Located in the western end of KwaZulu-Natal province of South Africa on the road between Underberg and Mokhotlong, Lesotho it is a route that connects Kwazulu-Natal and Lesotho. It is a notoriously dangerous road, which requires the use of a 4x4 vehicle. This pass lies between the border controls of both countries and is approximately 9km in length and requires above average driving experience. It has occasional remains of vehicles that did not succeed in navigating its steep gradients and poor traction surfaces, and has a catalogue of frightening stories of failed attempts at ascending the path over the Northern Lesotho mountains. While South African immigration at the bottom of pass prohibits vehicles deemed unsuitable for the journey, the Lesotho border agents at the top generally allow vehicles of all types to attempt the descent. The Border between the two Countries closes at 4:00 pm every day and the Pass is often closed due to weather conditions, especially during winter.
Geology of the area.
Introduction
The Sani Pass ascends the escarpment of the Drakensberg range of mountains. Dramatic outpourings of lava spread across much of Gondwana about 180 million years ago heralding the start of Gondwana breakup. Remnants of these once extensive lavas now form the Lesotho highlands and Lebombo mountains.
A layer of igneous basalt rocks for a layer up to 1.5 kilometres thick. This accumulation of Jurassic age basalt flows can be seen along the entire length of the Drakensberg Escarpment. The magma (molten rock) made its way to the surface along a complex system of fractures. Throughout much of Kwa Zulu Natal, evidence can be seen via sills (horizontal) and dykes (vertical) of the basalts. One can also see evidence of dolorite feeders where similar feed material cooled much quicker in smaller systems.
Crystallisation of magma within these fractures formed dolerite sills and dykes.
Sills are horizontal intrusions of igneous rock. Dolerite sills are common throughout inland KZN in sedimentary rocks of the Karoo Supergroup.
More on the geology
During the Pre-Cambrian Era, volcanic eruptions in the area resulted in lava covering large sections of the Southern African sub-continent. In the Palaeozoic Era, wind and water deposited thick layers of shale, mudstone and sandstone, now known as the Karoo Supergroup, over the ancient primary rock. When Gondwanaland began to break up 200 million years ago, the resultant forces caused the extrusion of magma, known as Drakensberg lava, through fissures and cracks in the Earth's surface. In the Drakensberg region it capped the sedimentary rock formations with layers of solid basalt up to 1500 m thick. Weathering reduced the range's size, and caused the plateau to recede. In modern times, continued erosion has exposed some of the underlying sediment – known as the Little Berg (which is primarily sedimentary in composition). The majority of the range is basalt, as a result of continental upheaval and volcanic activity in the Pre-Cambrian era. Many of the lava flows are characterized by amygdaloidal zones. Many of the primary minerals within the basalts have been subjected to varying degrees of deuteric alteration which has led to the formation of clay, as well as chlorite and zeolite to a lesser extent. Some interstitial glass has also broken down to form clay. These secondary minerals, together with zeolites which occur notably as amygdaloidal fillings, mean that many of the basalts break down rapidly on exposure. The breakdown results from the expansion which occurs when the clay minerals swell on absorption of water
Geological map of KZN and surrounds
Note the Drakensberg Basalts in Red
Now to explain some of the jargon:
> Deuteric alteration : Textural and mineralogical changes occurring within an igneous rock during the final crystallization stages of the molten rock. It usually occurs at well above room temperature, but some changes can be delayed for a few years after solidification.
>Amygdaloidal: volcanic rock texture in which small volatile cavities or vesicles are filled with secondary minerals – visible as a “spotty” texture of the basalt where small white (quartzitic minerals) have been deposited in these gas bubbles. In some cases (not here unfortunately) you can get large cavities filled with stunning crystals such as amethyst form amygdaloids.
>Interstitial: this refers to open areas within a solid structure (so in this case caused by gas "bubbles" within the molten igneous basaltic magma as the basalts were extruded).
In order to substantiate your visit and be able to claim this Earthcache, a number of questions need to be answered and submitted to the cache developer, via e-mail.
You could also post a photograph in your log or an interesting geological POI you have observed during your trip – why not a whole bunch? It is so stunning and there are so many. {Optional}.
1. Describe the various rock layers one sees between the base of the pass (Sani Pass Hotel) and the top where you now are standing. Especially mention the colours, grain sizes and orientation of the layers and approximate thicknesses.
2. Find a basalt exposure where amygdales are present. Describe their shape, colour and if any crystals were visible.
3. Describe some of the interesting things and experiences you had on your trip.
NOTE: You may log your visit prior to approval, but e-mail submissions that do not meet the above criteria will be deleted.
