Unusual Rocks at Mauna Kea

A recent post by Callan Bentley at NOVA Geoblog got me thinking back to a couple long-ago field trips on the Big Island of Hawaii, back during the 1987 GSA Cordilleran section meeting. One of the trips we took was to the top of Mauna Kea, where, after a visit to the W. M. Keck Observatory, we walked down from the peak elevation of 4205 m (13,796 feet) to some elevation quite a bit lower than that, through miles and piles of unusual volcanic rocks of basaltic to andesitic composition. Well, the truth is, I don't really remember exactly how far we walked, but we dropped at least 3000 feet in elevation, and that was pretty difficult for some. A couple people had to bail just below Lake Waiau, because of the altitude. And because I have zero photos of that long-ago field trip (unless a few are left up in Alaska somewhere), go see Callan's photos of his trip to Mauna Kea!

What I found by doing a little online research, was that the unusual (or "weird" - I think I said) volcanic rocks on Mauna Kea are 1) the Hamakua Volcanics, composed of basaltic rocks called picrites, ankaramites, and alkalic and tholeiitic basalts, and 2) the Laupahoehoe Volcanics, composed of hawaiites, mugearites, and benmoreites (Kennedy et al, 1991 and Wolfe et al, 1997 - see below). Not all the rock types above, like picrites, are unusual to Mauna Kea; some can be found on the younger volcanoes of Hawaii.

Mauna Kea is essentially a late-stage basaltic shield volcano, which is what Mauna Loa and Kilauea (along with Pu'u O'o) will eventually grow up to be when they get older. Mauna Kea's end stage Hamakua and Laupahoehoe Volcanics essentially indicate that Mauna Kea is just about done, and is in the post-shield stage of its evolution, although it is still considered dormant rather than extinct, and more eruptions of the end-stage basaltic to andesitic flows would not be unheard of nor totally unexpected (Hawaii CVO site).

As for what these strange or unusual mostly basaltic rocks are, here is the best description I could find, and it approximates what I remember, though may not be 100% precise:

Basalt with extra Na+K = Hawaiite
Basaltic andesite with extra Na+K = Mugearite
Andesite with extra Na+K = Benmoreite
Dacite with extra Na+K = Trachyte
Mugearite or Benmoreite with LOTS of extra Na+K = Phonolite

A Few References and Links:

Kennedy, A. K., Kwon, S.-T., Frey, F. A., West, H. B., 1991, The isotopic composition of postshield lavas from Mauna Kea volcano, Hawaii: Earth and Planetary Science Letters, Volume 103, Issue 1-4, p. 339-353. [Abstract here.]

Wolfe, E. W., Wise, W. S., Dalrymple, G. B., 1997, The geology and petrology of Mauna Kea Volcano, Hawaii; a study of postshield volcanism: U.S. Geol. Survey Prof. Paper 1557, 129 p. [Abstract here.]

On Climbing Mauna Kea
On the Geochemistry of Hawaii Volcanic Rocks
On the Laupahoehoe Volcanics
Wikipedia on Mauna Kea

Twelve Months of Looking for Detachment

I am doing the Twelve Months meme, as per DrugMonkey: the first sentence from the first blog entry for each month of the year. A few things to note: most of these first-posts-of-the-month posts include photos; many, but not all, are part of the Where in the West series. I changed one to a second-post-of-the-month.

• January:
If I were to try to convey the nature of our life here in the hinterland, I might have to use these words: mountains, desert, and lakes; Basin and Range, roadcuts, wide open spaces, and small but cozy living spaces.


• February:
  I wanted to post a link about Joshua trees, because the Mojave Desert is one of my interests.



• March:
  This mountain - seen here from both sides, the east and the west - can be viewed easily from a major road, and is well known for a particular geologic feature.



• April:
  Is it Gold? Or what?



• May:
  The second day started out mostly clear with some high clouds.



• June:
  The weather has seemingly warmed up a little again, but there for awhile it was cold and off-and-on snowy.



• July:
  I'll be away when this post comes out, hiking and camping on Wheeler Peak.



• August:
  Perhaps by now, you've gotten tired of Middlegate Station and want to move on.



• September:
  Yes, I'm back - a lot of catching up to do - and then, back to work.



• October:
  There we were, finally on the boat.



• November:
  It's been a while since I've done this - not since August as a matter of fact.



• December:
  Back in early November, BrianR of Clastic Detritus won the Where in the West contest that you can sometimes find here on this blog.

So, that's mostly places in the western US, a bit of geology here and there, a trace of rocks or minerals, some miscellaneous discourse, and some hiking around. Kind of a good review, at least for me! ;)

A Clue - Where in the North, December

Well, having had exactly zero takers on the Where in the North photo I posted a few days back, I'll add a little clue: the fjord in the photo is one of the longest ones in the world!

In the Field

What is my favorite place to do field work? That's the subject of the November Accretionary Wedge (#14), which is being hosted by Dave Schumaker at Geology News.

I'm a little like Chris Rowan, I suppose, in that I'm not sure I really have a favorite field area - unless the entire Mojave Desert might count as a field area, or the entire state of Nevada, or... Well, you get the idea. So, my favorite field area is probably whichever one I happen to be working on when I'm out in the field.

The photo above shows some tree-covered to not-so-tree-covered hills in the center or north-center of the Northumberland caldera. The photo, which looks west towards the east front of the Toiyabe Range, was taken from the western approach to the Northumberland Mine, a closed-down gold mine at the top of Northumberland Pass, and the view is just a little to the south of West Northumberland Canyon. The highest peak in the caldera part of the photo, hides the area I got stuck out in one night back in the late 70's. Yeah, maybe that shouldn't make this a favorite area!

I spent a lot of time here, first doing some stream-sediment and rock sampling, walking around here and there, mostly from the tops of drainages to the bottoms, looking for high scintillometer readings to indicate the presence of uranium. Later, I spent quite a bit of time mapping parts of the caldera: the northern, central, and southern parts - bits and pieces, here and there, a lot of interesting rocks, formations, faults, ring-fractures, flow-domes, slide blocks, and rocks younger and older than the caldera itself. After that, I was given a fairly large budget for the time, and we started drilling like crazy, at one time having 3 core rigs and 1 or 2 rotary rigs drilling at once (way too many at once, but fortunately 2 were about to leave). That was the first year.

The place sticks in my mind partly because I spent so much time there, from 1978 through 1981, but also because of the people I worked with, the size and fascinating geology of the area, and all the stories that go with the area. I will be writing more!

Above, you can see another view of the northern part of the caldera. This photo takes off just to the right (or north) of the first photo, and continues north, where the tuff of Hoodoo Canyon takes over, covering the Northumberland Tuff. The view looks west, like the first one, across Big Smoky Valley to the east front of the Toiyabe Range, and our first-year camp at Bowman Creek can be picked out beneath the roundish, partly snow-covered mountain just a little bit right of center (and way southeast of Nome - oh, that's an unrelated song!).

Accretionary Wedge #14: Favorite Places for Field Work

Fall Decorations with Duct Tape

A still life:

Decorations at our little house, with duct tape close at hand (barely visible, on the right!).

You never know when you're going to need it! ;)

Well, I'm back, and am way behind on blog reading, etcetera, and find I have a meme to do (thanks ReBecca!) and an Accretionary Web or two. Hopefully I can get to these things sometime shortly!