Lover's Leap is actually an ancient undersea volcano, formed near the end of the Farallon Plate. Before the infamous San Andreas Fault that we all know about, the entire west coast of North America was an active subduction zone. I'm going to discuss the general terms that went into making Lover's Leap before getting down and dirty about the specifics.
Lets first discus the main types of plates. There are oceanic plates and there are continental plates. Oceanic plates are made up of mafic rocks, meaning they are low in silica (SiO2) and appear dark in color. Oceanic plates are mostly made up of basalt due to the divergent plate boundary creating new land. I'll get to what a divergent plate boundary is in the next paragraph. Continental plates are made up of mostly granitic type rocks and are mostly felsic, or appear light in color due to their high silica content.
Now that you are familiar with plates, we can discuss how they interact with each other. There are three main plate boundaries called convergent, divergent, and transverse (transform). A convergent plate boundary is when two plates collide. Think of it as a head on collision in a car crash. There are two types of convergent plate boundaries. One type is called subduction, where one plate slides under another which almost always occur off the coast of a continent. The plate that subducts is always an oceanic plate because it's more dense due to basalt being more dense than granite. There are more atoms per square inch in basalt than in granite, making it more dense and more heavy. Heavy objects tend to sink towards the bottom like a penny in a glass of water. Lighter objects will float like an ice cube. Ice cubes can move around in the surface of the water, like how tectonic plates move and interact.
Divergent plate boundary are when two plates move away from each other. These happen almost always in oceanic plates because they are much thiner than continental plates, more easily to tear apart. It's easier to rip a tortilla than a pizza. In the ocean, we call these mid-ocean ridges. They create mountains in the ocean. As lava pours out and hardens, new lava flows on top and so on. It's like a scap. Its height keeps growing. Sometimes it even reaches the surface of the ocean. Iceland is a great example where you can literally stand in the mid-ocean ridge.
Transverse, transform, or strike-strip plate boundaries whose names are synonymous, slide passed each other. The San Andreas Fault is a transform fault. Most transform faults occur in the ocean because it's hard to rip continental crust from side to side due to it's thickness. The San Andreas Fault and it's associated faults is a rare and unique exception. There are two types of transform faults and it depends on how you view it. One is called a left-latteral strike-strip fault and the other a right-lateral strike-strip fault. To know the difference, you can observe the direction of relative movement. If you are on one side of the plate, looking towards the other and the land moves to your left then it's a left-lateral strike-strip fault. Likewise, if the land moves to your right, it's a right-lateral strike-strip fault. Seems easy enough, right?
Now that you are familiar with the different types of faults, we can discus as to why they move and the forces behind it. The answer can be found in your kitchen, literally. When boiling pasta on the stove, the hotter pasta floats to the surface then when it cools it sinks. This effect has a name. Convection currents in your pot at home and in the earth are nearly identical. There are a few difference though. One is with water, rather than boiling rocks and the other is that one is less a few inches while one is miles deep. Convection currents are continues cycles in the earth's mantel that make hotter rock rise, and cooler rock fall and the cycle begins over and over again. When this happens, it causes fractures in the earth's crust. When fractures occur, a fault line is created.
Now at this point I'm sure you are asking, "What is a fault line?" Well it's more of a fault zone since it's a collection of cracks rather than one single crack. Simplicity, it is place where two tectonic plates meet and create friction. When this friction is released, an earthquake is formed. This friction is formed by these convection currents. When they move in a circular pattern in one direction, they can push rock with them. When tension is released you get an earthquake that moves in waves on the X, Y, and Z axises. X is up or down, Y is right or left, and Z is pivoting side to side.
Okay, you're familiarized with different types of plate boundary and faults. Great! Let's discuss how that plays a role into Lover's Peak. About 50 million years ago, the San Andreas Fault didn't exist. The entire west coast of North America was an active subduction zone, creating volcanoes about 100 miles inland which can still be seen today at the Cascade Mountain Range in northern California up to Canada. During this time that Lover's Leep was forming, the volcanoes about 100 miles away would be the modern day Sierra-Nevada since all of them are now considered to be a volcanic plug, just like what you see here but on a much larger scale. The plate that was subducting was called the Farallon Plate. This plate was uneven, meaning eventually it would be two separate plates. Today, this is known as the Juan de Fuca which continues to create volcanoes in the Cascade and the Cocos Plate in Central America.
Over time, the Farallon Plate was "eaten" by the North American plate. In order for the Farallon Plate to move like it did, it needed a divergent plate boundary on the west side to propel it into and under the North American Plate. These divergent plate boundaries would often create undersea volcanoes, similar to what we see in Iceland. But unlike Iceland, they never made it to the surface of the water until recently.
Lover's Leep was created when an undersea volcano, from one of these divergent plate boundaries between the Farallon and Pacific Plates, had an underground tube or channel called a fissure. This fissure would funnel magma to a specific point away from the divergent plate boundary. Lava would pour out of this single vent, instead of a long line of vents, making it a bit more pressurized, leaving to slightly more energetic eruptions. Think of it like a fire house. More pressure, means more power and volume. Eventually, this lava would cool and build up on top of itself This type of volcanism is called a cinder cone volcano. Cinder cones have steep sides, making them prone to erosion hence why not much of the original volcano can be seen today.
Because the lava that comes out of divergent plate boundaries are basaltic in nature, it has a tendency to move vary rapidly and produce less energetic eruptions. It makes it pile up on previous eruptions creating huge volcanoes called shield volcanoes which can be seen on the Big Island of Hawaii. That's why we don't see any many explosive eruptions and it's also why these volcanoes can grow very big very fast. It's why when driving on 152, you can see lots of basaltic ingenious rocks. And although they don't look like flat flows, due to erosion, they do cover a wide area.
Overtime, the when the Farallon plate fully subducted and broke into two, the volcano here ceased a short time after. This lava fissure underneath this volcano cooled much more slowly, allowing larger crystals to form, making it more hard and durable. This means erosion by wind and water would take longer for it to take an effect verses the other types of softer rock formed from a volcano such as tuff and silt hence why there is no evidence of either rock. But because igneous rocks are denser and are more durable, it is left behind for millions of years after the volcano has already went extinct. What is left behind is called a volcanic plug and it does literally show what's inside a volcano.
When the Pacific Plate and North American Plate first made contact, it was underwater in the Pacific Ocean. Rising tensions began to add up and created a new type of plate boundary called a transform boundary somewhere on the eastern side of the Pacific Plate. This is the creation of the San Andreas Fault about 25 million years ago. Note that where this subduction zone was is not necessarily the same exact place where the current San Andreas Fault is today. They are not the same, but they are similar. Due to the friction between these plates, the west coast began to rise literally out of the ocean at a rate of 1 to 2 millimeters per year and they continue to rise today, uplifting the California Coast Ranges which these mountains are a part of including Lover's Leap.
Works Cited
http://www.take25tohollister.com/2011/05/lovers-leap_24.html
http://melanie1167103.edu.glogster.com/volcanoes-cinder-cone-shield-compositestrato-and-lava-domes/
TO LOG A FIND ON THIS CACHE YOU MUST GIVE ME THE CORECT ANSWERS. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
1. "Lover's Leap" on the first line of your email AND list all geocaching names of your party so I can match your answers to them. Note, this IS cheating as only the person who sent their answers has learned something, while the others get a "free ride". It's not fair to others. If you all want to learn something, I would prefer each cacher send me individual emails in the spirt of earthcaching.
2. Estimate the hight of the plug itself, not including the height of the entire mountain.
3. Does the plug have columns like Devils Tower or does it have a more rock-like structure that of Morro Rock AND explain why you see one or the other.
4. Explain the weathering processes here and how they have effect the plug. Don't explain what happened millions of years ago, explain what is currently happening.
5. What evidence is there that this was a cinder cone volcano?