Welcome to the Spillars Cove Chimney. The Chimney here in Spillars Cove is a prominent narrow sea stack, and is the remains of an igneous intrusion. It is a great example of a resistant mafic igneous dike which cuts across the surrounding sedimentary rocks.
Sea Stacks
Sea stacks - isolated pillars of rock standing in the ocean - are common and striking erosionl landforms. These geological landforms consist of a steep and often vertical column or columns of rock near a coast, formed by erosion. Coastal erosion or the slow wearing of rock by water and wind over very long periods of time, thousands or even millions of years, in fact, causes a stack to form. Through processes of coastal geomorphology they are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Eventually, erosion will cause the stack to collapse, leaving a stump.
Over time, this too can get broken down, causing the stack to collapse, leaving what's known as a sea stump. Any stack could become a stump as the water breaks down its base. Stacks can provide important nesting locations for seabirds.
Even Newfoundlands strong, rocky coast is susceptible to erosion and as an abundance of these natural features, they are excellent examples of the power of the ocean.
Rock Types
Rocks are said to be the hard matter which forms after the solidification of magma and because of various other geographical phenomena. There are generally three main types which include igneous rocks, sedimentary rocks, and metamorphic rocks. Among these, igneous rocks are said to be the primary rocks as they occur first, then sedimentary rocks form and then the formation of metamorphic rocks happens due to geological processes on these previous two rock types. Igneous rocks are formed after the solidification of magma and can be of two types i.e. Intrusive and Extrusive. If rock forms below the surface of the Earth is known as Intrusive whereas if it occurs above the surface of the Earth, it is known as Extrusive rocks. Mafic rock is an example of Intrusive igneous rock.
Igneous intrusion
An igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and compositions. Intrusions are broadly divided into discordant intrusions, which cut across the existing structure of the country rock (rock native to the area), and concordant intrusions that intrude parallel to existing rock bed.
Dike
A dike or dyke, is a sheet of rock that is formed in a fracture of a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin.
A magmatic dike is a sheet of igneous rock that either cuts across older rock beds or through a contiguous mass of rock. It is formed when magma fills a fracture or a crack in the older beds and then cools and solidifies as a sheet intrusion. The dike rock is usually more resistant to weathering than the surrounding rock, so that erosion exposes the dike as a natural wall or ridge. It is from these natural walls that dikes get their name.
Sedimentary rock is made of minerals and sediments that build up over time. Sedimentary dikes, also called clastic dikes, are formed from sedimentary rock. Clastic dikes are formed when sediment fills a pre-existing crack.
The thickness of a dike is much smaller than its other two dimensions, and the opposite walls are roughly parallel, so that a dike is more or less constant in thickness. The thickness of different dikes can range from a few millimeters to hundreds of meters, but is most typically from about a meter to a few tens of meters. The lateral extent can be tens of kilometers, and dikes with a thickness of a few tens of meters or more commonly extend for over 100 km. Most dikes are steeply dipping; in other words, they are oriented nearly vertically.
In order to log this earthcache, please send a private message to the cache owner with the answers to the following questions:
1. [REQUIRED] In accordance with the updated guidelines from Geocaching Headquarters published in June 2019, photos are now an acceptable logging requirement and WILL BE REQUIRED TO LOG THIS CACHE. Please post a photo in your log of yourself or a personal item with the sea stack in the background to prove you visited the site.
2. What is the elevation at the top of the sea stack? Reference Point Top N 48 39.823 W 53 03.350
3. What direction does the stack run?
4. What is mafic magma?
5. Is this an example of a discordant intrusion or a concordant intrusion?
6. What other examples of erosional landforms do you see in the area?