Saturday, April 19, 2014

I can only beg ... suspend judgment until the whole case shall have been presented

“Hillers trachyte is a pale gray paste with large white crystals of feldspar and crystals large and small of hornblende.  This describes the variety at hand.”
This is one of the least eye-catching rocks in my kitchen.  No one picks it up, ponders it, asks questions.  Yet it’s special for me ... and for the history of geology.  I found it one morning on the picnic table at my campsite, on top of yellowed sheets of paper with notes and sketches.  They were not there the evening before.

I brewed a cup of coffee and sat down to read the mysterious missive.  This is what I found [notes in italics are mine]:
The Henry Mountains are not a range, and have no trend; they are simply a group of five individual mountains, separated by low passes and arranged without discernible system. [here there was an arrow to the diagram above] ... they stand on the right bank of the Colorado River of the West, and between its tributaries, the Fremont and the Escalante.

Geological exploration had shown that they were well disposed for examination, and that they promised to give the key to a type of structure which was at best obscurely known[emphasis added]

If the structure of the mountains be as novel to the reader as it was to the writer, and if it be as strongly opposed to his preconception of the manner in which igneous mountains are constituted, he may well question the conclusions in regard to it ...  I can only beg him to suspend his judgement until the whole case shall have been presented.

It is usual for igneous rocks to ascend to the surface of the earth, there issue forth and build up mountains or hills by successive eruptions [arrow to diagram below]
Mountain of Eruption
The lava of the Henry Mountains behaved differently.  Instead of rising through all the beds of the earth’s crust, it stopped at a lower horizon, insinuated itself between two strata, and opened for itself a chamber by lifting all the superior beds.  In this chamber it congealed, forming a massive body of trap.  For this body the name “laccolite” (Greek: cistern and stone) will be used.  [hmmm ... I thought the term was “laccolith”]
[arrow to sketch above] The simplest type of Henry Mt. structure is a lenticular mass of trap above which the strata are arched [this diagram looked very familiar, where had I seen it?]
or they have made these subterranean mounds at many different levels so as to produce a structure of which [arrow to sketch above] is an ideal cross section.

Contemporaneous and subsequent denudation have left the existing phenomena:
Mt. Ellsworth
Mt. Hillers
[there was one more sheet, and it was there that the author’s identity was revealed]
If these pages fail to give a correct account of the structure of the Henry Mountains the fault is mine and I have no excuse.  G.K.G.


I was stunned!!  "G.K.G." -- that's Grove Karl Gilbert, one of the greatest 19th-century geologists of western North America.  That familiar diagram is his classic cross-section through a laccolith, from his study of the geology of the Henry Mountains.  In fact, Gilbert had camped at this very spot at the southeast base of Mt. Hillers.  Had he dropped his field notes?  No, that couldn't be.  He was last here 136 years ago.  They must have been left on the table by some ghostly visitor in the night ... 
Grove Karl Gilbert in 1894; National Academy of Sciences Archives.
I reread the yellowed sheets, paying close attention to every detail.  An hour passed unnoticed and by then the day was getting warm.  But no matter.  I loaded my pack and drove around to the south side of Mt. Hillers to hike up to the base.  I wanted to see sandstone spurs, hogbacks, revet crags and trap for myself.
Modern-day view of the south base of Hillers.
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In 1869, the great explorer and geologist John Wesley Powell was traveling down the Colorado River through today’s Utah.  He spotted an isolated cluster of peaks to the west, which he called the Unknown Mountains.  They would become the last range to be named in the Lower 48 States.
The Unknown Mountains from the air.
View from Google Earth (click on image).  Lake Powell (Colorado River) in southeast corner.
Powell thought the Unknown Mountains looked like volcanos.  This was of great interest because there was a debate raging as to whether volcanos were 1) “craters of elevation” or 2) craters built from piles of debris accumulated through repeated eruption (geology was still a young science).  Even from a distance Powell could see these mountains were domed and had dark masses of lava-like rock, suggesting “craters of elevation.”
  Mt. Hillers from the west.
Five years later, Powell was in charge of the US Geographical and Geological Survey of the Rocky Mountain Region, and the Unknown Mountains had become the Henry Mountains, named for his physicist friend, Joseph Henry.  Powell directed Grove Karl Gilbert to take an exploratory expedition into the Henrys and perhaps settle the question as to whether volcanos were craters of elevation or of debris.  But the question was never answered, for Gilbert found no volcanos.

They left York, Utah, south of Salt Lake City, on June 20, 1875.  It took 20 days to travel the 200 miles to the Henry Mountains, by mule.  Trails ranged from good to unknown.  On August 22, they established Camp 38 very close to today’s Starr Springs Campground, where I found the mysterious notes and rock.
The old Starr Ranch.  The springs have long attracted humans; there's a BLM campground there now.
Gilbert spent two weeks in the Henrys in 1875.  He found no evidence of volcanic activity, and by the end of the visit was beginning to think about alternative models.  He returned the next year and stayed for two months.  When his report was published, the Henry Mountains became the type locality for a new geologic structure -- the laccolith.  Gilbert used “lacune” in his early field books, but then chose “laccolite” as the formal name. Later he was persuaded to change to “laccolith” because “-ite” typically applies to rock types rather than structures.

Gilbert’s laccoliths were distinct from other igneous structures recognized at that time.  Unlike volcanos, molten igneous material did not reach the surface.  Nor did it solidify deep below, as did masses of granite and related rocks.  Instead, magma was intruded into rock layers near the surface.  Furthermore, the “trap” deformed the overlying strata -- a novel concept.
"Half-stereogram" of a laccolith showing deformed sedimentary strata above, from Gilbert's report.  In his early field notes, he sometimes called these bubble or tumor mountains.
The deformed sedimentary rocks on the south flank of Mt. Hillers are especially striking.  "On this side a half dozen spurs show fragments of red rock as sketched ... inferior rocks tilted almost to the vertical and interspersed with dikes.  Moreover these sandstone hogbacks seem to trend in a curve around the mountain as far as they extend.”
Field sketch of the south base of Hillers, showing prominent hogbacks (click on image to view).
"Base crags of Hillers" from Gilbert's field notes.
Base crags of Hillers from the air.  Photo courtesy Jack Share of Written in Stone.
“revet-crags” and “bold spurs of trap” (dark rock near horizon)
"inferior rocks tilted almost to the vertical"
We wandered among the revet crags and bold spurs of trap for several hours.  They were extremely photogenic but it was getting hot.  So we headed back down to the car, and drove east and north to Hanksville.  With the Henrys in constant view, and Gilbert’s words and sketches bouncing around in my head, it was hard to keep my eyes on the road.
Eastern flank of Mt. Hillers.  Photo courtesy Jack Share of Written in Stone.
But while the Henry Mountains contribute almost nothing to our direct material interests, they offer in common with the plateaus which surround them a field of surpassing interest to the student of structural geology.  The deep carving of the land which renders it so inhospitable to the traveler and the settler, is to the geologist a dissection which lays bare the very anatomy of the rocks, and the dry climate which makes the region a naked desert, soilless and almost plantless, perfects the preparation for his examination.  -- G.K.G.
From "Map of the Henry Mountains by G.K. Gilbert.  From a model in relief." (1880)
Henry Mountains in southern Utah; click on image to view. 

Sources

Gilbert, G.K.  1880.  Report on the geology of the Henry Mountains, 2nd ed.  Dept. of the Interior, US Geographical & Geological Survey of the Rocky Mountain Region, Washington DC.  full PDF here

Hunt, C.B.  1988.  Geology of the Henry Mountains, Utah, as recorded in the notebooks of G.K. Gilbert, 1975-76.  Geol. Soc. Am. Mem. 167.

Share, Jack.  2011.  The Henry Mountains Laccolithic Complex on the Colorado Plateau at Written in Stone ... seen through my lens


Saturday, April 12, 2014

Tree-measuring -- an alternative to Spring

"Man is the measure of all things ...
of things that are, how they are ...
and of things that are not, how they are not.” (Protagoras)
This tree measures 58.4 feet in height.
It’s time for April’s Tree-following post, but there’s nothing to report as my cottonwood doesn't appear to have changed at all since a month ago.  So I decided to measure it.  “It is interesting and easy to determine the height of certain favorite trees” wrote Woodbridge Metcalf in Native Trees of the San Francisco Bay Region (1970, University of California Press).  I rounded up a crew and we headed into the field to determine the height of the cottonwood, using various methods.  It wasn’t as easy as Dr. Metcalf suggested, but he was right that it was interesting.
The day was cold, gray and windy, with sunny moments and occasional flurries of light snow.

1.  Simple Estimate

Mike guessed at the point on the tree 10 feet above the ground, and estimated it took 6 of these lengths to reach the top, for a total of 60 feet.  Then the cold wind drove him away.

2.  Hypsometer

We next used a yardstick as a hypsometer (instrument for measuring height).
“Measure on the ground to a distance of 25 feet from the tree.  Standing at this point, hold the ruler vertically at arms length (25 inches), with the zero point on a line from your eye to the base of the tree.  Then ‘sight’ along the ruler to the top of the tree.  Note the reading at the point where the line of sight intersects the ruler scale.  If the line of sight intersects at 20.5 inches, the tree is 20.5 feet tall.  For a taller tree, mark off a distance 50 feet from the base of the tree and double the reading on the ruler.” (Woodbridge Metcalf)

The cottonwood clearly was taller than 25 feet.  In fact we used four times the distance to get a good perspective and so had to quadruple the intercept.  My arm-length is 21 inches so I stood 84 feet from the tree.  The intercept on the yardstick was 14.5 inches, making the tree 58 feet tall (4 x 14.5).
Dave tried it with his 24-inch arm-length and came up with 62.5 feet -- big difference, maybe because it was hard to keep the yardstick vertical in the wind.

3.  Shadows

“On a sunny day the height of a tree that stands on fairly level ground can be determined by relating the length of its shadow to the shadow of a staff of known height.  The staff shadow is to the height of the staff as the tree shadow is to the height of the tree.”

When the sun came out for a bit, we applied the Shadows method.  A 4-foot staff cast a 3.25-foot shadow.  Unfortunately the tree shadow ended in a stand of shrubby willows, so we tried lying on the ground among the willows to see where the tip would land.  Two of us independently estimated the shadow to be 40 feet long.
If X is the height of the tree, then 3.25 is to 4 as 40 is to X, or 4/3.25 = X/40. 
X = 160/3.25 = 49.23.  The height of the tree is 49.2 feet.
Pesky willows to right of tree caught and distorted its shadow.
4.  Trigonometry

The engineer on the crew wanted to use trigonometry.  This involved measuring the angle from level of a line from the ground to the top of the tree with an iPhone tilt-meter app, and then finding the tangent (see table) and calculating the height.  The angle was 29º and the height was 55.4 feet.

5.  Man-Tree Comparison

Finally, I photographed a man of known height standing next to the tree.  On the photo I drew and measured lines representing the height of each.  The ratio of the heights of man and tree is the same as the ratio of the lengths of the two lines.
man-line = 1.7 cm; tree-line = 16.8 cm; man-height = 5.75 ft
tree-height = (16.8/1.7) x 5.75 ft = 56 ft
Click on image and look close to see man next to tree.

Results and Discussion

The average height was 58.4 feet, not counting the Shadows results.  The Man-Tree method was the easiest, and probably the most accurate given the conditions.
So there you have it -- tree-measuring -- something to do with your favorite tree while waiting for spring.  And if you aren't yet following a tree and would like to, visit Lucy’s Loose and Leafy Tree Following page to sign up.

Sunday, April 6, 2014

Scenery & Slides along the Big Sur Coast

Driving on charnockitic tonalite -- massive, very hard, and super scenic ...
... especially when the fog clears.
A sunny day along the Big Sur coast brings out smiles ...
... and gorgeous colors in the ocean.
About 29 million years ago, a large piece of Southern California began shifting northwest along various faults (e.g. the famous San Andreas), causing earthquakes, landslides and other “destruction” along the way.  It's shifting very slowly, but it's been doing so for such a long time that it has managed to travel hundreds of miles.  This is an incredible story that I never get tired of pondering.  But it far exceeds my geologic understanding (and perhaps everyone's) so I won’t try to explain further; you can read more via the sources at the end of this post.  Geotripper provides a short account in the first part of  Where the Sierra Nevada Rises from the Sea: Point Reyes National Seashore.
Source
This map shows the results of the crazy geologic history of coastal California -- a puzzling patchwork of rock units.  Click on the image to see details.  Even if you’re not into geologic maps, note the pink unit next to the ocean (green arrow).

The traveling chunk of continental crust is carrying along a large mass of very hard rock with the impressive name of charnockitic tonalite, part of the pink unit indicated on the map.  It resides on the Big Sur coast.  Because the rock is so hard, the slopes are steep (50-65%) and the scenery is spectacular -- perfect for a scenic drive.  And there is one, California State Route 1.  This segment has been open since the 1930s.  When we drove it last month, I was struck by its improbability.
Even though charnockitic tonalite slopes are steep, they're relatively stable compared with other parts of Highway 1.  Landslides are less common, and are mostly smaller rock and debris slides (see p 33 in this PDF).  However ...
McWay slide ca 1983.  Source
... there are occasional zones of weakness, including just north of McWay Falls.  In 1983 the slope gave way, closing Highway 1 for almost a year.

Several factors may have contributed -- vegetation burned off by fire, heavy rain that season, and probably the highway itself.  Whatever the causes, the amount of earth that moved was huge.  The California Department of Transportation had to push eight million cubic yards of it further downhill to stabilize the slope and make a new road bed.
I guess eight million cubic yards is a lot, but when I read the interpretive sign at the end of the McWay Falls Trail, the figure didn’t make much of an impression.  It’s just a really big number.  On the other hand, the photo on the sign really struck me when I looked close:
Zooming in on the interpretive sign.
Looking really close -- oh my!
That’s a phalanx of large bulldozers!  That's what they did day after day for almost a year.

Thanks to the slide and CalTrans, a lot of debris was moved to within reach of the ocean, and rains periodically add more.  The debris plumes are obvious.  A current carries the material south, and has deposited sand in what used to be a water-filled cove with a falls. Now McWay Falls lands on a beach much of the time.  See Geotripper’s Geologic Change Along the Big Sur Coastline: Julia Pfeiffer Burns State Park.
Debris plume at base of slide (yellowish-green water).

There was hope that plants could help stabilize the slopes near the highway, and various revegetation schemes were tried.  Results were disappointing:
“The McWay landslide project contained elements of the worst case site conditions for stabilizing surface soil erosion, establishing vegetation and controlling weedy exotic plants. ... The primary lesson of the study is that vegetation alone cannot stabilize materials on steep slopes.  ...  It is not cost effective to invest in and implement a native perennial revegetation plan on unstable sites prone to large-scale land movement.  The unstable sites are cost effectively treated with an annual native vegetative cover along with sterile straw or other surface erosion control methods.”  [after first consolidating and stabilizing slopes] 
“The primary conclusion of this report is that re-vegetation and erosion control work conducted on Highway One may offset and mitigate highway related erosion impacts but cannot be expected to deal with natural erosion” Source

Now 31 years later, the slide is somewhat vegetated but still obvious:
McWay Slide in 2014; note barren upper and lower slopes, and the obvious debris plume.
Google Earth view, 2012; click on image to see more detail.

Sources (in addition to links in post)

Cal Poly Pomona Geology Club Spring 2003.  Field Trip Big Sur (PDF).

UCSC.  Geology of the Point Sur-Lopez Point region, Coast Ranges, California (PDF).

SFSU.  Geology of the California Central Coast (PDF).

Watershed Institute, CSUMB.  2000.  Big Sur Coast Highway One erosion and revegetation management (PDF).

Sunday, March 30, 2014

Dreaming of Online Plants

This lupine in Santa Barbara County has been immortalized as iNat Observation 569966.
What if you were a nature geek planning a vacation, and you found a website about the wildflowers of your destination area with photos, dates of observation, places to see them, and even an app for identification?  How cool would that be?!!
Plants of Santa Barbara County, California; arrow points to location of lupine in top photo.
[Click on all images to view details.]
It would be very cool, and in fact such websites are already out there.  Problem is -- the data are sparse, even in California where I went a few weeks ago.  But there are things we can do to change that.

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I used to dream of compiling a book about the native plants of my home territory, with keys and photos for identification.  But devoting huge amounts of time, effort, and attention to detail before seeing any results isn't for me, and lining up and financing publication always seemed daunting.  However now that I'm living in the digital age, the dream has been resurrected.  Online I can “publish” as I go, instead of waiting until I’ve addressed many hundreds of species.  Others can help by contributing observations.  And it will cost almost nothing.  Sounds doable!

In fact, I’ve already started.  Right now I’m checking out websites and apps (if you have recommendations, I'd love to hear).  I read about iNaturalist several weeks ago in a post at The Dipper Ranch.  It looked promising so I gave it a test during my vacation on the Central California Coast.  Before I left home, I searched for plant observations in Santa Barbara County (above).  Then I entered my own from a hike on the Point Sal Road.
We used to drive the family station wagon to Point Sal on this road!
Point Sal beach from near "the pass" -- about halfway to the beach (5 miles one-way).
First I created an iNaturalist account.  I was able to sign in with my Google account; Twitter, Facebook and others work too.  Next I entered observations -- plant name, location, date, photos, description and more.  It all seemed intuitive and easy.
Fuschia-flowered gooseberry, Ribes speciosum (iNat observation).
Description:  "Low shrub growing with Toxicodendron diversilobum on slope just below road."
Identification can be to any level -- family, genus, species, common name, or even just “plant”.  Accepted names are available from drop-down lists, and there’s a box to check if you’d like some help:
Request for identification assistance, highlighted in yellow (iNat Observation).
Location can be as precise as you like.  You can enter coordinates or click on a Google Map.  For this outing, I mapped all observations to a single location about halfway between the trailhead and “the pass” (they were all north of the pass).
The "trail" to Point Sal beach is a narrow winding old road that's now closed to vehicles.
Photos can be uploaded directly, or you can link to other image hosting sites.  You can include multiple images per observation.
Flowers of poison oak, Toxicodendron diversilobum (iNat observation) ...
... and the despised leaves that cause itching and inflammation in most people.
It was easy to enter multiple observations for a single location with the Copy option.  It’s also possible to Batch-process and Import.  By the time I was done, I had added six observations from California to my single observation from Wyoming (the tree I’m following):
My first iNaturalist observations.

Searching

iNaturalist has good search tools for investigating the natural history of an area.  You can use text fields or a map.  Results are displayed as photos, text, or even hierarchically for those who are taxonomically-inclined.
iNaturalist search fields.

Projects

One thing that really excites me is the Projects option.  “Projects are a way to pool your observations with other people on iNat. Whether you're interested in starting a citizen science project or just keeping tabs on the birds in a nearby park with your local birding club, Projects are the way to go.”  Here's a nice example -- the More Mesa Natural Resources project near Santa Barbara, California.
More Mesa home page.
Output from the More Mesa project.  It currently includes 369 observations.

I hope there will be a "Plants of the Laramie Mountains" project soon, where anyone can share their observations.  We'll be able to see what's blooming, what's new, and of course debate identification -- a popular sport among botanists.  Folks new to the area can get to know our local plants, once we’ve added enough observations.
The only iNat plant observation in southeast Wyoming currently is my cottonwood (green arrow).
This caveat applies not just to iNaturalist but to citizen science in general -- scientific research conducted by amateur or nonprofessional scientists as well as professionals, often by crowdsourcing.  The usefulness of citizen science projects depends on participation; many are still in their infancy so data are sparse.  But surely at least some will grow to maturity, for why wouldn't naturalists want to contribute?  It's great to be able to share, debate, modify and continually update information ... to “record what [we] see in nature, meet other nature lovers, and learn about the natural world” (iNaturalist).

Here's a video featuring one such nature lover, Sonny Riddell, who demonstrates moth-collecting and citizen science.  I’m very glad to have “met” Sonny.  He's a great role model. His enthusiasm is contagious, and he reminds me how much fun it is when we really focus on what we enjoy.  You can learn more at SPRING AND MOTHS WHEN YOU ARE EIGHT YEARS OLD

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How about you?  Do you use iNaturalist?  What do you think of it?