This is an Earth cache. To log the cache, you must read the geological description of the place and answer the questions.
The easiest way to send the answers is using the message center.
Sand dunes are a rare environment that are usually found near the sea and inhabited by species that are not found anywhere else. In Malta there are a number of these sites, five of which enjoy the highest level of protection because they are located in Natura 2000 sites. This is one of them!
This dune environment is very important for the ecosystem and since it is a very rare and vulnerable environment, the Environment and Resources Authority offers the highest level of protection while Environment Malta ensures that implement their management and conservation plan. This is because the environment is very fragile and easy to damage the rare and unique species that live there.
As you probably noticed, most of the Maltese islands are made up of different stonetypes. Sand dunes are one of the rarest and most vulnerable habitats in the Maltese Islands. Sandy beaches make up only around 2.4 per cent of Malta and Gozo’s coastline.
Please notice, that it is prohibited by law to walk on the dunes, please keep to the marked routes. You will be able to observe everything and answer the questions, without stepping on the dunes.
The Maltese islands are composed of sedimentary rock which was formed under the seawater of Tethys. This began to form about 25 million years ago out of remains of sea creatures, sand and silt. Fifteen million years later tectonic movement lifted the sediment that was on the seabed and thus the Maltese islands emerged above the surface.
The Maltese islands are made up of five main types of rock, which are the following from lowest to highest:
Lower coralline limestone, the oldest rock in Malta since it was the first to be formed at the bottom of the sea between 35 and 25 million years ago.
The globigerina limestone layer forms the surface rock or outcrop of 70% of Malta’s territory and forms large plains. The rock is formed out of shells of marine creatures called foraminifera globigerina. This layer is between 23 and 207 metres thick.
Blue clay the layer of soft blue clay
The greensand, ‘rina’ or ‘ramli’, in Maltese. Greensand is soft, very grainy and porous rock almost totally made up of the broken shells of marine organisms. In this layer one can find a large amount of fossils of creatures that inhabited the bottom of a shallow and sandy sea like starfish, urchins and molluscs.
Upper coralline limestone.was the last layer to be formed on the seabed of Tethys. This type of rock is now found in the highest places of the Maltese islands. This type of rock is sometimes hard, compacted and crystallised. At other times it is composed of softer rock which is easily weathered. Even the colour varies. Some layers are greyish white, while others are yellowish or ruddy (red).
picture from : https://www.malteseislandsweather.com/the-maltese-islands/
Maltese beaches with reddish sand are generally to be found in places where there are exposed clay slopes. In Maltese geology, the clay layer is topped with a deposit of “green sand” which oxidizes to the more familiar red when exposed to the atmosphere. On the other hand, the Maltese beaches with the lighter coloured sand are ones in which coralline or globigerina limestone layers are the predominant surface of their valley sources.
Sand dunes form when the sea and wind pick up and sand is deposited on the beach. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, flat regions covered with wind-swept sand or dunes with little or no vegetation are called ergs or sand seas. The valley or trough between dunes is called a dune slack.
Dunes are made of sand-sized particles, and may consist of quartz, calcium carbonate, snow, gypsum, or other materials. The upwind/upstream/upcurrent side of the dune is called the stoss side; the downflow side is called the lee side. Sand is pushed (creep) or bounces (saltation) up the stoss side, and slides down the lee side. A side of a dune that the sand has slid down is called a slip face (or slipface)
Picture from Wikipedia
Sand hitting sand is more likely to stick; sand hitting a more coherent surface is more likely to bounce.
In geology, saltation (from Latin saltus 'leap, jump') is a specific type of particle transport by fluids such as wind or water. It occurs when loose materials are removed from a bed and carried by the fluid, before being transported back to the surface.
Picture from Wikipedia
In suspension sand grains blow high in the air and then settle. About 1 percent of sand moves this way. Once it's in motion, sand will continue to move until an obstacle causes it to stop. The heaviest grains settle against the obstacle, and a small ridge or bump forms. Because the obstacle breaks the force of the wind, the lighter grains deposit themselves on the other side of the obstacle. Eventually, the surface facing the wind crests, and the lighter grains of sand cascade down the other side, or the slip face. This is how a sand dune may actually move over time -- it rolls along, maintaining its shape as it goes.
Sand dunes are the natural hinterland of undisturbed beaches. They form the buffer zone between the beach and the valley floor behind. They consist of sand, which accumulates at the back of the beach as a result of wind and wave action. They are a sort of middle ground: an area where the predominant material is sand but where vegetation still grows. The sand dune is an area where the underground water flowing downwards from the valley is predominantly fresh to brackish (depending on the season) as opposed to saline water beneath the exposed sand of the beach. This means that sand dunes can support a variety of plant life which is specially adapted to their unique environmental conditions. These organisms have to survive extreme aridity and heat. They also need to adapt to the reality of living in a shifting environment, where the action of wind and water can affect the profile of the landscape.
Sand dunes face several challenges including climate change especially if sea levels rise.
In order to log the cache, the following questions must be answered and conditions must be met:
- At ground zero: describe the dunes (colour, form, slipping side in witch direction, how they are situated refering to the sea...)?
- There are different type of sand here, how do you think the sand has been transported here? From where does the sand originate?
- Are there evidense of unique dune vegetation?
- Take a picture of yourself or something personal at the little lake and the Comino church in the background. (See example)
Add the picture to your log.
- Feel free to add more pictures, but please: do not spoil the answers.
Sources
https://maltainsideout.com/19071/sand-dunes-one-of-maltas-rarest-habitats/
https://tvmnews.mt/en/news/the-five-sand-dunes-of-the-maltese-islands/
https://teleskola.mt/
https://wikipedia.com