Volcanos EarthCache
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First of all, this place also gives you spectacular views on the north-west part of the Dingle Peninsula. Dingle is not only spectacular for its very Special climate but also for the atmosphere, the views and the geology.
You have Clogher Head in the west and Sybil Point in the north and in between you have An Dram with the strange hole in the Cliffs and the small beach which is lovely but not recommended to swimming…
To the north-east you see the Three Sisters and behind the Brandon Mountain Massive… Enjoy the views before you do anything else…!!!
A short extract from a book referring to Dingle (which we highly recommend for Dingle):
(source: Steve MacDonogh: The Dingle Peninsula)
The Great Geological Riddle
In 1856 members of the London Geological Society descended upon the Peninsula in their top hats and best clothes to investigate Dingle rocks. When they came to Ferriter’s Cove south of the Three Sisters at Smerwick they found to their surprise that the rocks were Silurian, full of fossils and much older than the Devonian sandstone rocks which constituted the Three Sisters,and indeed the majority of Peninsula. At the time no-one knew about the mid-Atlantic rift, continental drift and plate tectonics, so the fact that Ferriter’s Cove shared the same geology, and similar fossils, with the coast of Newfoundland was perplexing. It wasn’t till well into the 20th century that these things began to be better understood.
A short geological history of Ireland
(source: (visit link)
Oldest rocks
The oldest rocks in Ireland occur on a small island at the very north of Ireland, and in the West. These are coarsely crystalline banded gneisses produced by strong metamorphism of Palaeoproterozoic igneous rocks. Most Precambrian rocks of northwestern Ireland are part of a belt of rocks called the Dalradian Supergroup. This extends from the west of Ireland into Scotland and is composed mainly of metamorphosed marine sedimentary rocks, but includes volcanic rocks and metamorphosed glacio‑marine deposits from the Precambrian glaciations known as “Snowball Earth”. The Dalradian rocks were deposited during the fragmentation of Rodinia, which rifted apart about 600 million years ago to form the Iapetus Ocean.
Iapetus
The Iapetus Ocean began to close in the early Ordovician. The axis of Iapetus ran through central Ireland, approximately from the present day Shannon Estuary to Dundalk Bay. Present day northwest and southeast Ireland lay along the margins of separate continents – Laurentia in the north, and micro-continents peripheral to Gondwana in the south – with the Iapetus Ocean several thousand kilometres wide in between. Lower Palaeozoic sedimentary rocks were deposited on these continental margins. Iapetus suture Subduction gradually closed the Iapetus, with volcanic arcs building up along both margins and within the ocean. Thick successions of Ordovician volcanic arc rocks are preserved in the West and Southeast of Ireland, with large gabbroic to granitic plutons in the West representing the deep intrusive level of a magmatic arc. Lower Palaeozoic sediments preserved in an accretionary prism that is the geological continuation of the Southern Uplands of Scotland – that today forms a wide band of greywacke and shale that spans the border between the North and the Republic. As the ocean narrowed, several separate Silurian sedimentary basins were formed. Final closure of Iapetus occurred during late Silurian to early Devonian times, amalgamating the foundations of Ireland on the southern, equatorial margin of Laurussia. The resulting Caledonian Orogeny raised a composite mountain chain which runs from the Appalachians of North America, through Ireland and Britain, to the Arctic Circle in Norway. Continental collision was accompanied by voluminous granite emplacement, creating large batholiths around Ireland.
A geological map Ireland can be viewe here: (visit link)
As the Iapetus Ocean closed the ocean plate was pushed beneath the continate plate. Melting produced a chain of volcanic Islands which are today part of the Dingle Peninsula.
Tropics
During the Devonian Period, Ireland was located on landmass in which the climate was semi-arid with seasonal rainfall. Erosion of the Caledonian Mountains supplied sediment via south-flowing rivers to extensive alluvial plains. Present-day southwest Ireland was the site of the thickest non-marine Devonian sequence in Europe, with more than 6km of sedimentary rocks deposited. Fossil footprints forming several trackways are preserved in Devonian siltstones on Valentia Island in Southwest Ireland. They were made by the first known tetrapod, a primitive amphibian, as it walked across a fluvial plain. As the first discovery of this type in Europe and the oldest in situ record of an amphibian animal, the site is now protected as an important part of Ireland’s heritage. By the end of the Devonian, Ireland lay near the equator.
Global sea-level rises caused a northwards transgression, depositing coastal and shallow marine early Carboniferous sediments. These siliciclastics were followed by extensive shelly limestone deposits in a shallow water shelf sea. Early Variscan extensional tectonics caused block-and-basin faulting; shallow shelf areas were sites of relatively pure biogenic limestones and deeper basins were filled with fine-grained muddy limestones and calcareous mudstones. One of the best places to see the Carboniferous limestones is the Burren, Co. Clare. Here the limestones are extensively exposed at the surface and have hardly been disturbed by earth movements; individual bedding surfaces can be traced for kilometers.
The Burren limestones are one of the best places in the world to study karst landscapes. Caves, dolines, turloughs, sink holes and disappearing rivers can all be found in abundance in the Burren and surrounding limestone areas. The Upper Carboniferous in Ireland saw a return to siliciclastic depositon related to global sea level changes. Deep-water basinal sediments and marginal coal measures were followed by shallow water deltaic sandstones and shales. The best places to see these rocks are on the coast of Co. Clare, from the Shannon Estuary to the Cliffs of Moher. Irish coalfields have thin coal seams which are relatively uneconomic to work. At the end of the Carboniferous, Ireland was on the northern edge of the Variscan orogenic belt and its effects were relatively slight, except for the south where the rocks were folded into broad open anticlines and synclines with a wavelength of several kilometres. The anticlines are now ridges underlain by Devonian Old Red Sandstone, while the synclines are now valleys floored by Carboniferous limestone.
Ireland lay just north of the equator by the beginning of the Permian on the new supercontinent of Pangaea. Rocks of this Permian “New Red Sandstone” desert and succeeding Cretaceous chalks are preserved on land mainly in the northeast where they have been protected from erosion by the covering of Palaeogene basalt lavas (part of which forms the Giant’s Causeway). Later in the Triassic, great thicknesses of sediment and evaporites accumulated a subsiding basin, including more than 400m of rock salt, which is commercially extracted. Early Jurassic mudstones over 100m thick and rich in ammonite fossils are visible along the foreshore 30km northeast of Belfast. At the time of writing, this section is being considered for the global stratotype section for the base of the Jurassic.
The coords bring you to a parking location to check out the views and the information you may need to log this cache.
You will find on the one hand an information board and a few meters nearby a significant stone.
To log this cache please answer the questions and maybe load up a foto from you or your team or just from the scenery:
1) When you look towards the rocks of An Ghraig. What kind of mineral stones do you identify?
2) Which Ocean divided Ireland during the Silurian Period into two parts?
3) How many different geological minerals (and periods) occur on Dingle Penin and which is the oldest? To which town is it reffered to?
4) You see the significant stone beside you. It has a very special characteristic, what is it and what do you think was the function of this?
Please answer the questions parallel to your log, if there are any things unclear we will contact you. Enjoy the view!!!
Additional Hints
(No hints available.)