowdsourcing to Map Unchartered Forests”, World Resources Institute, 2017.,
2. Habib, E., Yuxin Ma and Douglas Williams,  “Google Earth and Virtual Visualisations in Geoscience Education and Research”.
3. Butler, R., Satellites and Google earth Prove potent Conservation Tool, Yale Environment 360, 26 Mar 2009.
https// _google_earth_prove_potent_conservation_tool
4. Begall,S., Cerveny, J., Neef, J., Burda, H.,  Magnetic Alignment in Grazing and Resting Cattle and Deer, Proceedings of the national Academy of Sciencees, 2008 Sep9; 105(36): 13451-5. Doi:10
5. This is  the principle behind  estimation of geometric areas and other quantities in mathematics by means of the operation known as “integration”
6. United nations University institute for Natural Resources in Africa,  Using vetiver technology to to control erosion and improve productivity in slope farming, Oku, E. E., Aiyelari, E. A., Asubonteng, K. O., Accra, Ghana, 2015.
7. Kamalu, C., The effects of slope length and inclination on the separate and combined actions of rainsplash and runoff, in R.J. Rickson (ed.), Conserving Our Soil Resources, selected papers papers from First International Congress of the European Society for Soil Conservation,  Centre for Agriculture and Biosciences International,1994.

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