Welcome to the Parwan Sinkhole EarthCache. It was created to celebrate International EarthCache Day 2018. A word about safety before you get too excited. There are double lines along the centre of the busy road near the sinkhole. There's plenty of safe, off-road verge parking here. I suggest you park at least 3 metres clear of the road to make sure you're legal and safe. Do not drive across the double lines. If you choose to walk across the road please watch for fast moving cars and trucks. Entrance to the sinkhole is best made at the end of the fence near the lone fir tree north of the sinkhole. The grass is always long here so please be alert for snakes.
Sinkholes can be defined as depressions or holes in the ground caused by the action of underground water erosion that results in some form of collapse of the surface layer.
As with most things geological, classifying sinkholes can be complicated. One way to classify them is to divide them into two basic types. The first type are called cover-subsidence sinkholes. They are created over time when parts of the soil at the surface sink slowly into underground cavities created by water action. The second type are called cover-collapse sinkholes. They appear suddenly, usually when the underground cavities get too large and there's nothing below to hold the weight of the soil above. Both types of sinkholes are formed by the same basic underground water action. If you see a sinkhole on the news it's probably a cover-collapse sinkhole that has appeared overnight in a populated area.
Sinkholes vary in area from a few square metres to hundreds of hectares and from less than 1 to more than 100 metres deep. Some are round like shallow bowls or saucers but others have vertical walls. Some hold water and form natural ponds but some don't. The Parwan sinkhole is an irregular, elongated shape about 35 meters long,18 meters wide and about 3 metres deep at its extremities.
Put on your EarthCache-goggles and sensible footwear before you go exploring the sinkhole. I'll ask you four progressively harder questions, and you send me a message with your answers. I welcome requests for hints. If your answers are very wrong, I'll ask you to try again. Feel free to log your find immediately. Please be mindful that if I haven't received your correct answers after seven days I'll reluctantly delete your log entry.
Q1. Part of the west wall has collapsed. Some of its rocks have fallen into the sinkhole. What might be the reason for the collapse?
Q 2. Below the narrow layer of topsoil there are rock walls. What are the two main colours of the rock walls?
Q 3. Why is the lower rocks' colour different from the upper rocks?
Q 4. This is the last and hardest question. Apart from any litter, there is something in the western side of the sinkhole that is obviously modern and unnatural. What is it? (It's approximately 50 mm wide but you can't pick it up.)