27) Igneous Rocks Overview

Bowen's Reaction Series

In addition to the "3 Utilizations" of the Bowen Reaction Series listed and described in the videos of the three previous days, understanding the Bowen Reaction Series helps you understand why - in igneous rocks - certain minerals "associate" with others, while other minerals don't usually "associate" with each other.

For instance, because of the higher temperatures associated with Ultramafic and Mafic rocks, Quartz and Muscovite are not usually found with those rock types, as they are still molten while the ultramafic/mafic minerals are crystallizing and "squeezing out" the remaining liquids.  [Or if the mafics were erupted in a setting with a paucity of "free quartz", e.g., the Mid-Atlantic Ridge or the Hawaiian Hot Spot" or where the crust is thin, allowing the mafic magmas to "quickly" reach the surface, e.g., a Continental Rift Zone.]

Likewise, it is not "normal" for there to be Olivine in a Granite (or similar Felsic rock).  The Geology Department chair at my undergraduate college had a sizeable chunk of Olivine Granite that he had collected from the Big Bend region of Texas.  Most likely, the semi-molten granite had "plucked" the olivine granites from an adjacent peridotite, preserving them as "micro-xenoliths" or xenocrysts.

Geology: Bowen's Reaction Series

To follow up on the posts of the last two days, there are 3 "utilizations" of the Bowen Reaction Series.  They are:

1.) The classic prediction of the order-of-crystallization of major silicate minerals in a cooling magma (or lava).

2.) Order-of-melting during partial melting (increasing temperatures).

3.) During the "downward" progression-of-solidification as shown in the diagram, the internal structures of the silica minerals are becoming more "organized" and more stable.  In other words, at the "top" of the diagram, Olivine, Pyroxene, and Calcium Plagioclase, the "lesser" internal organization makes these minerals more-susceptible to Chemical Weathering than Muscovite Mica and Quartz (at the "bottom").

This is cited as one reason for the propensity of exposed granites over gabbros and peridotites and the primary reason for quartz being the dominant type of sands on the beaches of the world.

14) Bowen's Reaction Series

Yesterday's post was an informal Part 1 of this short series of videos on the Bowen Reaction Series. 

The Bowen Reaction Series has three "utilizations". 

1.)  Predicting the order-of-crystallization of minerals in a cooling magma or lava. 

2.) When the order-of-crystallization is reversed, it becomes an order-of-melting (or partial melting) of a solidified magma.  [This was hinted at in yesterday's video, though not explicitly explained.]  That being the case, as Quartz is the "last" mineral to solidify, it becomes the "first" mineral to melt as the temperature increases.

This is what occurs during episodes of partial melting - if the "proper minerals" are present.  As the temperature increases, and as time duration, pressure and fluid contents "permit", Quartz, Muscovite, K Feldspar, Biotite, Sodium Plagioclase, ... progressively melt.  [Pressure and Fluid Content affect the Melting Point.]

Figure 1.

In the Figure 1 "scenario", assuming that a Gabbro is the "starting point", the "end product" is a function of the conditions listed above (time-duration, temperature, pressure, and fluid content).

[The third "utilization" of the Bowen Reaction Series will be presented tomorrow.]

Earth Parts #29 - Bowen's Reaction Series

The image below is used for educational purposes.  (As I don't have a good hand sample of a Diorite - as an example of an Intermediate Igneous Rock - I had to use a Porphyritic Andesite, from the "Campus Andesite", a shallow Eocene intrusion underlying the University of Texas-El Paso campus.)

Figure 1.

Below (Figures 2 and 3) are descriptions of the Mafic and Felsic "End Members" of this range. 

 Figure 2.  Gabbro - unknown source.

Figure 3.  Granite - Pennsylvanian Elberton Granite.

Figure 4.  Ultramafic Mantle Xenolith - Quaternary Maar eruption.

At least two more Bowen Reaction Series posts are planned for the coming days.  Repetition helps enforce memorization, while different articulations may induce different insights.

The History of Geology

Geology: Felsic vs Mafic

Figure 1.

16) Olivine Pyroxene and Amphibole

FerroMagnesian minerals from the "top" of the Bowen Reaction Series.

Sand Atlas webpage on Peridotite.

15) Feldspars and Quartz

Felsic Minerals from the "bottom" of the Bowen Reaction Series.

The Pleistocene Ice Ages [Original Post Date: 3/26/06]

[Reposted and somewhat revised from a retired version of this blog.]

Currently, as defined by Geologists, we live in the Cenozoic Era, Quaternary Period, and Holocene Epoch (since the last 10,000 years or so).

The previous epoch was the Pleistocene, which lasted from approximately 2 million years ago to 10,000 years ago. Before the Pleistocene Epoch was the Pliocene Epoch, which lasted from approximately 5 million to 2 million years ago.

Most people have a vision of the Pleistocene climate as being a single large Ice Age when in reality there were several periods of glacial advance, separated by shorter interglacial periods, some of which were as warm or warmer than today's climate. The primary attributed reasons for the fluctuations were variations in Earth orbit, Earth axial tilt, and variations in solar output. Some of these fluctuations exaggerate each other, while others moderate each other. Random events such as large volcanic eruptions may play a role, also. Evidence suggests that global cooling began in the latter part of the Pliocene.

Some authors suggest that the emergence of the Isthmus of Panama (above Sea Level) during the Late Pliocene played a role in the cooling of the climate. Prior to the emergence of the isthmus, there was a narrow seaway that allowed the movement of warm waters from the Caribbean into the East Pacific. The closure of this seaway altered oceanic currents, while opening a land bridge that allowed the migrations of mammals between North and South America.

There have been previous periods of global glaciation, but those were before humans. Oxygen-18 isotopic data is one type of proxy data used to reconstruct paleoclimate history, including the Pleistocene data listed here in Wikipedia.

From youngest to oldest, as identified in North America, the Pleistocene glacial stages were:

Wisconsinan Glacial Stage
Sangamonian Interglacial
Illinoian Glacial Stage
Yarmouthian Interglacial
Kansan Glacial Stage
Aftonian Interglacial
Nebraskan Glacial Stage
Pre-Nebraskan

After each glacial stage, the interglacial represented a period of natural global warming, a period of rebound. Since the end of the Wisconsinan Glacial Stage approximately 10,000 years ago, there have been several alternating shorter periods of warming and cooling.

Previous ice ages include:

• A poorly-documented, possible ice age from 2.7 to 2.3 billion years ago, during the early Proterozoic Era.
• The earliest, well-documented ice age was during the late Proterozoic Era, from approximately 800 million to 600 million years ago.
• Late Ordovician Period 460 million to 430 million years ago.
• Late Carboniferous Period to Early Permian Period 350 million years to 260 million years ago.

From this above-linked Wikipedia article:  [Remember, unfortunately, not everyone that posts or edits on Wikipedia is of "good faith".  It is best to try to cross-reference with other sources.]

..."The present ice age began 40 million years ago with the growth of an ice sheet in Antarctica but intensified during the Pleistocene (starting around 3 million years ago) with the spread of ice sheets in the Northern Hemisphere. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000 and 100,000-year time scales. The last glacial period ended about 10,000 years ago."

This Wikipedia link shows temperature trends during the last 5 million years.

The Pleistocene Epoch is the recent geologic past. If there were repeated periods of natural global cooling and global warming then, why are people so convinced that any and all unusual changes and variations are triggered by humans?

6 Factors Affecting India's Climate | Geography, Climatology

The factors influencing India's climate are largely "universal", with the exception of some local effects (height of mountains, size, and shape of the landmass, and others).  

In other words, it could be a good starting point for a general understanding of longterm climate processes on other continents.

Types of Clouds - Cirrus, Cumulus, Stratus, Nimbus | UPSC IAS Geography

The subject of clouds was previously visited in late January 2020.

Hygroscopic Condensation Nuclei | Cloud, Rain, Atmosphere

A little more on Condensation Nuclei:

1.) Link

2.) Link (contains a number of informal definitions, some of which may be questionable.)

3.) Link from Penn State Univ.

4.) Link from Sciencing

5.) Link from the viewpoint of the Chemistry of Water.

[As always, taking notes facilitates memorization and learning.]

Just a Reminder:

The postings here are intended for educational and informational purposes.  I may not agree with every video utterance or posted link.

It is up to you to listen, learn, and practice the cross-referencing of different sources until you learn which ones are the most reliable.

Keep checking back, as refinements to posts are ongoing.

Keep an open mind as Science has a "Never-Ending Learning Curve".

I do plan on posting more original content, but that requires "homework" during a time of personal challenges.

Factors Affecting the Movement of Ocean Water - Geography UPSC IAS

Movements of Ocean Water - Chapter 14 Geography NCERT Class 11

Water in the Atmosphere - Chapter 11 Geography NCERT Class 11

Aside from promoting a better understanding of the complexities of the atmosphere, water is vitally important to the processes of Weathering, Erosion, and shaping of the land surface.

How soil is formed from rocks - Soil formation | Pedogenesis

A short video on Soil Formation (aka Pedogenesis).

Geomorphic Processes - Chapter 6 Geography NCERT Class 11

Geomorphic Processes - Geomorphology | Shaping the Earth's crust

Distribution of Oceans and Continents - Chapter 4 Geography NCERT Class 11

Day 4.

Continental Drift Theory - Alfred Wegener | Pangea | Gondwanaland

Interior of the Earth - Chapter 3 Geography NCERT Class 11

Day 3.

A few terms to remember:

Exogenic Processes - External (surface and near-surface) processes. 

Endogenic Processes - Internal (subsurface) processes.

[More to be added.]

Why Geology?

Dropped in here randomly.  Each person has their own story.

For my own story, as many kids are, I was interested in dinosaurs and other big critters and volcanoes, though none of these were present in the immediate area in which I grew up, on the Georgia Piedmont, Northeast of Atlanta.  

Fortunately, my parents both enjoyed being outdoors, whether working in the family garden, tromping through the woods, panning for gold, taking nature hikes, pointing out interesting plants, visiting museums, ...

Though they were not perfect, they were ahead of their time in some ways, compared to other folks.  We were not allowed to through any trash out of the car windows nor into our creek.  When Japanese Beetles became a scourge in the early 1970s, they resisted using insecticides in the garden out of concern for the honey bees, so when Japanese Beetle traps became available, those were deployed instead.

My Dad had taken a Geology class while at Georgia Tech in the middle 1930s, so he had a passing interest in it. (About 8 years after my Dad's passing, my Mom spent her 70th birthday - with a pacemaker - leading a bunch of Cub Scouts on a Nature Hike.)

A couple of important turnings points helped me keep focused upon Geology.  In the 3rd grade, our teacher told us that her husband's road crew had found some Mastodon teeth at a construction site in Florida and he had brought a couple of them home.  As she only lived a block from the school, we were able to secure permission for small groups to walk to her home to see the teeth in their garage (I think this was about 1961 or 1962).

I reasoned (to myself) that if extinct elephants were "running around in Florida, they must have been in Georgia, too".

The second turning point was at the end of my Junior year when selecting my Senior year classes.  When presented with the choices of Physics and Geology, I knew Geology had to be easier than Physics and I had my prior interests to fall back upon.  From the moment I entered college in late 1972, I was always a Geology major, never anything else.

[I am planning on posting more videos in March about Geology as a career.] 

The Origin and Evolution of Earth - Chapter 2 Geography NCERT Class 11

Day 2.

[As my personal schedule permits, I hope to add some highlight notes.]

What are Foehn Winds?

Foehn Winds (or Föhn winds) are locally-strong examples of cross-mountain winds (in mountainous areas) that cause warming and drying of descending air on the lee (leeward)  side of the mountain.  In some areas, there are local names, such as "Chinook Winds", for these winds that are a component of the Rain Shadow Effect.

In this particular post, there is a video on the types of rainfall and within the video, the Rain Shadow Effect is explained at approximately 5:19 in the video.   

In the linear mountain ranges of the North American West Coast (including Canada and Alaska), when the prevailing winds bring Pacific moist air inland, the Orographic Effect occurs as the air moves upslope and chills along the western mountain slopes, triggering precipitation.

Once the winds cross the ridgelines and start to descend the eastern, leeward slopes, the winds become warmer, drier, and faster (due to gravity), producing the Rain Shadow Effect and when particularly strong, the Foehn (Chinook) Winds.

There are times when temporary conditions "reverse" these prevailing directions.  When the sub-tropical Northern Jet Stream is in a "non-wavy" shape, inland High-Pressure Systems "stalled" in the warm Western Interior produce winds that blow westward towards the Pacific Ocean.

As these winds blow to the west and southwest, when they descend the western slopes of the Sierra Nevada and the Pacific Coast Ranges, they "reverse" the "normal" West-to-East Rain Shadow Effect.  When these winds are funneled through mountain passes, their speeds further increase due to the "Venturi Effect".  These are the yearly "Santa Ana winds" or "El Diablo winds" that dry the seasonal vegetation and help spread wildfires.

Geography as a discipline - Chapter 1 Geography NCERT Class 11

Shall we have a few days of Geography lessons?  (We shall, in the interest of "keeping it fresh" and learning something different.)

Physical Geography has quite a bit of overlap with Physical Geology, thus my interest in both.

Informal Geography Series - Introduction

I encountered this lecturer, Amit Sengupta, recently.  In the following days (the time frame is not yet finalized), I will be posting more of his videos, interspersed with other videos and my posts, as time allows.  For the sake of an informal "continuing education", I would suggest subscribing to his YouTube channel.  Here is his website.  [He seems to cover a wide range of subjects.] 

I will revisit and edit this post to include prior and recently-posted Geography lectures, as I have done with the informal Weather "series".  (Hey, it's all Earth Science-related.) 

Here is a little more info on the quasi-resurrection of this blog and my other one.  And a little more personal background in this post.

What is ENSO, El Niño, La Niña, Southern Oscillation, Walker Circulation...

Route 66 Road Trip Stops in Oklahoma

Just a reminder that on my other blog, there are several "Through My Lens" YouTube videos on the historic U.S. Hwy 66.  (I will list them later.)

This particular one is close to my heart as my first wife, Marla, was from NW Oklahoma and over the years, we made several trips to and through the state, as well as other trips along I-40 between Georgia and Arizona (as it is usually cooler in the summer than I-10).  On my first 2015 Arizona trip, I left some of her ashes at the edge of an old family farm in Ellis County.

El Niño Impacts: The Good, the Bad and the Ugly | California Academy of ...

For several reasons, what happens in the Pacific Ocean has influences on North and South America and the Atlantic Ocean that we probably don't yet fully understand.

Among these:

1). Oceans store a great deal of heat (and release it gradually).

2). The Pacific Ocean is the largest of the Earth's oceans.

3).  Do we fully know the effects of the submarine volcanoes and rift zones in the Pacific Ocean, vis-à-vis El Niño/La Niña?  Probably not.

4). All of the Jet Streams (Northern and Southern) "blow" from West to East.

California Is Sinking — and Now Could Flood | KQED Newsroom

As California's weather (and climate, over the long term) is influenced by its close proximity to the Pacific Ocean, a better understanding of El Niño/La Niña Cycles and California's climate history, would be useful in assessing the wisdom of some of the past decisions we have made, in regard to agriculture, water, and improved fire prevention tactics, e.g., reduction of fuel loads. 

As covered in the video, this does not bode well for damage to roads, bridges, canals, near-surface pipelines, powerline support structures, ...

Bushfires and exceptional heat: what's driving our weather right now?

Understanding the Madden–Julian Oscillation (MJO)

Madden-Julian Oscillation is another new concept to which I have been introduced. 

Tropical Cyclone, Hurricane, Storm Formation - Geography of UPSC, IAS, C...

While on the subject of Weather Processes.

Different Types of Rainfall - Convectional, Orographic, Cyclonic Rainfal...

All three of these processes are mechanisms by which moist air masses are uplifted and chilled, with the chilling process triggering condensation and precipitation.

Convectional Lifting - Thermal Convection provides the uplift, explained near the beginning of the video.  (Note the textbook typo.)

Orographic Lifting - Interaction between moist air masses and mountains provides the uplift on the Windward side.  The Rain Shadow Effect is explained beginning at approximately 5:19 in the video.  (Recall that the Rain Shadow Effect is the primary "cause" of the four North American Deserts.)

Cyclonic Lifting - Interaction between dry Cold Air Masses and moist Warm Air Masses is explained at approximately 6:37 in the video.

Other considerations - heat moves towards cool areas

Understanding the Southern Annular Mode (SAM)

Southern Annular Mode (SAM) is something that I just encountered. 

Indian Ocean Dipole

Understanding the Indian Ocean Dipole

The Indian Ocean Dipole is something that I was only recently acquainted with.

Extraordinary animation reveals ocean’s role in El Niños

Subtropical high, Subpolar low, Easterlies, Westerlies | Atmospheric cir...

Understanding ENSO

Different Types of Rainfall - Convectional, Orographic, Cyclonic Rainfal...