Page 2 of 2

PostPosted: Feb 5, 2007 5:34 pm
by bigalpha
BenC wrote:knotty wrote:
What causes the different colors in lava? Some of the caves here in Idaho have as many as 7 different colors(7 different flows). Eache flow has there own color. The color is brightes on the surface or glaze but there is color all through the porus section as well.

I think We're getting into Bowens Reaction theory.

Bingo. That's why I asked which colors are associated with the lava flows. Not to mention the Yellowstone Hot Spot. Re-melting the already differentiated crust/lava

Re: lavatubes pictures

PostPosted: Feb 5, 2007 6:16 pm
by NZcaver
mgala wrote:BTW, we've just put some pictures from kazumura and kipuka kanochina on our site:

Nice shots - it's good to see some familiar places and faces.

But who is/are the photographer(s)? :question:

PostPosted: Feb 5, 2007 9:14 pm
by knotty
Thanks for the good info.

PostPosted: Feb 5, 2007 10:40 pm
by Teresa
hewhocaves wrote: ... _moon.html

Initially these eruptions are very violent and produce a lava known as rhyolite. Huge calderas of up to 30 miles in diameter are formed when these devastating eruptions take place. Later a more fluid lava known as basalt flows onto the surface and covers the rhyolitic flows. Yellowstone National Park, the area where the hot spot is believed to be located at this time, is the place where catastrophic rhyolitic eruptions last occurred 600,000 years ago. Craters of the Moon represents the second stage of the eruptions where fluid basaltic lava covered the landscape as recently as 2,000 years ago.

rhyolite is a extrusive (quickly cooling version of granite - essentially a light color) basalt is darker.

Basalt has more iron, magnesium and manganese, and more dark feldspars, and less quartz. What are called mafic minerals are usually dark black, to dark green in color. That being said, rhyolite is *not* necessarily light-colored. Ash fall (just what you think it is) unaltered rhyolites are often powdery, and light colored (lavender, pink, yellow, cream) as well as lightweight. Yellowstone rhyolite is um--yellow. However, don't judge a rhyolite by its color. Most of the Missouri rhyolite porphyries are black to dark purple or maroon, with white or pink feldspar flecks. These are generally ashflows--ash explodes very hot, comes to earth, forms thick hot layers, remelts, and flows down the mountain, recooling slow enough to grow the crystal flecks.

as for why the mineral composition varied - the off-the-cuff reaction is that its near a subduction zone (to the west) and so the magma coming upwards is essentially the melted continental plate which would have quite a vareity of elements associated with it. However, there is probably a more specific / altenate explanation to it involving the Yellowstone hot spot. but regardless, the point is that there was a mix of materials which changed over time forming the different colors.

Making a grand assumption that Idaho is not unlike Washington State or Yellowstone, you've got basically three varieties of volcanic magmas-- mafic (deep crustal origin, heavy-thin basaltic--like Hawaii) felsic ( shallow crustal origin,lots of quartz and feldspar, rhyolitic thick, explosive--like all the Mt. St. Helens flows except the one Ape Cave is in) and intermediate (halfway between the two-- rocks like andesite, diorite--lots of light feldspars, some dark heavy minerals, not a lot of quartz--similar to the Sierra Nevada.)

There is also a process called magma fractionation-- basically a magma with a lot of all components in it will settle like a cooling stew, with the light minerals rising to the top like fat, intermediate minerals staying in the middle like broth, and heavy minerals sinking like the meat carrots and potatoes. If you drain off one of the separated components sideways down a fracture you get different lavas. Or, if the light stuff blows off, then all that remains for the next reheating is the heavy stuff.

The process of fractionation is how and why you can get rhyolite, basalt and andesite flows very close to each other, or even on top if each other over time.

Olivine, peridotite and similar minerals will give you green and black colors.

Iron can give you a suite of colors from black to yellow. Black, brown, orange, maroon, purple, lavender, bluish, green, yellow...

Manganese gives you black.

Magnesium can give you pink or purplish.

Sulfur-- bright yellow or orange.

Metals and semi-metals like lead give a variety of golds, silvers, gray and brass.

Copper blue, green, bright brown or orange.

Calcium and sodium give white. Potassium--purple or pink.
Quartz--clear, white or gray if pure.

There are others, but these are the main rock coloring elements and minerals.

PostPosted: Feb 6, 2007 10:11 am
by knotty
Thanks Teresa
WOW. I like your answer. I knew some of what you said from my geology class 20 years ago but have forgotten much. I cant tell you how much I appreciate your input. I am armed for discussion with my fellow cavers.
Knowledge is a great weapon.

PostPosted: Feb 6, 2007 10:59 am
by bigalpha
Man, do I miss taking my Geology classes already. I didn't know that Yellowstone Rhyolite was yellow. That's pretty cool. Any idea why? I have a piece of that Missouri Rhyolite. We took our Petrology field trip to Johnson's Shut-In's.

Idaho (Snake River Plain) is the old path of the Yellowstone hotspot, but I don't think the SRP rhyolite is yellow. I wonder why?

PostPosted: Feb 6, 2007 12:33 pm
by Teresa
Sad to say, I've never been to Idaho.

The park isn't actually named for the stone, though the Grand Canyon of the Yellowstone is indeed yellow, cream and pinkish in places.
"The canyon's colors were created by hot water acting on volcanic rock. It was not these colors, but the river's yellow sandstone banks at its distant confluence with the Missouri River, that occasioned the Minnetaree Indian name which French trappers translated as roche jaune, yellow stone. "NPS geology site.
In essence, after the ash fell, the resulting ash was pressure steamed, and quick oxidized, changing the color. That might relate back to the original question about volcanic colors in hydrothermal vs non-hydrothermal areas. I've actually seen rhyolite from Mo. where the outside was oxidized yellow, but it had a purple/black core when broken.

PostPosted: Feb 6, 2007 12:44 pm
by bigalpha
My girlfriend went to field Camp at Pocatello, ID; and did a report on SRP but I don't think she got in depth enough to find out the color of the rhyolite.

Do you think the yellowing of rhyolite is a common occurrence with hydrothermal areas and volcanic rocks?

PostPosted: Feb 6, 2007 8:07 pm
by Teresa
Not a clue about the yellowing of rhyolite as a rule of thumb. I'm not enough of an ig-met type to generalize.

PostPosted: Feb 6, 2007 9:26 pm
by bigalpha
Ah, i thought maybe you would know something about it. Thanks for all the awesome info, though! :D

PostPosted: Feb 9, 2007 2:47 pm
by knotty
here is preety pics of caves in Idaho

PostPosted: Mar 16, 2007 11:06 pm
by Bruce Rogers

Last November, Ben Sainsbury "Karstcreature", posted a question about lavacicles (yes, I'm a bit behind on my web surfing...). Dave Bunnell replied, aptly abstracting Kevin & Carlene Allred's JCKS article of Dec., 1998.

I thought that a bit more of history might be of interest to readers of this list. The idea of small, molten pockets of lava degassing and squeezing lava out of hairline cracks and pinholes on lava tube walls goes back to at least the mid-1980's. The late Dr. Aaron Waters (world-class vulcanologist) & I were speculating just how these forms came about with Dr. Keith Howard (USGS vulcanologist and former astronaut candidate). After reading Drs. Tom Wright and Reggie Okamura's 1977 USGS paper on filter pressing of lava in Hawai'i, Keith had come up with the idea of some sort similar partial melting of the still-plastic lava behind the lava tube wall as the driving force. He thought that resulting segregating and gas build-up would force the lava out of tiny lining cracks and such to form the soda straws and helictites Lack of time and instrumentation to verify this, however, caused it to slip by the wayside.

It was. however, Kevin & Carlene Allred who managed to pull all the points together, backed up with newer analytical methods, and actually get the idea out on print in 1998.

Bruce Rogers, earth scientist on a good day

PostPosted: Mar 16, 2007 11:52 pm
by Bruce Rogers

Last November Ben Sainbury posted several questions about the composition of lava tube speleothems and speleothem-like forms (those made of lava and not by solution/deposition of minerals). In the resulting discussion several posters speculated on what sort of minerals one might find in lava tubes. For a good synopsis, read Carol Hill and Paolo Forti's "Cave Minerals of the World", 2nd ed.

In my lava tube cave minerals work in California, Oregon, Washington, and New Mexico over the last 44 years I have found a suite of minerals of calcareous, sulfate, sulfite, oxide, and silicate composition.

From Lava Beds Nat. Mon area in northern CA, 13 secondary minerals, mineraloids, and rocks were found as speleothems or speleothem-like forms. These include: ice - H2O (common, especially seasonally), gypsum - CaSO4.2H2O (uncommon), barite (rare), calcite - CaCO3 (very common), two unnamed sulfite and sulfo-carbonate salts - Na2SO3.7H2O and Na.SO4.CO3.nH2O (rare), alpha-cristobalite (very common), opal C-T - SiO2 n H2O (rare), opal-A - SiO2 nH2O (common), "amorphous" silica - SiO2 (common), uric acid (moderately common), amberat (common), and basalt and/or andesitic basalt (ubiquitous). Earlier reports of native sulfur in several caves was apparently made on color alone and was in error.

In other lava tubes in southern CA, the "collective" we (Russ Harter) have also found trona, Na3(CO3)(HCO3) 2H2O.

The "amorphous silica" is most probably extremely fine crystallized SiO2 "opal" of some form, with the individual crystallites being smaller than the length of an x-ray that was used to identify these minerals.

In many coralloids the speleothem's interior is composed of alternating white and tan-colored layers. The white is apparently cristobalite and the tan calcite. These apparently reflect changing groundwater seepage into the lava tubes with cristobalite forming in more arid times and calcite in the moister times. It is still uncertain if these cycles are yearly or for longer periods of time.

The mineralogy of El Malpais Nat. Mon. in New Mexico is similar, but with the addition of burkeite - Na6(CO3)(SO4)2, epsomite - MgSO4 7H2O, glaserite - (K, Na)Na(SO4)2, mirabilite - Na2SO4 10H2O, malachite - Cu2(CO3)(OH)2, and thenardite - Na2SO4.

Bruce Rogers, earth scientist on a good day

PostPosted: Mar 17, 2007 12:34 am
by Bruce Rogers

In Feb., "Knotty" asked what colors lava flows. In the return posts the most comprehensive was that of Teresa, wherein she lists colors resulting from inclusion of various elements in minerals. This is a good start for most mineral colors, but as with most things, this can be misleading at times. The temperatures and chemical compositions of lava differ from those of many minerals and thus the colors listed by Teresa are generally valid for many minerals, they may not always apply to lava.

Generally, most lavas are some shade of dark gray or black. This results form the inclusion of iron and magnesium mineral grains in the lava. Lavas cooling in lava tubes near open windows often are colored some shade of red, orange, or yellow as a result of oxidation of the iron minerals within the lava.

In some lava tubes/surface flows, the lava takes on more surprising colors. Some lavas have a high concentration of olivine, a green mineral that may make the lava and resulting sand derived from the lava a dark green color (in gem form this is referred to as peridote, the mineral ancient alchemists ascribed as protecting from "vague terrors of the night" - certainly a mineral most cavers would want to have around...).

I offer this observation communicated to me by Dr. Ken Hon of the USGS Hawai'i Volcanoes Observatory. On the Big Island, Ken made the only successfully dash into and back out of an active lava tube to my knowledge while collecting wall samples. Not to steal his thunder, but the tube wall mineralogy in an active tube is vastly different than that we see in now cooled tubes. Many of the walls have a bright blue cast that appears to be the mineral ferrite or alpha iron.

Bruce Rogers, earth scientist on a good day