Shira Lava Cave – Amazing Geology of Kilimanjaro

At the coordinates you will find the Shira Cave, which is a primary lava cave. Interesting to mention is that the Shira cave, as our guide has told us, has been used for overnight stay by many porters also him during the last decades.

But let's have a closer look on different types of lava caves. Due to the orientation of the lava cave on site, I have limited myself to horizontally arranged caves in the listing, although there are various other types.

Lava tubes

Lava tubes are the most common in the lava tube category. A lava tube is formed when this thin lava flows down the volcanic slope in a kind of channel during an eruption. Since the flow speed and the temperature of the lava are lowest at the edges and especially on the surface of the lava flow, the lava solidifies there first. Starting from the edges of the lava channel, a kind of roof grows over the lava flow. Below the "roof" the lava continues to flow as long as the volcano supplies supplies. After the end of the eruption, the flow of lava subsides and the level in the tube drops because the lava continues to flow down the slope due to its low viscosity. Eventually, after the rest of the lava solidifies and cools, a cavity remains.

Depending on the slope, terrain and lava viscosity, different types of lava tubes are formed. Multilateral tubes often run in parallel, often forming branched and anastomosing tubes. Multi-stage tubes are those that sit directly on top of or below another tube, sometimes above or below multiple tubes. Lava flows can contain a mix of multi-tiered and multi-sided tubes. Another shape a lava tube can take is the tube-in-tube, which can form within lava tubes when the linings of the walls are weak enough to tilt inward and form a new floor over the old. Tubes within tubes are generally found to form during the last lava flowing through the main lava tube.
Such drained tubes commonly have step markings on their walls marking the different depths at which the lava flowed, called flow ridges or flow lines, depending on how much they protrude from the walls. Lava tubes generally have pāhoehoe floors, although these are often mined from the ceiling. A variety of speleothems can be found in lava tubes including a variety of stalactite shapes commonly known as lavacicles, which can be splash, "shark tooth" or tubular varieties.

Surface tubes

Surface tubes are drained rivulets or runners of the same highly fluid lava flowing in lava channels. They form on an existing hardened surface and most are too small to get inside. They are created by flowing lava that inverts. Sometimes referred to as "toes", they are believed to be involved in the growth (lengthwise) of lava tubes. They usually form when vents, channels, or lava reservoirs overflow. They are very shallow and are usually below the surface for the first few meters. Some surface tubes may connect to lava tubes deeper below the surface. Surface tubes typically have a uniform wall thickness and a semi-circular cross-section, with the flat side down against the surface where they were formed. Branching is common, and broad dendritic networks are not uncommon. The widths range from about one decimeter to several meters. The length depends primarily on an uninterrupted supply of lava and ranges widely. Surface tubes are much more numerous than is commonly believed, as most are subsequently buried.

Inflation caves

Inflation caves are usually small chambers, they form when lava is pressurized and pushes on outer rock. They are also called sub-crustal lava caves. The lava then later drains away, leaving an inflationary cave. In some cases, volcanic gases exert pressure on solid or semi-solid lava and a bubble of thin rock is formed. These bubbles are sometimes large enough to qualify as a cave. Inflated caves can be confused with lava tubes as they often share many of the same characteristics. The cavities are sometimes also referred to as blisters.

	Lava spreads from a skylight above a tube, or by overflow from a crater or a lava channel. The spreading lobes grow by a process of 'budding' in which a small lobe develops a skin, and is inflated by the lava pressure until the skin ruptures in one or more places.
	Lava escaping through the rupture develops new lobes and so on. Stagnant areas solidify leaving liquid-filled chambers (in larger lobes) or a network of small proto-tubes.
	The lava completely flowed out of the sub-crustal cave and formed the cavities. The lava is almost completely solidified.

Lava mold caves

Lava mold caves form when lava flows around trees or even large dead animals. The encapsulated material eventually burns or decomposes, leaving a cavity imprinted with the original shape. As a rule, these caves are not very large, at the same time they can become complex, for example, when groups of fallen logs touch and then form caves that can go in several directions, where the resulting cavities intersect. Elephant caves are known from the Nyiragongo volcano in Africa and one in the shape of a Tertiary rhinoceros is known from Blue Lake, Washington.

Sources
Wikipedia.de
expedition report kilimanjaro caving
showcaves.com

Pictures
showcaves.com
Own drawings

To log this Eartcache, go to the given coordinates and answer the following questions via email or the message center to me

1. Measure or estimate the dimensions of the Shira Cave in height, width and depth.

2. From the list of caves above, which type of lava cave best descibes the cave here?
   How would you justify that regarding the information from the listing?
   Can you find evidence for your assumption inside or outside the cave?

3. Look at the walls to the right outside the cave (right when looking to the entrance). What can you see? Describe also the structures and shapes. How do you think this came about?

4. Take a photo of yourself and/or a personal item (e.g. your GPS) and attach it to your log!