Group cachers - group answers will not be accepted as it is impossible to identify that all cachers have been on-site. Each cacher who wishes to log a find must submit their own responses to all the questions (they can all be the same for each member) & identify themselves if a group (rather than individual) photo is taken (send, please don't post). Thank you.
This is an Earthcache that will make you think and apply your knowledge. It's not a "show-up and guess at some rocks" type of cache.
I recently had the pleasure of re-visiting Nottingham and rediscovered the caves. Doing a bit more research unveiled the unique geological history of this area. I hope you enjoy the science lesson and the Earthcache.
The History:
The Park Tunnel was built in 1855 to allow horse drawn carriages access to the The Park Estate from Derby Road in Nottingham, although rather ironically, the gradient of the completed structure was too steep for a horse-drawn carriage to manage.
The Estate has a history as a former hunting park for the Duke of Newcastle, the owner of nearby Nottingham Castle. The term "castle" is used loosely, as the house was more akin to a mansion or perhaps a palace. The original structure was burnt down by unruly and unhappy locals. It’s said that the Duke originally ordered for the tunnel to be built with a specification of a gradient of no more than 1 in 14. The grand tunnel however, was constructed with a gradient of 1 in 12 , thus making it somewhat redundant from the inception.
Thomas Chambers (T.C.) Hine (1813-1899) designed the Park Tunnel (primarily as the main entrance to the Park) and developed the Park as a residential area in central Nottingham for the wealthier members of society. T.C.Hine was also made responsible for the later repair of Nottingham Castle and its conversion into a museum.
These days, the Park Tunnel is used as pedestrian access to the Park Estate. The Park Estate is home to some wonderful Victorian architecture and many fine homes. It has the largest gas street lighting system in Europe which makes it rather atmospheric at night and the skyline is dominated by Nottingham Castle.
The tunnel is still in use, providing pedestrian access from Derby Road, Upper College Street and The Ropewalk to the Park, but remains a hidden gem in the city centre.
Geological History of Nottingham:
“Nottingham was built near a crossing point on the River Trent in the East Midlands of England. Initially, the city developed on a low sandstone hill close to the north bank of the river, which provided a secure, well-drained location above the marshes that bordered the river. Geologically, Nottingham stands at the boundary between Palaeozoic rocks to the north and west, and Mesozoic and Cenozoic strata to the south and east. The area is underlain by coal-bearing Carboniferous Coal Measures, Permian dolomitic limestones, Permo-Triassic mudstones and weak sandstones, Jurassic clays and Quaternary glacial and alluvial deposits.”
Artificial deposits, resulting from the social, industrial and mineral extraction activities of the past, cover the natural deposits over much of the area. This geological environment has underpinned the economic development of the area through the mining of coal (now largely ceased), oil extraction that was important during World War II, brickmaking from clays, alluvial sand and gravel extraction from the Trent Valley, and gypsum extraction from the Permo-Triassic mudstones.
The Permo-Triassic sandstone is a nationally important aquifer, and has also been exploited at the surface and from shallow mines for sand. However, this history of the use and exploitation of mineral deposits has created a number of environmental problems, including rising groundwater levels, abandoned mine shafts and mining subsidence, and, within the city itself, the occasional collapse of artificial cavities in the sandstone and contaminated land left by industrial activities. Natural constraints on development include gypsum dissolution, landslides, rockfalls, swell–shrink problems in Jurassic clays and flooding. Occasional minor earthquakes are attributed to movements related to coal mining or natural, deep geological structures. Thus, Nottingham's geological context remains an important consideration when planning its future regeneration and development.”
Source: Abstract from http://egsp.lyellcollection.org/content/22/1/1
The Science:
Let’s begin with some geological basics. There are 3 main types of rocks: igneous, metamorphic and sedimentary.
Igneous rocks are formed through volcanic processes, and have solidified from a molten state. The Earth is believed to have been entirely molten in its early stages of development. Hence, all other rock types are derivatives of igneous rocks. There are two types of Igneous rocks:
Plutonic/intrusive: Rock from magma rising up from deep under the earth's crust, and solidifies as it cools before it reaches the earth's surface. Examples include granite and gabbro.
Volcanic/extrusive: Rock that was originally lava, hot magma that reached (or exploded from) the surface of the earth before it hardened. Examples include basalt and obsidian.
Metamorphic rocks are formed from sedimentary rocks that are transformed over time. This can result from extreme pressure, temperature and chemical activity. Examples include marble and slate. Metamorphic rocks can be foliated such as gneiss, phyllite, schist, and slate, which have a layered or banded appearance that is produced by exposure to heat and directed pressure. Non-foliated metamorphic rocks such as hornfels, marble, quartzite, and novaculite do not have a layered or banded appearance.
Sedimentary rocks are formed by the accumulation of particles on or near the Earth's surface, and compacted down, often under extreme pressure, creating rock layers. There are three main types of sedimentary rocks: mudstone, sandstone, and limestone.
Useful Vocabulary:
In order to help with your descriptions, here is some geological terminology that you may find useful to incorporate into your responses:
Cross-beds or "sets" are the groups of inclined layers, which are known as cross strata. Cross-bedding forms during deposition on the inclined surfaces of bedforms such as ripples and dunes; it indicates that the depositional environment contained a flowing medium (typically water or wind).
In geology, a graded bed is one characterized by a systematic change in grain or clast size from one side of the bed to the other. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones.
Fine-grained textures generally indicate magmas that rapidly cooled at or near the Earth's surface. Fast cooling prevents crystals from growing very large. The cutoff between fine- and coarse-grained textures is about 1 mm. This terminology relates to igneous rocks.
Colour: colour observed in a mineral sample in white light. With experience, colour can be one of the most valuable of diagnostic properties.
Hardness: the ability of a mineral to resist abrasion or scratching. Measured on a relative scale from 1 - 10 known as Mohs' Scale in which minerals of higher number scratch those of lower numbers. For simple field determinations, a fingernail has an hardness of about 2.5 and the blade of a penknife about 5 - 5.5.
Inclusion: a solid fragment, liquid globule, or pocket of gas enclosed in a mineral or rock; an inclusion is older than the rock in which it's found and is a method of relative dating. Vein: a distinct sheet-like body of crystallized minerals within a rock.
Lustre: the characteristic appearance of a mineral in reflected light, e.g., metallic, pearly, earthy, greasy, etc.
Form: the external appearance of a mineral or aggregates of the mineral, e.g., crystalline, fibrous, stalactitic, dendritic (plant-like), etc.
Cleavage and Fracture: the way that the mineral breaks; if it breaks along planar surfaces related to the crystal structure it is said to show cleavage, but if it breaks irregularly is said to show fracture.
Weathering: the disintegration of rocks on the Earth's surface by the action of rain, frost, heat, wind, etc.
Intact rock strength is a major rock property. It determines the strength of the intact rock block and thus the strength of the entire rock mass. Sophisticated tests are not required to determine intact rock strength, and in the field, "simple means" or impact methods are used (e.g. hammer, scratching, molding, breaking by hand). Rebound values are correlated to rock strength, although this is not a precise science if there are discontinuities in the rock. For our purposes, you can estimate the intact rock strength using the following scale (low to high). Please do not actually use a hammer or break off the rocks!
-
Crumbles in hand
-
Thin slab breaks easily in hand
-
Thin slab breaks - heavy hand pressure
-
Lumps broken by light hammer blows
-
Lumps broken by heavy hammer blows
-
Lumps only chip by heavy hammer blows
-
Rocks ring on hammer blows. Sparks fly!
The assessment of rock mass strength is a key element in any rock excavation, including building tunnels. The rock mass strength defined by a strength envelope is one of the main inputs to be considered to assess stability. High strength indicates high stability and vice-versa. For our purposes, you cannot measure this in the field, so use your best judgement based on your understanding of geological principles.
***
In order to log the find, please send me the responses to the following questions. Q6 is particularly important and should not be ignored.
Group cachers - group answers will not be accepted as it is impossible to identify that all cachers have been on-site. Each cacher who wishes to log a find must submit their own responses to all the questions (they can all be the same for each member) & identify themselves if a group (rather than individual) photo is taken (send, please don't post). Thank you.
Questions:
1. a) What type of stone are you looking at?
b) Which of the 3 main rock types is it an example of?
c) What evidence is there to support your answer for 1b?
2. Looking at the tunnel head on at GZ, with particular reference to the left hand side, describe the formation (e.g. colour, grain size, layer size, patterns, thickness, hardness, cross-bedding, graded-bedding, etc - only refer to what's appropriate for this type of rock). Make sure you pay particular attention to any differences in the rock as you start at the base of the tunnel and move upwards to the first layer of brick. In other words, count the number of layers from the base of the tunnel to the first layer of brick and describe each layer. I am looking for the correct # of layers and the description of each. Be specific and detailed, distinguishing the unique features of the left side of the tunnel in your response.
3. a) What geological period does this specific formation belong to?
b) How do you know (evidence)?
4. Fill in the blanks: This particular type of stone is distinguished by its xxx intact strength and its xxx rock mass strength.
5. Are there layers in the rock? If so, describe the likely depositional environment. If not, why do you think that is?
6. Now, to determine you were actually on site:
TASK #1 - How many (adult stride, walking regularly) paces does it take to walk from the edge of the tunnel at GZ toward Derby Road (forward/slightly uphill if standing at GZ looking toward the tunnel), stopping at the edge of the tunnel? In other words, you are walking from the edge of the part of the tunnel nearest GZ to the other end of the "GZ" tunnel. Not to the steps. No daylight. Not through the second part of the tunnel that leads up to Derby Road. Just the "GZ" tunnel. :) I did many stride tests so there is a small range I will accept.
TASK #2 - Photo of you/your GPS at the EC - send with your answers and do NOT post with you log.
Bonus question: what is this type of rock known as locally (hint: formation and group)?
Bonus, bonus question: what does the title of this EC translate to?
Please ensure that you send your answers when logging a find. Posted logs without the accompanying correct answers will be removed. If you post a find without sending the answers, I will reach out and remind you to send them, but will delete found posts thereafter. If you feel there will be a delay in sending responses, please post a write note and send me your required photo instead. Thank you.