Between a Rock and a Hard Place

Science Snap (#29): African Fairy Circles

Elspeth Robertson July 14, 2014

Mysterious Fairy Circles dotting the Namibian grasslands. Credit: Neurgens

If you’re wandering among the arid desert that stretches from Angola to South Africa, you may notice the ground pot-marked by millions of circular barren patches. These striking features are known as “Fairy circles”, and can grow up to 15 meters in diameter. Tall grasses often surround these circles, further accentuating these miniature crop circles. How these Fairy Circles form is hotly debated. Theories have to account for their non-random location, and a lifespan 30-60 years where they grow in size borefore grassland eventually invades them again.

Oral myths of the Himba people attribute the circles to gods and spirits and traditionally they are thought to have spiritual and magical powers. My favourite myth, however, is that these Fairy Circles are scars in the landscape where a dragon breathed out toxic gases.

Unfortunately, a scientific explanation likely exists. In 2013, Juergens published an article supporting a popular theory that sand termites are responsible. The paper states that sand termites form the circles by eating grassroots to expose the soil. Once exposed, the soil more easily absorbs, which ultimately helps maintain the grasslands in extremely dry conditions. However, the sand termite theory has been critiqued for assuming correlation with causation, as Juergens suspects that termites are responsible because they’re the only species consistently observed at the circles. Thus, sand termites were identified by a process of species elimination.

In contention to the termite theory, Cramer and Barger (2013) believe that Fairy Circles are a consequence of natural competition in grasses. They suggest that landscapes with a mixture of grasses form “self organizing” circles due to underground competition for water resources. Both hypotheses have aspects that remain inconclusive, thus no theory currently prevails. They currently struggle to explain why circles appear across a variety of regions, soil and vegetation types and furthermore, no one has ever observed termites gnaw out a circle. Perhaps there is still room for a supernatural cause after all.

Aim high, shoot low? UK recycling rates missing the target

Charly Stamper July 9, 2014

In 2008, the EU set a target for member countries to achieve a 50 % household recycling rate by 2020; last week, an amendment raised this figure to 70 % . The graph below shows the latest available data for the UK.

Proportion of household waste recycled in the UK. At the current rate of increase, the UK will not meet the 70 % by 2020 target set by the EU. Data source: DEFRA/National Statistics

It doesn’t take a rocket scientist (or an Earth scientist for that matter) to work out that at the current rate of progress, we aren’t going to hit the 70 % required by 2020. This fact was noted by the UK government at the release of the latest annual statistics in 2013, but becomes even more pertinent given the updated EU directive.

Of course, tackling household waste is a many-layered complex problem, and by only focussing on recycling we are in danger of neglecting other important aspects of resource management. For example, recycling statistics don’t take into account material that people reuse, the decreasing use of certain types of packaging, or domestic waste disposal (such as composting). Furthermore, many believe that we should be moving towards whole system change, where recycling is a last resort.

However, the fact still remains that over half of the municipal waste collected by local authorities in the UK is going to landfill. This figure has declined steadily since 2000, but every year, as a nation we still send 14,000,000 tonnes of material to a big whole in the ground; that’s the equivalent of 241 kg per person.

In 2012/13, local authority collections in the UK sent 14 million tonnes of waste to landfill. Source: DEFRA/National Statistics

There are many reasons why we put waste in the big black bin, rather than recycling it, with prohibitive factors ranging from socio-economic to logistical and geographic. Undoubtedly, there is a large variation in the recycling rates achieved by local authorities in the UK: 73 out of 352 authorities are averaging over a 50 % recycling rate; whereas the average proportion of household waste recycled in London boroughs falls to a disappointing 32 %.

Variation in household recycling rates, by UK local authority. Source: DEFRA/National Statistics

Further examination of available data reveals kerbside food recycling is only offered by around a third of local authorities, covering a total of 6.5 million people or a mere tenth of the population in the UK. Some of the neglected may take it upon themselves to compost; the rest simply don’t have the resources or motivation.

These are just some of the issues we will need to tackle in the coming years. However the UK government, and the EU as a whole, move forward to try and meet the target it’s clear we cannot rest on our laurels. The current rate of 43 % is a start, but it’s nowhere near enough.

Science Snap (#28): The Eye of the Sahara

Elspeth Robertson July 7, 2014

The Eye of the Sahara. Image credit: NASA

Surrounded by thousands of square miles of ubiquitous desert, the “Eye of the Sahara” peers out from the Earth’s surface and at nearly 50 km wide, its easily visible from space too. The “Eye of the Sahara” is known as a Richat Structure, a geological feature consisting of a series of alternating circular layers of sedimentary, igneous and metamorphic rock, exposed by erosion.

The “Eye of the Sahara” is located in central Mauritiana and is also known as Guelb er Richat. The sheer size of the Eye meant it wasn’t discovered until space exploration took off. So here’s a challenge, find it on Google Earth.

The “Eye of the Sahara” was formed by a magmatic intrusion, which forced its way up and warped the overlying rock layers into a dome shape. The intrusion initially never reached the surface, but now erosion has effectively sliced dome’s top off, exposing its inner structure.

The Eye is extremely symmetrical, a striking feature that led scientists to interpret it as an impact crater. This idea was dismissed, however, when scientists began researching its structure. Nevertheless, scientists still can’t explain exactly why the Eye is so symmetrical.

The layers of rock inside the eye are visually distinct as each varies in colour, composition, and resistance to erosion. Inside the Eye there is a rich variety of geological rocks, including rhyolites, gabbros, carbonatites and kimberlites. Quartzite layers are highly resistant, but breccias and volcanic rocks are more prone to weathering and erosion. Intrusive kimberlite plugs beneath the Eye suggest the presence of deep and large alkaline magmatic intrusions and was likely responsible for uplifting the Eye.

Science Snap (#28): Brandberg Massif, Namibia

Elspeth Robertson June 26, 2014

The 120 million year old Brandberg Massif, Namibia. Image credit: NASA

Brandberg Massif is Namibia’s highest mountain, but if you look from above, you’ll notice it’s no ordinary one. Brandberg is a single mass of granite that pierced its way through the Earth’s crust into the Namib Desert. Looking at the Landsat 7 image, Brandberg is a circular dark and steep-sided mountain, imposing itself over the desert below. It reaches height of 2.5 km and stretches across 31 km.

Nowadays, the landscape is geologically quiet but the Brandberg intrusion formed over 120 million years ago and marks a period in the Earth’s history where volcanism was rife due to the break up of the supercontinent Gondwana. The majority of the Massif is composed of homogeneous medium grained biotite-hornblende granite. However, to the west there is a 2 km diameter pyroxene-bearing monzonite and in the south it is crosscut with arfvedsonite granite dykes and sills. As the Massif protrudes from the landscape, it influences local climate by drawing in the rains. The rain then percolates through the granites and washes out through springs.

Apparently, if you reach the granite for sunrise or sunset, you’ll see it glow red under the suns rays. Appropriately, the locals call it Daures, “the burning mountain”.