Plate Techtonics!

[Nyril]

Several years ago (more then one, less then ten thousand) the idea that the Earth was not the center of the Universe was high in the ranks of things we argued about. Neatly behind that would be the age of the Universe, age of the Earth, the Earth goes around the sun, Earth is flat, etc. In time, a number of these ideas were accepted by pretty much everyone. By that I mean that I doubt even YEC will argue the point that the Earth is the center of the Universe and in addition to being flat also has the sun and everything else revolve around it.

On that line of thinking, I'd like to ask what you think of plate tectonics in that regard. It isn't brought up much on these boards, but because it neatly explains how we get fossils and strata on opposite sides of the Ocean all neatly lined up (such as the shore between Africa and South America), I imagine there must be some controversy surrounding it.

So, plate tectonics, is it like the Earth being round, or closer to evolution in terms of the amount of public debate surrounding it?

[Jose]

There are many instances in which some topographical feature (fig 1) is filled in with new sediment, with a flat surface on top (fig 3). On a small scale, dinosaur footprints are of this sort, as are worm burrows, trilobite tracks, etc. On a slightly larger scale are "ripple marks" where a shallow sea or lake formed ripples in the sand, then dried up. When new sand was deposited on top of it, the new layer is ripply on the bottom, and smooth on the top--unless it, too, forms ripples. The Moenkopi sandstone in the San Rafael Swell of southern Utah has repeat after repeat of this pattern. I have a couple of nice pieces of ripple-rocks on display among my ammonites and skulls (now there's a nerd--decorates his house with skulls and fossils. weird.)

On an even grander scale is the Grand Canyon, in which we see the strata of the Vishnu Schist rotated, then eroded, and the newer layers deposited horizontally on top of it.


Why are strata folded in parallel?--as in your figure:

The short answer would be that all of the layers were formed by sedimentation, then--quite some time later--they were subjected to compression. Probably, they were deep below the surface during the compression (a geologist looking at the rock samples could probably tell you). Later, they were uplifted, then eroded to produce the mountains with folded strata.

If we were to bury the mountains again, and deposit new sediment on top of them, we should, I would think, see your figure 3--wiggly bottom to the new sediments, but flat, horizontal surface, as in the Grand Canyon. These kinds of junctions between folded or rotated, eroded rock with much younger rock deposited on top, often horizontal when the older strata no longer were, is an "unconformity." The Vishnu Schist and the rock above it is The Great Unconformity. A lot of rock was eroded away before the new layers were deposited.

Probably, the best description I can find now (at least, with the nicest drawings) is here. It describes various sorts of unconformities, which are easier to see in schematics than in real life. Still, here are some examples of unconformities:



... "disconformity", of which an apparently-classic example is in the Grand Canyon. In this image, note the lower line follows the top of the eroded surface, which is filled in by additional horizontal layers above it, just like your figure 3.

Another question, when the mid-Oceanic ridge "pushed" the continents apart, exactly what was the plates that got pushed? How big are they? Where are the boundaries of the plates?

The pushing and crashing terminology is a bit vague, isn't it? As I understand it, the ocean ridges are cracks that continuously spew out stuff. This pushes the ocean floor away from the crack, by establishing new rock next to the crack (which, when pushed up into mountains where we can quarry it, becomes travertine). As the ocean floor spreads outward from the crack, it pushes into the lighter continental plates. The Mid-Atlantic Ridge (one of these cracks) pushes North America away from Eurasia. These continents are moving apart at about 4 cm per year. On the other sides of these continents we have the Pacific, which doesn't have a mid-ocean ridge. So, the continents ease over the Pacific floor, which is "subducted" below it, creating the Ring of Fire. This is the ring of volcanoes from the Andes up through the Sierras and Cascades to Japan and the Phillipines.

I find the Sierras very annoying to look for fossils in, because so much is granite. This comes from the rock that is subducted beneath the continent, melts, and comes back up as granitic intrusion and/or basaltic eruptions. The Sierras are mostly un-erupted granite; Mt. Shasta, Mt. Hood, Mt. St. Helens, and Mt. Ranier are basaltic volcanoes which erupt quite happily.

But back to your question: what are the boundaries of the plates? Because the North American Plate (light-weight rocks) is crawling over the Pacific Plate (heavier rocks), we can define a boundary at the west coast of the US. Almost. The San Andreas fault defines another plate boundary, because the stuff to the west is moving northwest as the Pacific Plate rotates a bit. If I've remembered, I've put a figure below, modified from Campbell's biology textbook. It shows the outlines of the major plates, and their directions of movement. I'll note that the spreading centers of the mid-ocean ridges, and the directions and rates of movement, have been measured, and are clearly fact. The ocean trenches (like the one off the coast of Japan) are the subduction zones. Because the Pacific floor is moving toward Japan, and because Asia is moving toward the Pacific, and because the Pacific floor is going down at that junction, and volcanoes are coming up, it is a logical conclusion that the ocean floor is being melted, and provides the raw material for the volcanoes.

[otseng]

A brief caveat before going on - I'm not an expert in this field and I don't pretend to be.

As am I. Heck, I never even took a course in geology. I too am learning just like all of us.

Suppose a series of strata is at depth, and plate convergence causes uplift - this is a gradual process, remember. Does the resulting deformation affect only the bottom-most strata, or every stratum from the bottom up? Where would the top-most strata go if only the former are deformed?

Yes, uplift would cause the entire series of stratas to deform. This makes sense. But again, why do we see parallel layers practically everywhere in sedimentary rocks? Why do we not see my examples in figures 3 and 6 throughout the rock record?

The fault keeps occurring, even as the process of cementation is taking place in the new rock layer.

It's true that faults move in fits and starts, but they aren't just one-shot phenomena, as anyone living in southern California can bear out.

Yes, but do faults occur again at the exact same spot as the last one? This seems to be what you are suggesting in your explanation.

Again, I don't believe I am asking for too much. All I'm asking for are images like figure 6. One would think that it should be quite easy to find.

The effects of tectonics are all gradual over geologic time-scales, no matter how sudden the individual actions - your figures would work perfectly if plates moved quickly enough for each layer to be neatly deposited and then deformed. But I don't think it works either that quickly or that sequentially.

The burden of proof is on those who believe it took a long time to be accomplished. We cannot simply say, "Oh, it took a long time for it to happen." This response seems to be quite common to my questions, but it does not adequately address the issues. The question still remains, how exactly did it occur over a long period of time?

when the mid-Oceanic ridge "pushed" the continents apart, exactly what was the plates that got pushed? How big are they? Where are the boundaries of the plates?

You write as though this 'pushing' were some sudden action, which may not be the best way to look at it. The Mid-Atlantic Ridge is constantly causing the plates to diverge, and constantly making plate material. As to the latter questions, I don't think they can be answered - plate material melts into the asthenosphere as it is submerged, or accumulates in mountain ranges as plates converge. The boundaries of the plates, therefore, are gradually changing.

Regardless of the time frame involved, the questions have not been answered. (I'm not expecting you necessarily to answer these, but for anyone to answer my questions.)

[Jose]

I'm guano have to run in 5 minutes, but I'll attempt a brief note: Geological time is really hard to imagine. It's like money: we get upset if we get $5 in change instead of $10, but it doesn't phase us much if the national debt is 300 billion or 400 billion. The numbers are just too big to comprehend.

I'm also feeling the edges of an idea, but it hasn't formed well yet. There are two issues here. One is the folding that can occur when rocks are way down underneath lots of other stuff. Another is the cracking and faulting that we see occurring way up here on the surface (as in LA). There is undoubtedly rather different dynamics in the two places. By the time we see faults, the rock is cool and brittle. When the rock is deep, it may be easier for it to "flow" (very slowly). The trick is to develop some kind of "mental movie" of a continent tilted to one side, and getting covered with sediment on that side, then bumping into some other plate and having the deeply-buried layers get compressed, then lifted up, and cracked as the faults break to relieve stresses. I think I can see it vaguely...

[otseng]

Another image for consideration.

Let's take figure 1 again.


Now, instead of layering sediments that completely cover all the folds, let's only cover it with a thin layer. The new layer would naturally go into the lowest parts of the terrain. Then let's repeat. What we would expect to find is figure 7.

Figure 7

Do we have such examples in the rock record? If not, why not?

Let me repeat my argument here against plate tectonics. Plates have been moving for millions of years. These movements are strong enough to form the major mountain ranges. Yet, there is remarkably little evidence of such movement in the rock record. One would expect to see folds and faults throughout all the layers (or even some layers) as in figures 3, 6, and 7. The only time that we see folds and faults are for all the layers. That is, folds are seen from the top most layer on down. Faults are seen from the top most layer on down. This would indicate to me that folds and faults have occured recently. If folds and faults have occurred in the past, why don't we see the figures that I have presented? And as I have argued before, such examples of old folds/faults should at least be on the order of 600 to 1 to modern folds/faults.

[otseng]

Subduction zones (and the volcanoes they produce) are evidence of one plate being pushed beneath another - lithospheric material is melted here and becomes part of the asthenosphere or is forced upward into an eruption.

For subduction zones, my main issue with it is that we are talking about rocks here. How can layers of rock "slide" under another layers of rock? Would not rocks rather be subject to compression rather one sliding underneath the other? What force is causing one plate to move underneath another? Are there factual evidence (measurements) to support the idea that the crust is moving down into a subduction zone?

A primary factor is the relative bouyancy of the continents and plates on top of the aesthenosphere. This is a vast oversimplification, but because the ocean plates are made up of heavier elements -- megnesium, iron -- and the landmasses are made up of lighter elements -- silicon, aluminum -- the continental plates are more bouyant than the ocean plates. This principle is called isostacy. This is why continental plate boundaries are not subducted. You will only find subduction in ocean plate boundaries, and this is due to gravity.

Again, a problem with this idea of buoyancy is that we are talking about solids (and you can't get much more solid than a rock). How can rocks "float" on top of another rock? Whether a rock has a density of 3, 4, or 5 g/cc, it does not mean that one rock can float on top of another rock. If a rock sequence with 3 g/cc collides with rock sequence of 4 g/cc, I would expect them both to compress rather than the "lighter" rock to simply float on top of the "heavier" rock.

Similarly, in thrust faults, normal faults, and reverse faults, one side of the fault is constantly moving either upwards or downwards (albeit in a punctuated fashion), which means that any layers that get set down upon them are also subject to the fault.

I have a hard time accepting that faults will occur continually at the exact same spot for millions of years. But, even if it was true and done in a punctuated fashion, we should still be able to see new layers with no fault lines when another fault activity has not occurred yet.

This model would predict something about layers and faults that a Creationist model wouldn't predict, namely that the distance between layers on a fault would not be the same. That is, over time, the newest layers would have moved less.

Again, I don't want to go too much into the Flood Model here, but I do have a possible explanation for your image. The strata that seems to have the most disparity in height is the strata with the words 'SMALL FAULT' in it. I would suspect this is not as dense as the other stratas. When the fault occurred, the left side experienced more compression. Since the layers were still "wet", it got more compressed than the right side. Thus we see a shorter height for the one on the left than on the right.

[otseng]

The short answer would be that all of the layers were formed by sedimentation, then--quite some time later--they were subjected to compression.

This would make the most sense to me also. The layers would have to have been formed first, then compression occurred. And it appears that practically all folds around the world were created this way. This is strange if plate tectonics is true. Why would compression only occur after all the layers have formed? Shouldn't compression also have occurred while the layers were forming?

... "disconformity", of which an apparently-classic example is in the Grand Canyon. In this image, note the lower line follows the top of the eroded surface, which is filled in by additional horizontal layers above it, just like your figure 3.

I will leave discussion on unconformities and disconformities in the Q's for U's thread. These are more generally explained through erosion, rather than rock movement. So, I think discussions on folds/faults would be more relevant in this thread.

As I understand it, the ocean ridges are cracks that continuously spew out stuff. This pushes the ocean floor away from the crack, by establishing new rock next to the crack (which, when pushed up into mountains where we can quarry it, becomes travertine).

I would agree with the first statement. But that fact does not prove the second statement.

Here is one evidence that the second statement is not true. If we look at the mid-Oceanic ridge, we see that the ridges do not extend all the way to the continents. If the continents were once touching and the ocean ridges were constantly expanding while pushing the continents apart, we should see evidence of the old ridge extending from the edge of the continents. Yet, there is none. Also, we see undersea mountains scattered between the continents and the ridge. How did these form?

[Jose]

Another image for consideration....

Figure 7
Do we have such examples in the rock record? If not, why not?

We do see such examples. Although it's not a great picture, the photo of the Grand Canyon disconformity illustrates this.

Let me repeat my argument here against plate tectonics. Plates have been moving for millions of years. These movements are strong enough to form the major mountain ranges. Yet, there is remarkably little evidence of such movement in the rock record.

Actually, there is lots and lots of evidence. First, however, it might be good to remind us that the plate movements have been observed and measured, so any explanation of the things we see should take these movements into account. Also, there is a record in the ocean floor of the direction of the earth's magnetic field at the time the rocks were deposited--and this record helps understand how the ocean floor has been produced, and how it has moved and continues to move.

Now, suppose we look at the Appalachian Mountains. They're old, well-eroded mountains. They have lots of bent and folded rock layers. These observations indicate that they were created a very long time ago, and that their creation involved lots of stresses. Well, what direction are they moving now? Along with the North American Plate, they are moving away from Europe (or Europe is moving away from them, or both are moving away from the Mid-Atlantic Ridge, where new ocean floor is being formed). So, there was no collision of plates recently that can account for the Appalachians. Now, suppose we work backwards, and say "last year, these continents were 4 cm closer. The year before, they were 4 cm closer still...How many years has it been since they were touching, if they have been moving at this rate?" We get a time somewhere in the vicinity of 50-60 million years ago. Only before that time (probably well before) could the eastern side of North America have been compressed up against Europe enough to produce the kinds of stresses needed to create the mountains. That is, the plate movements explain why these mountains are old, and why the eastern part of the US is relatively immune to earthquakes.

The Rockies, Cascades, and Sierras, on the other hand, are much younger. What plate movements are they subject to? Here, the Pacific plate and the North American Plate are sliding past one another. If we think of the plates as balls on a pool table, we imagine that as the Europe and North American balls move away from each other, and as North America and the Pacific moved toward each other, North America and the Pacific collided, lifiting up the mountains, and have now begun to bounce apart, with the Pacific plate rotating a bit as it does so (hence the San Andreas fault).

The geological evidence is that the western US was assembled from several smaller plates colliding with the North American plate. The rock types show discontinuities from the assembly of this plate and that one (check John McPhee for more accuracy than I can give). That is, the Rockies were on the coast when they were uplifted, and these other portions of North America were added on afterwards. The evidence is in the folds of the rocks, the ages of the rocks, the disontinuities in the types of strata, etc. Unlike the Ozarks or the Interior Low Plateaus of southern Indiana and Kentucky, which are horizontal, unstressed strata resting happily on the middle of the continent, the West is really messy geologically. The East is fairly messy too, but shows mostly just the effects of compression and uplift, while the West shows compression, uplift, and the assembly of several smaller plates.

One would expect to see folds and faults throughout all the layers (or even some layers) as in figures 3, 6, and 7. The only time that we see folds and faults are for all the layers. That is, folds are seen from the top most layer on down. Faults are seen from the top most layer on down. This would indicate to me that folds and faults have occured recently.

I think your conclusion is correct. The faults that we see probably are recent. Many of them are still active, which I take as a modest suggestion that they are recent. I haven't looked for information on fault lines in the Appalachians, but they must be there, although the contours of the portions that have slid with respect to each other are now smoothed by erosion. These ancient faults would be identified by vertical or lateral offsets of particular series of strata, just as we see for more recent faults.

If folds and faults have occurred in the past, why don't we see the figures that I have presented? And as I have argued before, such examples of old folds/faults should at least be on the order of 600 to 1 to modern folds/faults.

I have no idea whether your estimate is appropriate (I don't know what all of the variables are), but in general, you are probably right. We should see lots of these kinds of things. Now, things like figure 7, we do see--but we have to look, and also understand what we're looking at. The disconformity in the Grand Canyon seems not to be known by Flood Geologists, probably in part because it is extremely hard to explain by a Flood Model, but also because we have to know what we are looking at to interpret it. I've looked at that same cliff face many times, but didn't see it for what it is--but it's clearly there.

For faults that are in lower strata but not upper strata, I suspect that the expectation is off somewhat. Sedimentary strata usually form underwater, and probably not in areas of active seismic activity. I suggest this (with no data) because it seems likely that sediment will accumulate where the sea floor is not very steep, whereas the ocean trenches (subduction zones) are both steep and deep. So, there might not be many faults in strata that are being laid down. Rather, the faults would be where plate slippage is occurring--and would be most common in the rocks that are being uplifted (as we see today). Once the rock is uplifted above sea level, it is no longer available for sedimentary deposition, but begins to erode instead.

For subduction zones, my main issue with it is that we are talking about rocks here. How can layers of rock "slide" under another layers of rock? Would not rocks rather be subject to compression rather one sliding underneath the other? What force is causing one plate to move underneath another? Are there factual evidence (measurements) to support the idea that the crust is moving down into a subduction zone?

As I understand it, there are measurements demonstrating that the ocean floor is moving and being subducted beneath the lighter continental plates. Now let's see....we might say that yes, compression seems more likely than "sliding." But picture an ocean trench: the sea floor goes along, then bends downward, and then the bottom of the ocean turns and bends upward, eventually to reach the shore of the continent. These bends are compression and deformation. The ocean floor bends more than the continent because it is much thinner. It may bend down, rather than up, simply from gravity. As the continent inexorably moves toward the trench, it most likely folds the ocean floor back on itself, so that the continent sort of sits on the folded bit. By now, the piece of ocean floor that the continent is on is pretty far beneath the surface, and may actually melt and join the magma pool.

I can picture this more easily than a smooth "sliding." I can also imagine that the movement is not at all smooth, and that strain builds up and builds up, until eventually pieces of the ocean floor crack and the continent jolts a few feet forward. This would produce the kind of subduction zone earthquake that recently occurred off the coast of Sumatra.

Again, a problem with this idea of buoyancy is that we are talking about solids (and you can't get much more solid than a rock). How can rocks "float" on top of another rock? Whether a rock has a density of 3, 4, or 5 g/cc, it does not mean that one rock can float on top of another rock. If a rock sequence with 3 g/cc collides with rock sequence of 4 g/cc, I would expect them both to compress rather than the "lighter" rock to simply float on top of the "heavier" rock.

It is necessary to picture more than just the rocks themselves. They are floating on the earth's mantle, essentially a magma pool. It's liquid (from the heat of compression and radioactive decay). The continents are the light elements forming a "scum" on this liquid gloop. It's a pretty thick liquid, so it doesn't move very fast, and things don't happen on the time scale that they do in, say, a saucepan in which we might be making a consumme--but the principles are similar. So, the densities of different rock strata are not the issue, but the average density of the whole conglomerate of layers, relative to the density of the mantle.

I have a hard time accepting that faults will occur continually at the exact same spot for millions of years. But, even if it was true and done in a punctuated fashion, we should still be able to see new layers with no fault lines when another fault activity has not occurred yet.

Think of the faults occurring in the same places as long as there is some kind of relative earth movement in that region. Again, the San Andreas is a good example. As long as the two plates continue their relative motions, there will be strain in this area. The crack that formed first and expanded is what we call the San Andreas. There are gazillions of other faults radiating out and around it, including the Hayward fault that the UC Berkeley football stadium is on top of, and that has offset one side of the stadium from the other by a few inches.

There are places where new sediment has deposited on top of the San Andreas. But, since most of this is above sea level, there isn't much sediment formation. What is forming above it is soil layers. They don't have fault lines through them. The part of the San Andreas that runs up the peninsula through the edge of San Francisco, along I280, is so non-evident that it has been completely covered with housing developments. So, yes, your expectation is met--but the faults are recent ones, the new sediment forms slowly because it is on land, not under water, and, of course, any time the fault slips, it cracks the new layers above it.

The thing about plate tectonics is not only that the movements have been demonstrated, and are occurring now, but also that these movements explain so much of what we see in geological features. Certainly, the idea was heretical when it was first proposed (under the name "continental drift"), but geologists have been convinced--despite their initial reactions--by the weight of the data. I see no way we can wiggle out of it any more.

[micatala]

Quote:
As I understand it, the ocean ridges are cracks that continuously spew out stuff. This pushes the ocean floor away from the crack, by establishing new rock next to the crack (which, when pushed up into mountains where we can quarry it, becomes travertine).

Otseng said:
I would agree with the first statement. But that fact does not prove the second statement.

Here is one evidence that the second statement is not true. If we look at the mid-Oceanic ridge, we see that the ridges do not extend all the way to the continents. If the continents were once touching and the ocean ridges were constantly expanding while pushing the continents apart, we should see evidence of the old ridge extending from the edge of the continents. Yet, there is none. Also, we see undersea mountains scattered between the continents and the ridge. How did these form?

I haven't done the research that Jose has, and am more thinking out loud than anything, but it seems to me that you could explain the absence of 'ridge' away from the central ridge in a couple of ways.

Is it not possible that a combination of compression, erosion, and sedimentation have destroyed or obscured the 'old ridge material' that is far away from the central ridge? As this material moves away from the rift, it may be subject to undersea currents that would produce some amount of erosion. If the crust is thin, it may be that the weight of the ocean pushes down on this material (which is not being replenished as the material around the rift is), pushing it into the softer mantle below. Sedimentation may help to cover up the older material after it has been compressed somewhat. I am admittedly speculating here. Does anyone know if any of these dynamics are possible? Have they already been refuted elsewhere?

The other mountains Otseng refers to could be the result of volcanism.

Jose said:

For faults that are in lower strata but not upper strata, I suspect that the expectation is off somewhat. Sedimentary strata usually form underwater, and probably not in areas of active seismic activity. I suggest this (with no data) because it seems likely that sediment will accumulate where the sea floor is not very steep, whereas the ocean trenches (subduction zones) are both steep and deep. So, there might not be many faults in strata that are being laid down. Rather, the faults would be where plate slippage is occurring--and would be most common in the rocks that are being uplifted (as we see today). Once the rock is uplifted above sea level, it is no longer available for sedimentary deposition, but begins to erode instead.

This seems reasonably possible. I was wondering how common an occurence sedmentation would be, and that the reason we don't see more of Figure 7 type phenomenon is that it may be rare for these to occur.

Looking at Jose's map of techtonic plates, it seems that the folding process would be happening over a fairly small area of the earth at any one time, especially relative to the areas where sedimentation might be occuring. The question seems to be "how likely is it that sedimentation and folding processes occur 'relatively simultaneously' or at least in fairly close proximity timewise?" It seems reasonable that the answer to this is 'not very likely', in which case the types of cases that Otseng refers to would be rare.

With regards to sedimentation on top of fault lines (why do the faults seem to go through all the layers), I wonder if you might see a third possibility where sedimentation only occurs on the 'low side' of the fault, especially if the change in height across the fault is relatively large.

[MagusYanam]

For subduction zones, my main issue with it is that we are talking about rocks here. How can layers of rock "slide" under another layers of rock? Would not rocks rather be subject to compression rather one sliding underneath the other? What force is causing one plate to move underneath another? Are there factual evidence (measurements) to support the idea that the crust is moving down into a subduction zone?

It all has to do with the thickness of the plates in contact. The density of the material comprising the oceanic plates and the continental plates is similar, but because continental plates displace more of the asthenosphere than the thinner oceanic plates do, the continental plates tend overall to be less dense than the oceanic. Where the densities of the lithospheric material are similar enough, yes, compression does occur. That's what Himalaya is. So what's the force causing one plate to move underneath another? Gravity. A more useful answer might be that it is convection of the asthenosphere driving plate movements and gravity that causes the denser materials to sink in it.

Is there factual evidence for subduction? In a word, yes. Using seismography and the relative densities of the asthenospheric and lithospheric material, geologists and seismologists have been able to actually diagram entire areas where subduction was happening.

This would make the most sense to me also. The layers would have to have been formed first, then compression occurred. And it appears that practically all folds around the world were created this way. This is strange if plate tectonics is true. Why would compression only occur after all the layers have formed? Shouldn't compression also have occurred while the layers were forming?

Yes, but tracking each layer there is a gap in time between when they were formed and when compression occurred. When the sediments were deposited, that layer was under one bar of pressure. After more layers were deposited on it, the compression increased steadily. But keep in mind that this was all happening over a very long stretch of time. These layers weren't rock yet. Even when they became rock, compression would still be increasing.

[otseng]

I've got some more questions about the oceanic ridges.

If magma was coming out of the ridges continuously, then what I would expect is that the magma would come out radially. Like if I boil a pot of water and it overflows, it would come out all around the pot. But if we look at the ridge, the ridge material is only perpendicular to the ridge. There is an easily observable "stair-step" pattern in the ridge. How can magma coming out of the ground produce such distinct lines?

Also, why do we see fracture lines running perpendicular to the ridges? How could they have formed?

Why are the surfaces of the ridges so "bumpy"? If magma came out of the ground, I would expect it to produce a much smoother terrain.