GC788EG Pumice in Preveza (Earthcache) in Greece created by Yngve Myrslok

This cache is temporarily unavailable.

GeoAwareIB: Hi

Please see the log by Terratin.
The rocks in this EC has been incorrectly identified and she is willing to help with the revision of the lesson so the cache does not get archived.

Please reach out to her ASAP.

Regards, GeoAwareIB

GC788EG ▼

A cache by Yngve Myrslok Message this owner

Hidden : 7/2/2017

Difficulty:

Terrain:

Size: Size: other (other)

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Geocache Description:

At this old ruin in Preveza you can find pumice rocks. As you walk around here take a look at the amazin ruin and the beautiful surroundings.

[English]

Pumice is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light colored.

Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano. The unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solubility of gases (including water and CO2) that are dissolved in the lava, causing the gases to rapidly exsolve (like the bubbles of CO2 that appear when a carbonated drink is opened). The simultaneous cooling and depressurization freezes the bubbles in a matrix. Eruptions under water are rapidly cooled and the large volume of pumice created can be a shipping hazard for cargo ships.

Pumice is composed of highly microvesicular glass pyroclastic with very thin, translucent bubble walls of extrusive igneous rock. It is commonly, but not exclusively of silicic or felsic to intermediate in composition, but basaltic and other compositions are known. Pumice is commonly pale in color, ranging from white, cream, blue or grey, to green-brown or black. It forms when volcanic gases exsolving from viscous magma form bubbles that remain within the viscous magma as it cools to glass. Pumice is a common product of explosive eruptions and commonly forms zones in upper parts of silicic lavas. Pumice has an average porosity of 90%, and initially floats on water.

Scoria differs from pumice in being denser. With larger vesicles and thicker vesicle walls, it sinks rapidly. The difference is the result of the lower viscosity of the magma that forms scoria. When larger amounts of gas are present, the result is a finer-grained variety of pumice known as pumicite. Pumice is considered a glass because it has no crystal structure. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in water. After the explosion of Krakatoa, rafts of pumice drifted through the Pacific Ocean for up to 20 years, with tree trunks floating among them. In fact, pumice rafts disperse and support several marine species. In 1979, 1984 and 2006, underwater volcanic eruptions near Tonga created large pumice rafts, some as large as 30 km that floated hundreds of kilometres to Fiji.

There are two main forms of vesicles. Most pumice contains tubular microvesicles that can impart a silky or fibrous fabric. The elongation of the microvesicles occurs due to ductile elongation in the volcanic conduit or, in the case of pumiceous lavas, during flow. The other form of vesicles are subspherical to spherical and result from high vapor pressure during eruption.

Close up on pumicestone

To logg this cache you have to send the answers to these questions to the CO:

1. How is pumicestones created?
2. At this beach, are the pumice scoria or vesicular?
3. Why is it that pumicestones can float?
4. What are the most common size of the pumicestones here in Preveza?
5. This is not something that you have to do, but I would like if you posted a photo in the log aswell =)
I would like to get the answers in english =)

[Source]
https://en.wikipedia.org/wiki/Pumice
https://sv.wikipedia.org/wiki/Pimpsten
http://www.baramineraler.se/sv/produkter/pimpsten
http://www.pumex.se/?gclid=Cj0KCQjwnazLBRDxARIsAECdaut-tGLwGuGsvRVxCd_Qpodq0nmDCqeJS8jo07eHvKYnwKI2_2agD8gaAte0EALw_wcB
http://www.give2all.org/10/2013/06/pimpsten-fakta.html

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