What is Blue Rock?

[Super8]

Hi,

Could someone explain what they mean when you're digging and you hit blue rock?
Is this it?

[url]http://en.wikipedia.org/wiki/File:Scoria_AmsterdamIsland_5.jpg
[/url]

Or could someone point me to some pictures or a diagram of the layers of the different kinds of earth on the Big Island?

Does anybody have a real close up picture of cracked earth from some of the more recent flows?

I found these pictures in a surf. If Allan is on here, thanks for the amazing stills.

http://www.laughtermedicine.us/hawaii/ka...index.html 4th, 5th, and 6th ones.

Looks like Scoria to me. Is blue rock underneath this stuff?

Thanks[8]

[bluesboy]

Aren't you the person that knew how to divert the lava flow? And you don't know what blue rock is?

[rainyjim]

Blue rock is basalt. Typically I believe it refers to a much more dense / less porous basalt lava rock -this is the really hard rock mainly found underneath Aa - if I recall correctly.

[Carey]

Yup, dense Basalt, usually core of a`a flow, also found in wayyy past glacial areas (these were the premier adze mines, having the densest basalt...Basalt tools from our islands have been found throughout Polynesia, most likely because of the superior quality for tool forming...

Scoria is often formed on fast pahoehoe flows, were the gases do not have the time to 'off gas'. (fun to be here when a pahoehoe flow is cooling & puffing as the gases expand (the rock actually tinkles like heat creaking glass)

A`a flows are more crumbly & usually advance slower, bearing in mind that flows can change back & forth, sometimes mid channel..the hot core of the slower moving a`a flow usually forms the blue rock

One easy thing for geologist in Hawaii to answer - "what type of rock is that?", hands down, even with eyes closed, "Basalt" will most likely be correct

[VancouverIslander]

The difference between pahoehoe and a'a is based almost entirely on the relationship between shear forces and the viscosity of the lava. You will tend to see more a'a on steeper slopes since that increases the shear force beyond the ability of the viscosity to remain fluid - kind of like when you stretch silly putty too fast - the shear force overcomes the viscosity of the silly putty and it snaps. Stretch it slower and it remains more liquid. I'm not entirely sure that Carey is correct that a'a is slower as it is the faster pace on steeper slopes that cause it to become 'chunky', but I'm sure someone (possibly even Carey) will correct me if I'm wrong.

Source: http://volcano.oregonstate.edu/what-are-...-they-form

[Super8]

quote:

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Originally posted by Carey

Yup, dense Basalt, ...

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Thanks Carey and rainyjim. I assumed that's what "blue rock" was referring to, but since it's a relative term, I wasn't sure. I am thinking it's technical term is Alkali Basalt, from wikipedia, " Alkali basalt is a fine-grained, dark-coloured, volcanic rock characterized by phenocrysts of olivine, titanium-rich augite, plagioclase feldspar and iron oxides. For similar SiO2 concentrations, alkali basalts have a higher content of the alkalis, Na2O and K2O, than other basalt types such as tholeiites. They are also characterized by the development of modal nepheline in their groundmass (visible at highest magnification on a petrographic microscope) and normative nepheline in their CIPW norms. Alkali basalts are typically found on updomed and rifted continental crust, and on oceanic islands such as Hawaii, Madeira and Ascension Island."

bluesboy, I am that person. I don't see the academic or engineering communities putting forth ideas to stop 10,000+ home from burning down and all of lower Puna from becoming isolated. What was your suggestion?

[john the architect]

When I built my first home in HPP it had a raised level supported by two reinforced concrete water tanks in "castleblock", an ICF concrete from. That composite structure will even better than a solid concrete first level to resist high heat and maintain its structural integrity.

Anyone else who built a home with "castleblock" lower level would also have lava resistance.
If you are into ultimate survival for your building, that is the stuff.

John Maloney
310.562.0362
johnmaloney3@me.com
Hawaii Architect AR8082
www.jmagreenbuilding.com

[Derrick Barnicoat]

Interesting I did't think Hawaii had any blue rock. Guess there is a some down there somewhere.

[Rob Tucker]

When I was doing my foundation I just touched on blue stone at the bottom of the footing. Drilling in to pin the stone was tough. I had rarely dealt with such a hard stone.

[Super8]

VancouverIslander, A'a, your correct, the flow does move faster. I think vesicularity is also determines the classification. Beyond what you encounter on the surface, is it still crumbly like cinder, or is it igneous like a cement with very large chunks? I fell on that stuff in Kau. Don't hurry your scurry to take piss down there. There were vast "fields" of but I didn't go didging through it. I'd like to know what the ground is like 3 feet down in there.

john the architect, castleblock sounds like good stuff if it's what i found on the net. can you say why it would perform well?

Rob Tucker, I wish you had pictures!! When you drilled in, what kind of tool did you use? What all did you go through to get to the blue stone?

Thanks guys,

[8]