geology of national parks: part 2, glacier np and the canadian … · 2017-04-21 · geology of...
TRANSCRIPT
Geology of National Parks: Part 2, Glacier NP and the
Canadian Rockies 1) Principle of Superposition 2) Milankovitch Cycles and Ice Ages
1.
The Principle of Superposition: A sedimentary rock layer in an undisturbed sequence is younger than the one
beneath it and older than the one above it.
Disturbed area exceptions: • Overthrust faults
(Lewis in GNP) • Reverse faults • Overturned folds • Accretion, terrane
creation • Igneous intrusion
2.
Presenter
Presentation Notes
See also https://en.wikipedia.org/wiki/Law_of_superposition
Thrust fault
3.
Presenter
Presentation Notes
Thrust fault
4.
Presenter
Presentation Notes
Lewis Overthrust Fault where 2 mile thick sequence of Belt Supergroup Precambrian 1+ BYA rocks goes over Cret rocks ~100 MY old; as result of Laramide Orogeny (~50-75 MYA) forces and faulting, Belt slipped ~35-50 miles east over top of ~100 MY old rocks - NOTE Pcamb is >542 MY and Cret is 146 – 66 MY; actual Belt Supergroup from 1-1.5 BY and Cret units are in 100 MY range
5.
Presenter
Presentation Notes
From DVD
6.
Nappe
Presenter
Presentation Notes
- “Klippe” is isolated piece at front of over-thrust slab; autochthon is piece below, allochthon is over-thrust slab ex. Chief Mountain in NE corner of park - “nappe” > a sheet of rock that has moved sideways over neighboring strata as a result of an overthrust or folding.
Graphic and Picture from http://formontana.net/chief.html 7.
Presenter
Presentation Notes
Chief Mtn. “klippe”; graphic and non-DVD pic of Chief Mtn. from http://formontana.net/chief.html Mtn ~1500’ - NOTE rocks under thrust fault are only 80 MY old while old rocks above are 1+BY Pc rox
Reverse Fault
8.
Reverse fault as viewed from a well log perspective
9.
Presenter
Presentation Notes
From dfiles.com
Overturned Fold
10.
Presenter
Presentation Notes
Pinterest.com; overturned folds
11.
Presenter
Presentation Notes
From: Okla. State Univ.
12.
Presenter
Presentation Notes
From: reddit/geology.com (top) and regentsearth.com
Accretion 13.
Presenter
Presentation Notes
Accreted “old island arc” could be older than continental land it rides over; from Google images
Igneous Intrusions
14
Presenter
Presentation Notes
Photo from Matthew Thirlwall, Twitter pics.
file:///Volumes/TOSHIBA/Geol%20of%20NPs%20lecture%20spring%202017%20cont/glacier-animation.html
Rapid loss of glaciers in Glacier
National Park (U.S.)
15.
Presenter
Presentation Notes
NOTE that this was done in 2003 and a lot has changed since then; I only show this to appreciate the speed with which the GNP glaciers had receded to that time > future in this video probably not too accurate
Milankovitch cycles are cyclical changes in the Earth’s orbit that can explain the onset and ending of ice ages.
http://www.universetoday.com/39012/milankovitch-cycle/
16.
Presenter
Presentation Notes
Remember from DVD about obliquity? And how earth rotation and orientation in the solar system might affect CC? (next) - Below from Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, 841 pp. doi:10.7930/J0Z31WJ2. Second, climate scientists study both natural and human- induced changes in climate. Over the last century, scientists have learned a great deal about what drives Earth’s ice ages. Scientific understanding of what are called the Milankovitch cycles (cyclical changes in the Earth’s orbit that can explain the onset and ending of ice ages) led a few scientists in the 1970s to suggest that the current warm interglacial period might be ending soon, plunging the Earth into a new ice age over the next few centuries. Scientists continue to study this issue today; the latest information suggests that, if the Earth’s climate were being controlled primarily by natural factors, the next cooling cycle would begin sometime in the next 1,500 years. However, humans have so altered the composition of the atmosphere that the next glaciation has now been delayed. - Milutin Milankpvitch, Serbian, wrote this discovery in 1920s
Eccentricity – deviation from a perfect circle (range 0- 1); Earth
range 0.005 – 0.058, mean 0.028 (today at 0.017) – major cycle at 413,000 year and two
minor cycles that together average a 100,000 year cycle
e = 0
e = 0.5
17.
Presenter
Presentation Notes
From NASA - The shape of the Earth's orbit varies in time between nearly circular (low eccentricity of 0.005) and mildly elliptical (high eccentricity of 0.058) with the mean eccentricity of 0.028. The major component of these variations occurs on a period of 413,000 years (eccentricity variation of ±0.012). A number of other terms vary between components 95,000 and 125,000 years (with a beat period 400,000 years), and loosely combine into a 100,000-year cycle (variation of −0.03 to +0.02). The present eccentricity is 0.017. The relative increase in solar irradiation at closest approach to the Sun (perihelion) compared to the irradiation at the furthest distance (aphelion) is slightly larger than four times the eccentricity. For the current orbital eccentricity this amounts to a variation in incoming solar radiation of about 6.8%, while the current difference between perihelion and aphelion is only 3.4% (5.1 million km). Perihelion presently occurs around January 3, while aphelion is around July 4. When the orbit is at its most elliptical, the amount of solar radiation at perihelion will be about 23% more than at aphelion. - From astronomynotes.com the Earth's orbit is elliptical and that it gets closest in early January. With an orbit eccentricity of 0.0167, Earth receives about 7% more solar energy in early January than at its aphelion point in early July. The Earth's orbit changes eccentricity on cycles of about 100,000 and about 400,000 years. At greatest eccentricity, the Earth can receive over 20% more solar energy at perihelion than at aphelion.
18.
Presenter
Presentation Notes
Note both axial tilt (obliquity) and precession cone; The Earth is not a perfect sphere but an oblate spheroid,
Obliquity (Axial tilt) Range of
Earth’s axial tilt from 22.1°
– 24.5°; currently at
~23.4°; 41,000 year
cycle
19.
Presenter
Presentation Notes
From DVD, range of tilt; we’re about half way in cycle right now
25°
22° (24 cycles / 1MY)
23.4°
20.
Presenter
Presentation Notes
LEFT SIDE LAST 5 MY; RT. SIDE EXPECTED NEXT 1 MY; note 41,000 cycle
Precession of the Equinoxes - A gradual change in the direction of the Earth's axis (precession), caused by gravitational torques exerted by the Moon and Sun on the spinning, slightly oblate Earth; “Wobbling”; a complete precession of the equinoxes requires cycle of 25,800 years (1° every 72 years).
21.
Presenter
Presentation Notes
Closest description would be “wobble”
https://en.wikipedia.org/wiki/Precession#/media/File:Gyroscope_precession.gif
Axial Precession (or Precession of the Equinoxes)
“..movement of
the rotational axis of an
astronomical body, whereby the axis slowly traces
out a cone.”
22.
Presenter
Presentation Notes
“Recession of the equinoxes” > insert the two extremes of this; closer to the sun as we are now in this cycle leads to warmer weather and worse conditions for glaciers Wiki > Axial precession is the movement of the rotational axis of an astronomical body, whereby the axis slowly traces out a cone. In the case of Earth, this type of precession is also known as the precession of the equinoxes, lunisolar precession, or precession of the equator. Earth goes through one such complete precessional cycle in a period of approximately 26,000 years or 1° every 72 years, during which the positions of stars will slowly change in both equatorial coordinates and ecliptic longitude. Over this cycle, Earth's north axial pole moves from where it is now, within 1° of Polaris, in a circle around the ecliptic pole, with an angular radius of about 23.5°. Another def. in Wiki > change in the orientation of the rotational axis of a rotating body
Eccentricity (orbit) – 413,000 and 100,000 years
Obliquity (tilt) – 41,000 years
Precession (wobble) – 25,770 years
23.
Presenter
Presentation Notes
From NASA Past and future Milankovitch cycles. VSOP allows prediction of past and future orbital parameters with great accuracy. ε is obliquity (axial tilt). e is eccentricity. ϖ is longitude of perihelion. esin(ϖ) is the precession index, which together with obliquity, controls the seasonal cycle of insolation. is the calculated daily-averaged insolation at the top of the atmosphere, on the day of the summer solstice at 65 N latitude. Benthic forams and Vostok ice core show two distinct proxies for past global sea level and temperature, from ocean sediment and Antarctic ice respectively. Vertical gray line is current conditions, at 2 ky A.D.
Graph from NOAA 24.
Presenter
Presentation Notes
Focus on dust, from http://en.wikipedia.org/wiki/File:Vostok_Petit_data.svg ; note that graph starts from right - Graph of CO2 (Green graph), temperature (Blue graph), and dust concentration (Red graph) measured from the Vostok, Antarcticaice core as reported by Petit et al., 1999. Higher dust levels are believed to be caused by cold, dry periods. The Earth's orbital eccentricity, tilt, and precession vary in a pattern over thousands of years. The IPCC notes that Milankovitch cycles drove the ice age cycles; CO2 followed temperature change "with a lag of some hundreds of years" (visible on a graph more zoomed in than this) > NOTE some more recent research notes that this probably not true, rather occurred ~ same time but CO2 evidence in ice lagged because of the time it took to make glacial ice; and that as a feedback amplified temperature change. Among other factors, CO2 is more soluble in colder than in warmer waters.
25.
Presenter
Presentation Notes
Above - Figure 1: Temperature change at Vostok, Antarctica (Petit 2000). The timing of warmer interglacials is highlighted in green; our current interglacial, the Holocene, is the one on the far right of the graph. At https://www.skepticalscience.com/heading-into-new-little-ice-age.htm Below - 800K = mid-Pleistocene Epoch; Source??
NOAA data, graphic from http://www.astronomynotes.com/solarsys/s11.htm 26.
Presenter
Presentation Notes
Note that we see today’s high temps but for CO2 <300 ppm > today’s is ~408 for Feb. which falls on averaged line prepared by NOAA GISS
NOAA March 2017 CO2
complete data from Mauna Loa
Started by C. David Keeling of the Scripps Institution of Oceanography in March of 1958
409
27.
Presenter
Presentation Notes
NOAA April 17, 2017 CO2 complete data from Mauna Loa; current = 409.12; note highest levels usually seen in Apr-June
??*
Last ice age peaked ~20,000 years ago, sea levels about 390’ (120m) lower
Sea levels 13-20’ (4-6m) higher than today with
temps 5-9ºF higher (~2100 prediction)
Reference dates - 4/18/17 409 ppm - IPCC 2014 398 ppm - IPCC 2007 380 ppm - IPCC 2002 360 ppm
IPCC AR5, 2014 28.
Presenter
Presentation Notes
See AR5 draft report ch. 12 for other info; Perhaps most important slide for understanding our fear; From Nat. Acad. Of Sciences for Vostok Ant. From ice core; we have had high temps before parelling CO2 BUT very recent accel. in CO2; temp changes occur over periods of 5-10k years – NOT 100; some speculate we’ll hit 450 ppm by 2100; insert shows reason for concern > actual CO2 emission have been more than IPCC worst case scenario at an accelerating growth rate now at 3.5% per year> where and how will it end? MEGADISASTER?? Will we reach “irreversibility”? I will cover some aspects of climate change that might in fact be irreversible over at least centuries like ocean acidif., sea level rise, glacial melting and changing hydrol. Cycle >> difference now, 6B people! > 3MY ago in mid-Pliocene era climate was as we expect by 2100 so it is unbiased basis for comparison BUT no CO2 or population; 2000-09 hottest decade since record keeping began 130 years ago; CO2 levels highest in 650,000 years of direct and surrogate records _ NOTE that temp on this graphic given for Antarctica so that’s why reversed on scale and all well below zero
NOAA 29.
Presenter
Presentation Notes
> note rt side longer record and shows how radiance been going down for last 35 years while temps skyrocket; “The sun's energy fluctuates on a cycle that's about 11 years long (see NOAA graph to left) . The energy changes by about 0.1% on each cycle. If the Earth's temperature was controlled mainly by the sun, then it should have cooled between 2000 and 2008. ” Rt - From Skeptical Science at https://www.skepticalscience.com/solar-activity-sunspots-global-warming.htm - Figure 1: Annual global temperature change (thin light red) with 11 year moving average of temperature (thick dark red). Temperature from NASA GISS. Annual Total Solar Irradiance (thin light blue) with 11 year moving average of TSI (thick dark blue). TSI from 1880 to 1978 from Krivova et al 2007. TSI from 1979 to 2015 from PMOD (see the PMOD index page for data updates).
Presenter
Presentation Notes
Left NOAA used in my CC presentstion; rt from https://www.skepticalscience.com/solar-activity-sunspots-global-warming.htm