Congratulations, you are standing on the largest rift in the United States. What is a rift?
Lets start with something most people are familiar with; earthquakes. Most people understand subduction, if they don’t quite understand the definition. When one surface area of the outer earth (mantle) slides under the other, the result is often an earthquake. Where it occurs is called a fault line. One of the most famous fault lines in the United States is California’s San Andreas Fault, which is technically a transform fault. Subduction is much more common further north where OR and WA kiss the Pacific Ocean. Usually subduction occurs at the rate of 2-8 cm a year.
Step back for a moment to review some geographical terms we’ll use for the next few minutes. The crust is the outer surface of the earth, about the top 0-2% of its depth, or 5-40 km, depending where you are. That crust and the upper mantle compose the lithosphere, which makes up in parts as much as the upper 10% of the earth. Going deeper, another 40% comprise the deep mantle which takes down to about 2900 km from the surface, and halfway to the center of the earth. After this comes the 25% that is the outer or liquid core (down to about 5100km), followed by the remaining 25%, the inner or solid core. The true center of the earth sits about 6380km from the surface, depending on where you stand.
Where were we, ah, yes, earthquakes. Sudden slips of mere centimeters of the earths crust can result in monstrous earthquakes with catastrophic results.
Which leads us to the principle that for every action….
…there is an equal but opposite reaction.
While not entirely true, it helps set up the next point. For easy figuring, if subduction is the conversion of two tectonic plates, a rift is the pulling apart of the lithosphere of the earth. Since we know the earth is not growing or shrinking, the land must be coming from somewhere. A rift is, in laymen terms, a hole where the land comes up from. Some times, this may be in the form of a volcano.
And since I mentioned it, this area was once rich in volcanic activity. West of here lay the Malpais Lava Flows, which last erupted nearly 5,000 years ago. To the east, the lava fields near Carizozo, additional evidence of the past violent nature of modern-day New Mexico. However, volcanic activity is another way that brings new land to the surface of the earth. The magma also acts a lubricant of sorts, allowing the lithosphere to move apart, and when it does, it does not always do so evenly. Often it creates multiple tears on the crust, similar to crevasses on a glacier in late summer. Eventually, about 29 million years ago, enough of these crevasses connected. Additionally, garbens, which are fault-enclosed basins, dropped several thousand feet lower than adjacent land.
Socorro Mountain Moonrise
Thanks to Allenmabry for the help embedding my first image.
Simultaneously, mountains such as the Magdalena Mountains to the west rose, exacerbating the difference in height. To the east, the San Andreas Mountains further south did likewise. In time, the Rio Salado Sand Dunes have covered the deep rift; much of the area where you currently stand is actually several miles above the peaks of some mountains.
Interestingly enough, as opposed to most rivers that carve canyons, the Rio Grand flowed to the lowest point, and now follows the rift line. But that is a different EC for a different time...
So how do you get credit for the EC? Simple, answer the four below questions based on the above explanation and your critical thinking skills. Email me before posting a find.
1. What do you think are some modern day advantages to the earth rifting?
2. How far under the dunes do you believe the peaks of the mountains to be?
2. What two mountain ranges can you spot from this location (you may need to look at a map, and they are not listed above)?
4. According to the new sign present, this massive geological trench was shaped “millions of years ago when xxxx xxxxx xx xxxx xxxx .”
5. In accordance with revised GSA guidelines, I'm asking for a photo to be included to prevent "armchair" finds. Those without it after 31DEC23 will be deleted. Thank you.
Sorry, as an owner of many earthcaches I have to add this. Please send answers before posting a log. Do not post a picture of the sign. Doing either of these will cause me to delete your log.