Robert Titus

An image of the past – the Schoharie Creek Valley

The Catskills Geologists; The Mountain Eagle

Robert and Johanna Titus; Nov. 10, 2017

We love to drive around in the Catskills. There is always so much scenery to see. Even at 55 miles per hour you can look and see so much, at least the passenger half of our marriage can. But sometimes – no frequently – we feel the need to stop and get out so that we can stand along the side of the road and just gaze – into the past. Let’s do that in this week’s column.

Our journey will take us to the Schoharie Valley, midway between Middleburgh and Schoharie itself. There we find a special sort of imagery. Take a look at our photo. We are looking east from Rte. 30. In the distance is a hill with the unlikely name of “Rundy Cup Mountain.” In the middle foreground is the valley floor of Schoharie Creek. It’s pretty, don’t you think? That valley floor is remarkably flat and that is important, but first let’s concern ourselves with Rundy Cup Mountain. We want you to look again and notice something you might have missed the first time.

There are sharp boundaries between agricultural fields and forests on the slopes of Rundy Cup Mountain. And those sharp boundaries define a nice curvature to the lower slopes of the mountain. There is not a trained geologist in the whole world who would not immediately see what we saw. We looked, and then turned around and looked west; we saw the same curvature on that side of the valley. That curvature defines what we call a U-shaped valley.

And that is the dead giveaway to the valley’s long ago history. A U-shaped valley, like this one, is always the product of a valley glacier. We looked again and, in our mind’s eyes, we gazed into the past and saw the Schoharie Creek Valley filled, almost to the top, with a glacier. Our mind’s eyes rose up into the sky and we looked down on it. We had returned to an episode of time, late in the Ice Age. We looked south, and we saw that glacier, confined by the valley walls, and moving like a river of ice, south through the valley. The white surface of the ice was fractured by great, dark, curved crevasses. These curvatures betrayed a southward motion to the ice.

We, the mind’s eyes, paused a full thousand feet above the ice. It was a warm day, by ice age standards. Meltwater, in abundance, had accumulated beneath the ice, and it was lubricating that southward motion. We hung in the air and listened; we heard creaks, and groans emanating from the moving ice below us. From time to time, great, explosive, cracking, echoing sounds followed. On this day the brittle ice was advancing at the unheard of pace of 100 feet per day!

It had been a clear ice age mid-June morning, but now it was late afternoon. The sun shined down directly on the ice and a thick ground fog had formed. The fog rose up and enveloped us; we could no longer see the glacier. When the fog finally cleared, it was very late in the day, but it was a very different day. We, the mind’s eyes, had traveled centuries through time – the mind’s eyes can do that. We had arrived at a time, long after that valley glacier had melted away. Now, the entire bottom of the Schoharie Creek was filled with a sizable meltwater lake. Its waters stretched out as far as we could see to the north and to the south. Beneath those waters, sediments of silt and clay were accumulating.

Now we were able to put together the whole story of this part of the valley. Those curved valley slopes had been sculpted by the passing ice; the flat valley floor was younger; it dated back to the level bottom of that post glacial lake.

Contact the authors at randjtitus@prodigy.com. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.”

Our Reader’s Rocks: the Origins of flint.

The Catskill Geologists; the Mountain Eagle, Oct 17, 2017

Robert and Johanna Titus

Dear Bob and Johanna: My husband and I were out exploring north of Rte. 145 (near intersection of County Rtes. 443 and 156) in Berne when we found an interesting outcrop. One of the rock strata had peculiar black masses within it. I am sending a photo. Can you tell me what this is? Debra Teator, Freehold.

Thank you Mrs. Teator. You did the right thing sending us a photo. They can be very helpful. We can’t always identify geologic features from a photo, but this time we can. The gray rock surrounding those black masses belongs to something called the Helderberg Limestone. We expect to be writing a lot about the Helderberg as it is a very important local unit of rock. Its most important aspect is that it takes us back about 400 million years to a time when almost all of our region lay beneath the waters of a shallow tropical sea. If we could transport you to that Helderberg Sea, you would look around and swear that you were in the Bahamas.

The Helderberg Limestone is very well exposed at John Boyd Thacher Park, and we did not know of your outcrop in Berne. The Helderberg is composed of several subunits called formations, and this one is the Kalkberg Formation. Its sediments were deposited well offshore, in waters that were certainly not deep but might be best described as subtidal. If you were at the bottom of the Kalkberg Sea during the daytime, then you could look up and probably see a lot of sunlight.

Now, what is chert and how did it form? Chert is described as being microcrystalline quartz. That makes one of nature’s most common types of minerals: quartz. But, unlike normal quartz, its crystals are extremely small. That’s the easy part; what is harder is figuring out exactly how it formed. Late at night, in geology bars, this has always been the subject of debate. We will tell you our best understanding.

The first thing that happened is that the sediment that makes limestone was deposited. This stuff consisted of very small grains of calcium carbonate (CaCO₃). Most of those grains had previously been parts of the shells of shellfish. Clams, snails and other shell-bearing organisms had died and their skeletons had broken up into grains of sand, silt and clay.

After this sediment had been deposited but before it hardened into rock, it was affected by chemical processes. If we understand it properly, water rich in dissolved silica (SiO₂), was being squeezed out of the soft, wet sediments. When the dissolved silica reached layers of sediment that had a low pH, which is also known as a high acidity, then the microcrystalline quartz crystalized as chert. The chert formed into globs which are commonly called chert nodules. If the nodules grew large enough and were abundant, then they would grow into each other and form strata of chert. That is what is seen in the photo.

So, today’s journey into the past has taken us into 400 million year old sediments and allowed us to watch the formation of chert. This material is better known to most people as flint. That’s the stuff that Stone Age cultures learned to fashion into stone tools, such as arrowheads. It also functioned in flintlock rifles.

Contact the authors at randjtitus@prodigy.net. Join their facebook page at “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com.”

   Have you found some geology we might want to write about? Send us a photo.

Our reader’s rocks: the origins of flint.

The Catskill Geologists, The Mountain Eagle, Oct 27, 2017

Robert and Johanna Titus

Dear Bob and Johanna: My husband and I were out exploring north of Rte. 145 (near intersection of County Rtes. 443 and 156) in Berne when we found an interesting outcrop. One of the rock strata had peculiar black masses within it. I am sending a photo. Can you tell me what this is? Debra Teator, Freehold.

Thank you Mrs. Teator. You did the right thing sending us a photo. They can be very helpful. We can’t always identify geologic features from a photo, but this time we can. The gray rock surrounding those black masses belongs to something called the Helderberg Limestone. We expect to be writing a lot about the Helderberg as it is a very important local unit of rock. Its most important aspect is that it takes us back about 400 million years to a time when almost all of our region lay beneath the waters of a shallow tropical sea. If we could transport you to that Helderberg Sea, you would look around and swear that you were in the Bahamas.

The Helderberg Limestone is very well exposed at John Boyd Thacher Park, and we did not know of your outcrop in Berne. The Helderberg is composed of several subunits called formations, and this one is the Kalkberg Formation. Its sediments were deposited well offshore, in waters that were certainly not deep but might be best described as subtidal. If you were at the bottom of the Kalkberg Sea during the daytime, then you could look up and probably see a lot of sunlight.

Now, what is chert and how did it form? Chert is described as being microcrystalline quartz. That makes one of nature’s most common types of minerals: quartz. But, unlike normal quartz, its crystals are extremely small. That’s the easy part; what is harder is figuring out exactly how it formed. Late at night, in geology bars, this has always been the subject of debate. We will tell you our best understanding.

The first thing that happened is that the sediment that makes limestone was deposited. This stuff consisted of very small grains of calcium carbonate (CaCO₃). Most of those grains had previously been parts of the shells of shellfish. Clams, snails and other shell-bearing organisms had died and their skeletons had broken up into grains of sand, silt and clay.

After this sediment had been deposited but before it hardened into rock, it was affected by chemical processes. If we understand it properly, water rich in dissolved silica (SiO₂), was being squeezed out of the soft, wet sediments. When the dissolved silica reached layers of sediment that had a low pH, which is also known as a high acidity, then the microcrystalline quartz crystalized as chert. The chert formed into globs which are commonly called chert nodules. If the nodules grew large enough and were abundant, then they would grow into each other and form strata of chert. That is what is seen in the photo.

So, today’s journey into the past has taken us into 400 million year old sediments and allowed us to watch the formation of chert. This material is better known to most people as flint. That’s the stuff that Stone Age cultures learned to fashion into stone tools, such as arrowheads. It also functioned in flintlock rifles.

Contact the authors at randjtitus@prodigy.net. Join their facebook page at “The Catskill Geologist.”

   Have you found some geology we might want to write about? Send us a photo.

An ancient river channel

Robert and Johanna Titus

The Mountain Eagle; The Catskill Geologists; Oct. 20, 2017

Every so often, in our columns, we refer to a sizable ledge of sandstone as being the cross section of a Devonian age stream channel. The Devonian part is easy; all of the bedrock in the Catskills is Devonian in age (419 to 359 million years ago). But what about the stream channel part? How, exactly, is it that we know that?  That’s a fair question and we think we should take a crack at answering it. Let’s do that this week. Recently we were over at North Lake, on the Catskill Front. Our primary interests on that day was the ice age history of the land that lies between North and South Lakes. But, we came across a massive ledge of light colored sandstone and it caught our eyes. We took a good look and a good photo. We had seen some interesting structures within that sandstone.

Well, what we had seen were a number of erosion surfaces. We printed up our picture and then inked in those erosions. Take a look at our photo. This had been a sizable river. Its sandstones must be twelve feet or so in thickness. You need a river pretty much that deep just to accumulate all that sand. This river lay at the bottom of the steep slopes of a mountain range. These were called the Acadian Mountains and they towered above what is now western New England. Streams, that descended their slopes, would have flowed out onto what we call the Catskill Delta. They carried a lot of sediment, most of it sand. These sands came to be deposited where North Lake is today. These were likely large and powerful streams. They would have been occasionally subject to great flooding events. It is only logical to think that, from time to time, it rained a lot up in the Acadians. Those storms generated powerful flows of water, carrying large amounts of sand. When the streams flowed far enough out onto the delta then their flows slowed down and the sand came to be deposited.

If all that is true, then we should see the evidence in outcroppings, such as the one in our photo. We think that the evidence is there – in the inked lines. Each flood event must have reached a peak, when the flows were at their maximum levels. Those flows, it only seems logical, would have eroded into the sediments of the stream channel. When we inked in those erosional surfaces, we thought we had identified such events. The bottoms of these surfaces are concave and they, each one of them, look like features that had been eroded.

There are at least four of these erosional surfaces in our outcrop, or about one every three feet. We think that each of these surfaces records the peak of a major flood event. During that peak, the flood currents would have picked up large amounts of sand and swept it away. As the flood passed its peak, currents slowed down and most of that sand would have come to rest as a new deposit. Most of the sand in between these erosion surfaces seems to have been deposited at the end of its flood or during quiet times that followed.

How often did these floods occur? We can come up with a very approximate estimate. There are about 4,000 feet of sedimentary rock found in this Devonian sequence and it took about 11 million years to deposit them. That averages out to about 2,700 years per foot of sedimentary rock. If there were three feet per flood and if all the above is true, that means that these floods occurred every 75,000 years or so! That’s a lot of time. That’s also a guess.

But, most importantly, all this is consistent with the notion that such sandstone ledges were once stream channels.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com”

Integrating Geology into the Local Community

Robert and Johanna Titus

  We are ‘the Catskill Geologists.” After successful careers as academic scientists, we have become popular science writers. We have blended geology into the regional culture of the Catskills and upper Hudson Valley. This started in 1991 when Robert began writing for Kaatskill Life magazine. Later Johanna joined him, and we did four columns per year for 30 years. We published four books as well. These all described the area’s bedrock and Ice Age history, written at a level both readable and, more importantly, interesting to the everyday resident. This led to more than a thousand columns in several of the area’s newspapers, especially The Woodstock Times and today, The Mountain Eagle.

With a growing and widespread popular interest in our region’s geology, came a spillover to work with local civic groups who were looking for lecturers and nature walk leaders. These include the Woodstock and Columbia Land Conservancies, the Mountain Top and Greene County Historical Societies, The Catskill Arboretum and the Roosevelt Presidential Library. Self-guided geology trails were designed for several of those groups.

With sufficient public awareness, a facebook page and a blog site became helpful providing direct communication with readers. There were frequent guest appearances on local radio and television stations. We even hosted our own radio talk show on the local PBS channel WIOX. That focused on the geological history of the Schoharie Creek Valley. Recently we have related the Hudson River School of Art to the local Ice Age history. We argue that the glaciers sculpted the landscapes that inspired the painting.

The theme that we are advocating is that every community has its own local newspapers and magazines. public broadcasting stations, libraries, museums, preserves and other civic groups. All may be open to making a place for well explained geoscience. Our science can be an integral part of our communities and we geologists can enjoy rewarding lives of community engagement.

A Journey through time in Kaaterskill Clove

The Catskill Geologists – The Mountain Eagle; 11-3-17

Robert and Johanna Titus

Have you ever hiked the north rim trail at Kaaterskill Clove? It’s one of those many great experiences that anyone living in the Catskills should have done – perhaps, like us, many times. Better still, it’s something you should take visitors to see. When we go there, we stop at Inspiration Point and look down about a thousand feet or so, and gaze into the distant past. Way down there, about 15,000 years ago, was a raging, foaming, pounding, thundering, whitewater torrent. Those were the waters of the melting glaciers of those late ice age times. That flow did most of the work of carving Kaaterskill Clove. That’s what makes this truly a geological wonder.

But there is still an older time, represented down there. Down in the very depths of the canyon, there are stratified sandstones and shales. The canyon is about a thousand feet deep here, so there must be an equal amount of stratified rock. Those rocks are middle and late Devonian age, which makes them about 385 to 375 million years old – that’s in very round numbers. It’s natural for geologists to ponder such vast numbers. We are pros; we are professional scientists, and we are not supposed to wax poetic about such things, but – we can’t help it.

The two of us began to wonder just how many years had passed by from when the oldest strata, at the bottom of the Clove were deposited, to when those at the top came to be. We got out some publications from the New York State Museum and began to make some “guesstimates.” We are only going to make some gross approximations today; so don’t hold us to any of our numbers. We just want to give you a notion of when all the stratigraphy at Kaaterskill Clove came into being, and how long it took to be deposited. If somebody thinks they can come up with better numbers, we welcome them.

We think the strata at the bottom of the canyon belong to a unit of rock called the Plattekill Formation. The Plattekill is a unit of gray and brown sandstone. The New York State Museum places the middle Plattekill at about 385 million years in age. We think the top of Kaaterskill Clove corresponds with the top of the Oneonta Formation, a largely red sandstone, and that makes it about 381 million years in age. The math is pretty easy; we get about 4 million years of time represented from the bottom to the top of the clove’s stratigraphy. Remember those 1,000 feet that the canyon encompasses? Well, we divide through and we get about 4,000 years per foot of stratified rock.

Now, none of this is great science, and none of it is great math. A foot of river sandstone might have been deposited in a few hours. A foot of red shale may have taken many, many thousands of years to form. There must have been sediments from vast expanses of time that were eroded away and lost forever. Other great lengths of time just never saw any deposition at all. But, we think we have come up with some reasonable approximations and that is all we are aiming at.

Again, stand atop Inspiration Point and look down those thousand feet. See 4,000 years of time for every foot below you.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The

Our reader’s rocks – Ice in Grand Gorge Gap?

The Catskill Geologists; Robert and Johanna Titus

The Mountain Eagle; Sept.15, 2017

We always give our email address at the bottom of each of our articles. And we can always be approached on our facebook page, so we hear from a lot of our readers. Often they have questions and we are usually able to help tem with answers. Every once in a while, we thought we would answer one of these queries in the form of a column so here goes the first.

Recently we heard from a Gerry Hubbard. He sent us a photo of Grand Gorge Gap and wanted to know what the rounded hump on the right is. Take a look at our photo and you can see that hump. We had been wondering the same thing for years and so Gerry’s request got us to do something about the problem.

The first step is to get our topographic maps out and look at them. We found that the Roxbury 7 1/2 minute quadrangle map displayed the Gap. We found that the hump has a name; it is Jump Hill. Then we went back to our photo. The “hump” is actually something that lies in between two valleys. The contour lines on our map indicated a steep but steady slope for each of the two valleys. Each one of those is what geologists call a U-shaped valley. Every trained geologist on the planet Earth quickly recognizes the ice age history of such a valley. They record the passage of glaciers. As ice squeezed through a valley it ground away and eroded the bedrock. The shape that offers the least resistance is the U. Not surprisingly, over a period of time, glaciers will carve those U’s into the bedrock landscape. It gives each of them a path of least resistance. That forms a remarkably picturesque image and that helps make glaciated landscapes so attractive. We geologist are most fond of these U-shaped valleys.

Well, we studied the map and our photo and started speculating about what had happened here, way back, near the end of the Ice Age. Speculation is a word that scientists like to avoid; it sounds so – well speculative. So we use the word hypothesize instead. It sounds better. We hypothesized the following story: We hypothesize that the larger U-shape, on the left, is the older of the two. We think that a sizable glacier entered Grand Gorge Gap and began eroding the large U-shaped valley. Somewhere along the line, the ice was diverted and a second stream of it passed through what is the smaller, and we think younger, U-shaped on the right. All this erosion left Jump Hill in between.

We hope that Gerry likes our hypothesis. It conjures up quite an image. We travel north on Rte. 30 to where we can park and see this view. In our mind’s eyes we can imagine the advance of these glaciers; we can watch them carve the shapes of Grand Gorge Gap. That view gives us a whole new perspective on this site.

We hope you enjoyed our hypothesis. Perhaps you have a location that we could write about. Let us know.

Contact the authors at randjtitus@prodigy.net. Visit their facebook page at “The Catskill Geologist.”

Why Gilboa? By Robert and Johanna Titus

The Catskill Geologists in The Mountain Eagle

Sept. 15, 2017

   Gilboa was, a century ago, a sizable town in the center of the Catskills. We have been told it was once as big as Cobleskill. But fate struck; New York City reached out and took the land the town was built on, and used that for a reservoir. A dam was constructed just a little west of the old town. The village was razed and, when the dam was filled with water, it disappeared altogether. What little is left, is at the bottom of the reservoir

It was a sad fate, and one which is still deeply resented. But, why did it happen? What was it about Gilboa that led to its demise? We decided to see if we could answer that question. We could not go back through time and travel to the offices where New York City engineers were making their decisions. We could not talk to them, or read their minds. And, much of the geological evidence is now hidden from sight, at the bottom of the reservoir. But, there are other sources of evidence. Perhaps we could read those minds!

We have one of the maps that those long ago engineers must have used. It’s what’s called a 15 minute quadrangle map of the Gilboa area, published by the New York State Department of Public Works. Ours is the 1903 edition, so it is the very one that those engineers were likely eye-balling as they searched for likely locations for New York City reservoirs. We could look at this map and think as they must have.

We have selected that part of the map that shows the Schoharie Creek Valley where it stretches from Prattsville, north to the onetime site of Gilboa. That’s where the reservoir went. Take a good careful look. Do you see all those narrow lines? Those are contour lines. They define different elevations. The bottom of the valley was at about 1,050 feet in elevation. If you look carefully, you can see the 1,050 foot contour line, just to the right (east) of the creek.
The bottom of the creek was valley floor flatland. It must have been good farming. Notice the absence of contour lines down there. Flat land has very few, or no contours. But the valley walls are different; there contour lines are closely spaced. A person who, back then, climbed up those slopes would have frequently crossed contours.

Experienced geologists can “read” such maps and learn so much from them. Well, we studied the map and began to see the Gilboa area as it had been, before the reservoir and its dam. We saw that most of the valley floor, all the way south to Prattsville, had been wide and flat. We know that this had been the bottom of something called Glacial Lake Schoharie, and those flatlands must have been lake-bottom silts. Easy to plow, these acres must have been wonderful farmland.

But look where Gilboa was; there the contour lines crowd the valley floor. That’s where the Schoharie Valley had been surprisingly narrow. Those long ago engineers must have seen the potential. Gilboa was located right where the valley was narrow and easily dammed. Behind that planned dam, was a wide valley with a flat floor.

The Gilboa site was ideal for damming; the lands behind that dam would be perfect for a reservoir. Gilboa’s fate was sealed; the town was doomed!

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.”

A visit to Glacial Lake Windham

The Catskill Geologists

Robert and Johanna Titus

The Mountain Eagle – Sept. 8, 2017

Last week we visited Windham, actually the Windham Path, just east of town. We wanted to show you something about the ice age origins of the town. Most of the Windham Path lies upon the floor of what’s called a glacial lake. That lake had come into being when a glacier deposited heaps of sediment in something called a moraine. The moraine can be seen just east of the Path. Most of the land from east Windham to here is rolling elevated moraine landscape. That’s the land lying just east of Mitchell Hollow Road.

Let’s learn some more this week. We would like you to drive west from Windham on Rte. 23. You may have done this before, perhaps many times. But, as always, we want you to be paying more attention to the landscape that you are passing. We, especially, want you to take heed of the flat landscapes down at the bottom of the valley. It would be easy to dismiss this as a floodplain, after all valley floors are supposed to display floodplains. But, you would be wrong; this flat landscape is the floor of an ice age lake. Lake deposits are almost always spread out as flat sheets. That’s what we see here.

These lake bottom landscapes continue at least as far west as Ashland. They speak to us of a glacial lake. It was a big one, extending at least five miles from the Windham moraine to a bit west of Ashland. Rte. 23 lies on a platform that runs parallel to the old lake. That platform also has an ice age origin. It is composed of sediments that were dropped down the northern valley wall and deposited as a lakeshore deposit called a glacial terrace. That terrace was irresistible to highway engineers when they were making Rte. 23. It lifted the highway up onto a well-drained surface.

The top of the terraces was deposited at just about the old lake level. Our topographic map tells us that that level was at about 1,500 feet in elevation. The map also tells us that the lake bottom lay at about 1,450 feet. We can thus calculate that the lake was about 50 feet deep. It got a good bit deeper toward Ashland. Turn south (left) at Jewett Heights Road and, when you get down to the river, stop and get out. You are now standing on the floor of a deep lake! Have you ever done that before?

You might do a little exploring. Look for a vantage point, somewhere above the 1,500 foot level. Now you can look down and, in your mind’s eye, you can survey Glacial Lake Windham as it once was. We picked a day, very late in the Ice Age. The climate had been warming up considerably and the ice had melted off most of the lake’s surface. There was, however, still a narrow shelf of gray ice all around the lake’s shore.

We were hoping to see some animals. Perhaps a mastodon or two might have been walking the shores of the lake. But, we were disappointed. It was not that late in the Ice Age, it was still too cold in Windham.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.”

The Earthquake at Mexico City

The Catskill Geologists; The Mountain Eagle; Sept 19, 2017

Robert and Johanna Titus

For the second time in a thirty years, Mexico City has experienced an awful earthquake. It was actually about 75 miles southeast of the city; that’s close enough. This one measured about a 7.1 on the famous Richter scale. That’s a powerful earthquake. Early reports claim that 40 buildings came down and several hundred people died. We don’t have many earthquakes in our region, and when they do occur they don’t amount to much. Still, we can’t help saying something about it; it has been a big geological event.

Why was it so bad? Well, as we understand it, Mexico City lies within a series of very sizable geological faults. And they are circular faults; the crust has broken up into a series of concentric circles. These are also active faults; they generate earthquakes from time to time. That’s bad enough, but it gets worse. The basin that lies inside these faults has filled with lake sediments. These tend to be wet, and that makes them very unstable during any earthquakes. The seismic waves pass through the sediments and they become liquefied. Mexico City finds itself shaking on a liquefied landscape.
That accounts for a lot of the damage.

We have found a way to demonstrate this. We like to get a thick pint glass out and fill it to the very top with water (beer when Robert is pouring). When the fluid is at the absolute top, we are ready to go on with our “experiment.” We pound a fist right next to the glass and watch the water at the surface. Most of the time we see waves radiating inward from the outer edge of the glass. Something very much like that happens to the Mexico City basin. Perform this experiment in your own home and then imagine the results scaled up to the size of a great city. Now, you understand what happened the past week.

The news is not all bad. These awful events present architects and engineers with wonderful opportunities to learn how to design earthquake resistant buildings.
That’s what happened in 1985, after the last big earthquake in the city. In the months and years that followed, experts studied the buildings that had come down along with those that survived. What, they asked, were the differences? How could new buildings be constructed so as to minimize the threats.

We will give you one example. Mexico City architects found that L-shaped buildings were very likely to collapse during a quake. One side of the L vibrated in one direction; the other half vibrated differently. The competing stresses brought those buildings down. They looked good but they were dangerous. Well, when these buildings were replaced, architects knew better than to use L-shapes.

The long and the short of it is that the rebuilding of Mexico City benefitted from the 1985 experience. Now all those earthquake resistant building have been tested by a new quake. We expect that at this very minute engineers are toting up the scores. Which buildings “won” and which buildings “lost.” Which of the new designs had succeeded and which didn’t?

This is progress, but it is a very expensive way to learn.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The
Catskill Geologist.” Read their blog at “thecatskillgeologist.com.”