On a recent trip out with Team Smurf, I was tail end charlie, and looking about, and spotted some interesting geology. We are here to look at vesicles.
We are here to learn about vesicles.
You are here to look for a rounded rock next to the path, that has many holes in it, these are known as vesicles. So what are vesicles? As the magma cooled, gases within it, expanded and formed a cavity, these cavities are known as vesicles, basically a bubble of gas, formed as the rock cooled and solidified. It is a cavity left by the gas. Vesicles are more common with abrupt changes of temperature and pressure; as gaseous escapes are linked to temperature and pressure which in turn control the vesicular texture, so can be seen more in extrusive rocks, as intrusive rocks as they cool do not allow for abrupt temperature or pressure changes, so lesser vesicles. When the magma which eventually forms the rock, starts to cool, rapid cooling, leads to gases which have formed in the eruptive phase to start to rise, these then form pores or vesicles on the surface of the rock.
There are different types of vesicles.
Flattended / elongated vesicles
These vesicles rock are flattened because the rock flowed before it solidified.
Amygdales
If a vesicle is filled in by a secondary mineral it is described as an amygdale.
Vesicle cylinders
These are vertical pipes filled with bubbles, that are differentiated from the rest of the magma flows during the cooling and crystallisation process. These suggest that there was a high level of water content in the magma before eruption took place As the bubbles of gas rose, the vapour migrated into low pressure, vertical areas which then result in vesiscle cylinders.
Pipe vesicles
These form near the base of the lava flow at the crystallization front. They have a characteristic umbrella shape, which is a result of vesicules rising slowly through stagnant lava to the base of the upper cooling surface, where they spread laterally and form horizontal vesicle sheets.
Vesicle segregation veins
These are layers of vesicles, which are thought to be the result ofthes repeated cycles of magma flow, and and gas release during the breakout of the magma.
Elongate vesicles
These indicate deformation of the gas bubbles trapped in partially solidified lava and magma flow.
Dense clusters of vesicles
Dense clusters of vesicles surrounded by fine-grained rock are thought to be a result of spatter. Spatter is an accumulation of hot, fluid clasts (rocks), which agglutinate (gather together) on landing. Very fluid magma spatter may also splash on landing. This spatter can form a pile, and the dense cluster of vesicles is the evidence of gases escaping as the rock cools.
Subrounded to rounded vesicles
Vesicles, which are subrounded to rounded, display an increased size, and decreased frequency upwards towards the the flow interior, at which vesiculation largely ceases. Above the flow interior, the concentration of vesicles increases and vesicle size decreases through to the top of the flowing rock or magma.. Because thicker magma flows take longer to solidify, their interiors typically have near-complete loss of vesicles from the lower and middle portions
This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.
(1) Please examine the rock and tell me which side of the rock has the most vesicles, is it the north side or south side?
(2) Is the whole rock covered by vesicles?
(3) Please find the largest vesicle, how wide is it, and how deep is it?
(4) Are all the vesicles the same shape, what shapes can you see, please describe them.
(5) Using the answer to question 4, please tell me, what type of vesicles you can see.
(5) Near the path is a round life saving ring, please have your picture taken on the rock with the vesicles on, with yourself and the ring in the picture.