Context
We know that around 350 million years ago, during the early Carboniferous period, volcanoes erupted in what is now Fife, the Lothians and Edinburgh. We are lucky to have several earthcaches showing us the rocks formed at that time. GC21761 'Volcanic mayhem - Kincraig point' is one example further east along the Fife coast. Britain was just south of the Equator. The sedimentary rocks from this period are limestones, sandstones, mudstones and fossil swamp soils deposited in south tropical seas, lakes, deltas, and swamps.
Pillow lavas
The rock formations on the shore at Kinghorn show us what happens when basaltic lavas either erupt under water or reach a source of water while they are flowing. The lava cools fast and forms a ball with a flexible glassy crust on the outside. The molten lava swirls round inside its crust forcing the ball into an oval pillow shape; it grows as more lava fills it until the pressure inside causes the crust to rupture and a new basaltic flow is extruded from the break, forming another pillow. There is much crackling, hissing and spitting as the water boils. This process continues, building up a thick sequence of pillows of a variety of sizes. Eventually the lava stops flowing, the pillows cool completely, they are covered by sediments & form rock. Then they are may be subject to any or all of the forces which shape our earth, for example uplift, folding & erosion.
See & Hear Pillow Formation
In the late 1700s James Hutton realised that the past history of the earth must be explained by what we can see happening today. This video shows pillow lava flowing underwater off the coast of Hawaii, after it was erupted on land and flowed into the ocean. The footage is from the movie "Pele Meets the Sea" courtesy of Richard Pyle at Lava Video Productions. [Link to video on YouTube] Because it happens now, when we find pillow lavas in ancient rock sequences, we may conclude that the area was under water when they formed.
Where to go and what to see
Please remember the shore area is part of an SSSI - take only photos, do not damage the rocks.
From the car park follow the signs for the Fife Coastal Path. They will lead you briefly uphill along Nethergate, under the viaduct and through the playground to the right. The path then goes under the railway again and past the caravan park to a grassy area above the shore.
Along the shore there are many lava flows one after another, sometimes with softer sedimentary rocks in between. The hard lava forms ridges while the intervening rocks have been eroded and allow the sea to come further inshore. Go towards GZ, the co-ordinates for the cache. They are on one of the ridges. Before you get there, look at the ridge. The base of this lava flow has no pillows because pillows will only develop where liquid lava is in contact with water. The interior of the flow, being well away from the water, has not developed pillows. However you can see some pillows at the top of the ridge and when you reach GZ you will suddenly see many, many pillows. The reason for this is that the layers of rock, including the lava flows, have been tilted towards the east-north-east by about 20 degrees so you don't see the top surface until you are on the dip slope.
Note: Start to answer Questions b) and c) at this point.
Notice that the lava is full of holes where gas formed bubbles during the extrusion process. Magma, like a sealed bottle of a fizzy drink, has lots of gas dissolved in it and when it approaches or runs onto the Earth’s surface the pressure on it is reduced so the gas comes out of solution, forms bubbles and escapes or tries to escape into the atmosphere. On cooling, the viscosity of the magma rises very quickly so the gas bubbles may get caught in the sticky liquid to remain in the solid rock as vesicles. This shows that the lava was erupted into shallow water. Sometimes lava pillows are interbedded with sediments from a deep-sea setting, like fine muds. They were erupted along the oceanic ridges. However these pillows differ from the ones you see here in that they do not have vesicles because they have been erupted under deep water and the water pressure is high enough to prevent gas from coming out of solution.
Some of the vesicles have been filled by calcite with small amounts of pink barytes. The minerals which fill vesicles are deposited from hot water after the lava has solidified. Mineral-filled vesicles are called amygdales (Greek amygdalon: an almond) and lava rich in amygdales is described as amygdaloidal.
If it is low tide, look down to where some pillows are smoothed by the action of the waves.
Now return to the coastal path to make your way towards the Eroded Pillows reference point. You will need to leave the path again to reach it. Here you will find a smooth surface where the pillows have been eroded down to intertidal level. Some of the pillows are outlined with white veins. This is because cooling & contraction caused fractures often following the shape of the pillows; these fractures were then filled in with calcite deposited from the hot water. There are several pillow boulders lying around here; they have fallen from their original positions.
Note: Finish your answers to Questions b) and c) at this point.
This is the final point for the cache but if you want to explore further there is plenty more to see along this shore.
Logging requirements
Logging an EarthCache requires that visitors undertake an educational task relating to the specific Earth Science at the site. To log this earthcache first e-mail me the answers to the following questions. Do not put the answers in your log. You may log once you have done this.
a) What 2 things does the presence of vesicular pillow lavas in rocks tell us about the environment at the time & place of their formation ?
b) Counting the lava flow at the cache co-ordinates as 1, how many separate flows consisting of both a non-pillowed base and a pillowed surface are there between here and the final Eroded Pillows reference point ? What does this tell us?
c) Why do you think we can see the shapes of the pillows so well at the cache co-ordinates? Immediately before arriving at the Eroded Pillows reference point you can see part of the same pillowed surface which has not been smoothed by the waves. What do you observe about the spaces between the pillows here? Why do you think this is different from the first site?
Remember it is possible to do this earthcache at most states of the tide but you will see more if the tide is low. [Link to tide timetable]
Well done to Nirikina and Landsbanki for FTF on the 1st of the New Year
We have made use of the Scottish Earth Science Education Forum's Kinghorn Teachers' Guide for this cache page. [Link to the guide]