These volcanic breccias on Aegina island, Greece exhibit large cavities with smooth, rounded walls. Is there a way to find out what used to be inside those cavities? Was it just gas or fluids with metals?
From what I remember of geology (admittedly a VERY long time ago), these were indeed gas-pockets that got trapped in the flow as it solidified.
Dear Mr. Issigonis,
at first glance I suspect different morphological types which may indeed be interpreted as escape or vent structures for gas and/ or fluids in a volcanic/volcaniclastic environment. I have seen a wide range of such structures but I am very reluctant to hand down a verdict without having a more detailed information on the types of host rock (pyroclastic, volcanic rocks). If you release some more data on the host rock or can provide us with an overview of the volcanic edifice we might be able to get you a bit closer to the solution.
The only structure I would dare an interpretation is No1. It looks like a smoker, which you can find submarine and sublacustrine. But even this clear answer still resides on shaky ground. The other is a so-called cementation process. Fluids and gas migrate along very porous and permeable parts of these pyroclastic deposits (?). They may lead to some kind of cementation and enduration of the wall rocks. When undergoing erosion and denudation these case-hardened parts got sculptured out of the overall lithological units. Things like that you can find in sediments of the Kattegat and in Bulgaria (Pobitite Kamani).
But gas, fluids and cementation may play a role in the built-up of these structures.
Looking forward to your description of the geological setting.
Best regards
Harald G. Dill
Trapped gases or liquids, it would be interesting to analyze them from deeper cavity locations, provided the proper techniques could be developed. It would help tell us about atmospheric or seawater compositions in the past.
Please be kindly informed that we already have very simply and inexpensive new and Innovative technique to explore all types of cavities and determinate their contents either gases or liquids or soft material that approximately has not any flexiblity. ( The technique is applied and proven in the field ).
Best Regards,,,
Dear colleagues,
I think Dr. Diabat has thrown a stone in the water and the waves are going to touch the shoreline now. That was necessary. His answer can be interpreted as a general statement in favor and against the current Q & A processes. Based upon the data available it is sufficient because everything left is getting more and more a rambling around and mere speculation. What will we achieve through this? On the other hand if his wording sparks a more detailed information about the environment of formation, lithology, age of formation, chemical and mineralogical composition then the outcome is well received and the "waves have washed away the silt from the shell". I have tried to work for almost 40 years based on facts and not to indulge into speculations.
This is neither complaining about the present process which we are involved in, nor is it an attempt to grind it to a halt. It is to contemplate what the current process is like and to try and get it back on track. I feel from time to time you have to make such a "mental pit stop" and rethink the process.
Please apologize for this philosophical detour.
Best regards
Harald G. Dill
First I should apologize for not providing any geological background to this question. I have not done a geological study of the area. Geological studies have been carried out by many. However, it is not clear from them what the environment was like when the island was created by repeated volcanic eruptions.
Perhaps, the description by the Indiana University team (2014) comes close enough. They see 3 stages of eruptions spanning 3 million years (4 my to 1 my), with the area in question being part of the biggest eruption event during the Pliocene with mostly dacitic volcaniclastic flows that formed at or near sea level
I see opportunities for research work in many aspects of the volcanic phenomena on this island. Local residents and the many visitors have been asking many interesting questions -the subject of which we are discussing now being an example -that sometimes geologists are not sure how to explain.
Thus, the geology of Aegina island has not been recreated to the level that archeology has recreated the life of people during the Classical Age for example (500 - 300 years BC)
Dear Mr. Issigonis,
thank you for providing some more background information. I think you have shown us the pathway to a solution by yourself. The volcaniclastic rocks near the sea level with an expected reactions between the molten magma and the water at depth will direct our thoughts to a steam-heated reaction in the vent system on one side, giving rise to these varied structures and a possible phreatomagmatic process leading to the pyroclastic deposits on the other side, shown on the photographs. Another part of the story also essential for an interpretation is difficult to assess. It is the geomorphological/sedimentological part in terms of sea level fluctuation and vertical movements on the island. Maybe we should leave some room for proper investigations at site by geologists working in the field on the island.
Best regards
Harald G. Dill
It may be like Allard Jan Van Marle said due to traped gases
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