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Here comes the Sun

This post cross-posted at Highly Allochthonous.

The Earth’s axis has a 23.44o obliquity or tilt to it. As the Earth revolves around the Sun over the course of a year, the axial tilt means that different parts of the Earth’s surface receive direct sunlight at different times of the year. And it’s this receipt of varying intensities of solar radiation that drives temperature differences, and hence seasonality.

Today is a solstice, illustrated by the image on the far right below. Today is the day of the year when the Northern Hemisphere is tilted farthest away from the sun and the Southern Hemisphere is tilted most towards the sun. For those of us in the Northern Hemisphere, it’s our shortest day of the year and the sun never gets very high in the sky, even at noon. In fact, the word solstice has a Latin origin in the word solstitium, where “sol” means sun and “stitium” means stoppage. and for several days around the solstice this noontime elevation appears to be the same – hence the stoppage. Today, the noontime sun appears directly overhead along the Tropic of Capricorn, 23.44o S.

305px-North_season.jpgFigure 1. Earth at the solstices and equinoxes, as seen from the north. Source: Wikimedia.

The precise moment of the solstice occurs at 17:47 UTC (12:47 pm Eastern Standard Time). We’ll have another solstice (image on far left) on 21 June 2010 at 11:28 UTC ( 7:28 am Eastern Daylight Time). Over the course of the Earth’s trip around the Sun there will be two moments when everybody is getting their fair share of sunlight – the equinoxes. In 2010, they’ll occur on 20 March 2010 at 17:32 UTC and 23 September 3:09 UTC (22 September 11:09 pm EDT).

Earth’s tilt also varies over geologic time. It has a ~41-thousand year cycle, and right now we’re at about the middle of the range in variation of axial tilt. As tilt increases, seasonal contrasts over much of the world increase, but it is decreased axial tilt is tied with the onset of continental glaciation. That’s because at high latitudes, when tilt is low, summers are even cooler, and more snow persists through the summer. That surviving snow forms the nucleus of glacial ice caps. We’re currently on the decreasing limb of the obliquity cycle, but based on past occurrence of continental glaciations, the onset of another one is going to require not just less obliquity, but also the right eccentricty and precession in the Earth’s orbital parameters and controlling greenhouse gas emissions.

axialtilt-big.png
Figure 2: Last seen at Clastic Detritus in 2007, original created by Slumbering Lungfish.

My picks of the September literature

Haggerty, Roy; Martí, Eugènia; Argerich, Alba; von Schiller, Daniel; Grimm, Nancy B. 2009. Resazurin as a “smart” tracer for quantifying metabolically active transient storage in stream ecosystems J. Geophys. Res., Vol. 114, No. G3, G03014
(Roy will be talking about this work in our session at the GSA Annual Meeting next month.)

Harman, C. J.; Sivapalan, M.; Kumar, P. 2009. Power law catchment-scale recessions arising from heterogeneous linear small-scale dynamics Water Resour. Res., Vol. 45, No. 9, W09404
(Ooh, this sounds really cool. I’ve been interested in heterogeneity in watersheds for a while, and this looks like an interesting take on the topic.)

Moussa, Roger 2009. Definition of new equivalent indices of Horton-Strahler ratios for the derivation of the Geomorphological Instantaneous Unit Hydrograph Water Resour. Res., Vol. 45, No. 9, W09406

Philip Brunner, Craig T. Simmons, Peter G. Cook
Spatial and temporal aspects of the transition from connection to disconnection between rivers, lakes and groundwater
Journal of Hydrology, 376: 159-169

Astrid Lambrecht, Christoph Mayer, 2009, Temporal variability of the non-steady contribution from glaciers to water discharge in western Austria, Journal of Hydrology, 376: 353-361.
(Relevant to my Mt. Hood work.)

I. P. Holman, M. Rivas-Casado, N. J. K. Howden, J. P. Bloomfield, A. T. Williams. 2009. Linking North Atlantic ocean-atmosphere teleconnection patterns and hydrogeological responses in temperate groundwater systems. Hydrologic Processes. 23(21): 3123-3126.
(The invited commentaries (like this one) in HydroPro are almost always worth a read to see what leading hydrologic thinkers are thinking about.)

Tiwari, V. M.; Wahr, J.; Swenson, S. 2009. Dwindling groundwater resources in northern India, from satellite gravity observations Geophys. Res. Lett., Vol. 36, No. 18, L18401
(This is at least the third paper I’ve seen on this topic in the past month. It is big big news.)

More new papers I'm itching to read

Godsey, S.E., J.W. Kirchner, and D.W. Clow, 2009. Concentration-discharge relationships reflect chemostatic characteristics of US catchments, Hydrological Processes 23 (13): 1844-1864.

Tetzlaff, D., J. Seibert, and C. Soulsby. 2009. Inter-catchment comparison to assess the influence of topography and soils on catchment transit times in a geomorphic province; the Cairngorm mountains, Scotland. Hydrological Processes 23 (13): 1874-1886.

Lyon, S.W., S.L.E. Desilets, and P.A. Troch. 2009. A tale of two isotopes: differences in hydrograph separation for a runoff event when using delta-D versus delta-18O. Hydrological Processes 23 (14): 2095-2101.

Bloomfield, J.P., D.J. Allen, and K.J. Griffiths. 2009. Examining geological controls on baseflow index (BFI) using regression analysis: An illustration from the Thames Basin, UK, Journal of Hydrology, 373: 164-176.

Pascal Goderniaux, Serge Brouyère, Hayley J. Fowler, Stephen Blenkinsop, René Therrien, Philippe Orban, Alain Dassargues. 2009. Large scale surface–subsurface hydrological model to assess climate change impacts on groundwater reserves, Journal of Hydrology, 373: 122-138

The Geologist's 100 Things List

I haven’t posted in a while, but I feel a few posts getting ready to ooze out over the next few weeks. But in order to get back into the swing of things, I’m going to indulge in some lightweight posting. Ages ago by internet standards (but less than an eye blink in geologic time), a meme circulated amongst geo bloggers. It was a list of 100 things that all geologists should see.

Here’s how I stack up:

Thing’s I’ve done are in bold, with partial credit in italics.

1. See an erupting volcano. [A wisp of steam from Mt. St. Helens viewed through an airplane window doesn’t really count does it?]
2. See a glacier. [New Zealand, Iceland, Oregon, Ellesmere Island]
3. See an active geyser such as those in Yellowstone, New Zealand or the type locality of Iceland. [all three actually]
4. Visit the Cretaceous/Tertiary (KT) Boundary. Possible locations include Gubbio, Italy, Stevns Klint, Denmark, the Red Deer River Valley near Drumheller, Alberta.
5. Observe (from a safe distance) a river whose discharge is above bankful stage. [The Mississippi River in 1993 and 1997 and many many others. It’s an occupational hazard.]
6. Explore a limestone cave. Try Carlsbad Caverns in New Mexico, Lehman Caves in Great Basin National Park, or the caves of Kentucky or TAG (Tennessee, Alabama, and Georgia). [Carlsbad for a big one and Mystery Cave for one local to the karst area where I grew up]
7. Tour an open pit mine, such as those in Butte, Montana, Bingham Canyon, Utah, Summitville, Colorado, Globe or Morenci, Arizona, or Chuquicamata, Chile. [I’ve been to plenty of gravel pits. Do those count?]
8. Explore a subsurface mine. [Colorado, Minnesota]
9. See an ophiolite, such as the ophiolite complex in Oman or the Troodos complex on the Island Cyprus (if on a budget, try the Coast Ranges or Klamath Mountains of California).
10. An anorthosite complex, such as those in Labrador, the Adirondacks, and Niger (there’s some anorthosite in southern California too).
11. A slot canyon. Many of these amazing canyons are less than 3 feet wide and over 100 feet deep. They reside on the Colorado Plateau. Among the best are Antelope Canyon, Brimstone Canyon, Spooky Gulch and the Round Valley Draw. [Alligator Gorge, Flinders Range, Australia]
12. Varves, whether you see the type section in Sweden or examples elsewhere.
13. An exfoliation dome, such as those in the Sierra Nevada. [Yosemite]
14. A layered igneous intrusion, such as the Stillwater complex in Montana or the Skaergaard Complex in Eastern Greenland.
15. Coastlines along the leading and trailing edge of a tectonic plate (check out The Dynamic Earth – The Story of Plate Tectonics – an excellent website).
16. A gingko tree, which is the lone survivor of an ancient group of softwoods that covered much of the Northern Hemisphere in the Mesozoic.
17. Living and fossilized stromatolites (Glacier National Park is a great place to see fossil stromatolites, while Shark Bay in Australia is the place to see living ones)
18. A field of glacial erratics. [Mt. Desert Island, Maine among others]
19. A caldera [Taupo in New Zealand].
20. A sand dune more than 200 feet high [I’ve seen some pretty big ones but I don’t think any have broken 200 ft.]

21. A fjord. [Fjordland, New Zealand.]
22. A recently formed fault scarp. [Assuming ‘recently formed’ stretches to ‘in the last 15 years’, in Greece.]
23. A megabreccia.
24. An actively accreting river delta. [many small tributaries to the Mississippi River]
25. A natural bridge. [Arches National Park]
26. A large sinkhole. [southeastern Minnesota]

27. A glacial outwash plain [Iceland, New Zealand]

28. A sea stack. [Twelve Apostles, Victoria, Australia]
29. A house-sized glacial erratic. [A small house, but Mt. Desert Island, Maine]
30. An underground lake or river. [e.g., in Mystery Cave, Minnesota]
31. The continental divide. [Which continental divide? Nonetheless, I’ve seen several.]
32. Fluorescent and phosphorescent minerals. [At the Smithsonian]
33. Petrified trees. [Ellesmere Island]
34. Lava tubes. [Oregon, New Zealand].
35. The Grand Canyon. All the way down. And back. [Not yet, darn it]
36. Meteor Crater, Arizona, also known as the Barringer Crater, to see an impact crater on a scale that is comprehensible.
37. The Great Barrier Reef, northeastern Australia, to see the largest coral reef in the world.
38. The Bay of Fundy, New Brunswick and Nova Scotia, Canada, to see the highest tides in the world (up to 16m).
39. The Waterpocket Fold, Utah, to see well exposed folds on a massive scale.
40. The Banded Iron Formation, Michigan, to better appreciate the air you breathe.
41. The Snows of Kilimanjaro, Tanzania,
42. Lake Baikal, Siberia, to see the deepest lake in the world (1,620 m) with 20 percent of the Earth’s fresh water.
43. Ayers Rock (known now by the Aboriginal name of Uluru), Australia. This inselberg of nearly vertical Precambrian strata is about 2.5 kilometers long and more than 350 meters high.
44. Devil’s Tower, northeastern Wyoming, to see a classic example of columnar jointing.
45. The Alps.
46. Telescope Peak, in Death Valley National Park. From this spectacular summit you can look down onto the floor of Death Valley – 11,330 feet below.
47. The Li River, China, to see the fantastic tower karst that appears in much Chinese art.
48. The Dalmation Coast of Croatia, to see the original Karst.
49. The Gorge of Bhagirathi, one of the sacred headwaters of the Ganges, in the Indian Himalayas, where the river flows from an ice tunnel beneath the Gangatori Glacier into a deep gorge.
50. The Goosenecks of the San Juan River, Utah, an impressive series of entrenched meanders.
51. Shiprock, New Mexico, to see a large volcanic neck.
52. Land’s End, Cornwall, Great Britain, for fractured granites that have feldspar crystals bigger than your fist.
53. Tierra del Fuego, Chile and Argentina, to see the Straights of Magellan and the southernmost tip of South America.
54. Mount St. Helens, Washington, to see the results of recent explosive volcanism.
55. The Giant’s Causeway and the Antrim Plateau, Northern Ireland, to see polygonally fractured basaltic flows. [I’ve seen plenty of other polygonally fractured basalt flows though…]
56. The Great Rift Valley in Africa.
57. The Matterhorn, along the Swiss/Italian border, to see the classic “horn”.
58. The Carolina Bays, along the Carolinian and Georgian coastal plain
59. The Mima Mounds near Olympia, Washington
60. Siccar Point, Berwickshire, Scotland, where James Hutton (the “father” of modern geology) observed the classic unconformity.
61. The moving rocks of Racetrack Playa in Death Valley
62. Yosemite Valley
63. Landscape Arch (or Delicate Arch) in Utah
64. The Burgess Shale in British Columbia
65. The Channeled Scablands of central Washington
66. Bryce Canyon
67. Grand Prismatic Spring at Yellowstone
68. Monument Valley
69. The San Andreas fault
70. The dinosaur footprints in La Rioja, Spain
71. The volcanic landscapes of the Canary Islands
72. The Pyrennees Mountains
73. The Lime Caves at Karamea on the West Coast of New Zealand
74. Denali (an orogeny in progress)
75. A catastrophic mass wasting event [The results at least: some spectacular debris flow tracks on Mt. Hood, seen a few months after they occurred.]
76. The giant crossbeds visible at Zion National Park
77. The black sand beaches in Hawaii (or the green sand-olivine beaches)
78. Barton Springs in Texas [I’ve seen a bunch of other large springs, but not Barton]
79. Hells Canyon in Idaho
80. The Black Canyon of the Gunnison in Colorado
81. The Tunguska Impact site in Siberia
82. Feel an earthquake with a magnitude greater than 5.0.
83. Find dinosaur footprints in situ
84. Find a trilobite (or a dinosaur bone or any other fossil)
85. Find gold, however small the flake
86. Find a meteorite fragment
87. Experience a volcanic ashfall
88. Experience a sandstorm.
89. See a tsunami.
90. Witness a total solar eclipse
91. Witness a tornado firsthand (Important rules of this game).
92. Witness a meteor storm, a term used to describe a particularly intense (1000+ per minute) meteor shower
93. View Saturn and its moons through a respectable telescope.
94. See the Aurora borealis, otherwise known as the northern lights.
95. View a great naked-eye comet, an opportunity which occurs only a few times per century.
96. See a lunar eclipse.
97. View a distant galaxy through a large telescope
98. Experience a hurricane. [Floyd in 1999 in Baltimore]
99. See noctilucent clouds
100. See the green flash

If I counted right, I’ve made it through 36 on the list.