A geological dike (or dyke) is a rock formed within a pre-existing rock body. Dikes take two main forms, either magmatic or sedimentary. Magmatic dikes form when magma intrudes into a crack and solidifies. Clastic or Sedimentary dikes form when sediment fills a pre-existing crack.
Magmatic Dikes
Magmatic dikes form when an igneous body intrudes fractures in pre-existing rock formations; this implies that a dike is always younger than the rocks that contain or surround it. Thickness can vary from sub-centimeter scale to many meters. The lateral dimensions can extend over many kilometres.
Dikes are usually near-vertical in orientation, however subsequent activity may transform the strata through which the dike propagates so that the dike becomes horizontal or Near-horizontal. In Contrast, where magma flows along bedding planes between strata they are called intrusive sills.
Sometimes dikes are grouped, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event.
Dikes can vary in texture and their composition can range from diabase or basaltic to granitic or rhyolitic, but on a global perspective the basaltic composition prevails, manifesting ascent of vast volumes of mantle-derived magmas through fractured lithosphere throughout Earth history
Sedimentary dikes
Sedimentary dikes or clastic dikes are vertical bodies of sedimentary rock. They can form in two ways:
When unconsolidated sediment is composed of alternating coarse grained and clay layers the pressure inside the coarser layers may reach a critical level due the pressure or stress imposed by the weight of overlying material, at such pressures the sediment breaks through overlying layers and forms a dike.
Under permafrost conditions with the soil totally frozen, cracks can form and may fill up with sediments from layers above. The result is a vertical body of sediment that cuts through horizontal layers: a dike.
Logging Requirements
To claim this cache you need to answer the following questions:-
From Observation Point 1
Q1: What sort of Dike is the dragon's back?
Q2: Estimate the height in meters of the tallest exposed face of the dike?
From Observation Point 2
Q3: Estimate the thickness of the Dike in meters?
Q4: (Optional): What historic silhouette can you pick out from the terrain that surrounds the Dragon's back?
The following form will assist you in submitting your answers http://goo.gl/forms/PLjkJX4d8B
Feel free to log as soon as you've submitted your answers, I shall be in touch if you are widely off the mark
Find logs without a corresponding answer submission may be deleted.