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Jim Reynolds |
| I first visited Guatemala my Junior year at Dartmouth as a component
of my Field Camp, in December 1973. On that trip, we visited the country's
active volcanoes. Many of the photos on these Central America pages were
taken then. Oddly, the most significant event of that trip turned out to
be meeting up with two Dartmouth Seniors, John Cleary and Bill Hallager.
They were living on a ranch in south-central Guatemala and mapping Tertiary
volcanic rocks that had never been investigated in much detail. I learned
that this was a long-term Dartmouth project and that Dartmouth undergraduate
Geology majors had been doing these projects for several years. I was immediately
intrigued.
In the fall of my Senior year, I was working at a gold mine for Noranda Exploration in the Platoro Caldera of the San Juan Mountains, Colorado. Knowing that my internship would end as soon as the snow began to fly, I wrote to the late Dr. Dick Stoiber, at Dartmouth, and expressed my desire to do a Senior Thesis in Guatemala. He wrote back immediately, welcoming me to the project. He also said that two of my classmates, Jesse (Jake) Dann and David Hyde would be going as well as a Master's student, Carl Nelson. Carl and I met in Hanover and tried, unsuccessfully to fly out on our scheduled departure date in early January 1975 but were prevented by a heavy snow. The next day was better so we took off for our big adventure--10 weeks in Guatemala. We were met in Guatemala City by Dr. Sam Bonis, an American expatriot geologist who had been living in Guatemala for many years and working for the Instituto Geográfico Nacional (IGN), the Guatemalan equivalent of a geological survey. Sam was also an Adjunct Professor at Dartmouth. We would be working on an IGN internship, each receiving an $8/day per diem along with an IGN vehicle and driver. Jake and Dave had arrived on schedule the day before and were in the field near Escuintla with a group from LSU (Sam's Ph.D. alma mater). Carl and I were driven to Escuintla by Daniel González, who would be one of our drivers in the field. We picked up Jake and Dave and then went back to Guatemala City. The next morning, Sam joined us at our hotel, the Pensión Asturias, and the five of us were driven to the town of Nueva Santa Rosa, the first town out of which we would be working. My first memory of driving into that dusty town, many kilometers off of the nearest paved road, was seeing a boy walking his puppy on a leash. The reason this sticks in my memory is because the puppy was dead and the kid was dragging the corpse through the dust. I realized that there were many things I would have to get used to here. Sam took us into the field and we hiked to the top of a low ridge in the middle of our area. As we ate our lunch, we looked across the broad fertile basin in which the town was situated. On the far side stood Jumaytepeque volcano, a dormant cone. Having just come from working in a large caldera in Colorado, I made the rash statement that I thought the area was a caldera. Sam has a tendency to explode in a comic fury. I was immediately the victim of one of these outbursts and I cowered under the withering stream of profanity mixed with sarcastic humor about how an undergraduate was imagining things in his first hour in the field that seasoned professionals had never seen. Our biggest challenge was the language; none of us spoke any Spanish. Carl and I had had a lot of French and we both rapidly discovered that learning a third language was a lot easier than learning a second. We dove into it and within a week were able to make our basic needs understood. We stayed in Nueva Santa Rosa for three weeks and finished mapping the Nueva Santa Rosa quadrangle which had been nearly completed by two previous Dartmouth groups. Our work was in the northeastern corner of the map. We then moved to the small nearby city of Cuilapa where we began mapping the southeastern corner. Two of our classmates, Dave Beaty and Bill Beyer, had mapped the northeastern corner of the Cuilapa quad in the fall. There are lots of stories to tell about those 10 weeks. Maybe someday I'll write them all down. In the end, Jake and I wrote a credible senior thesis about our work in the Cuilapa quadrangle and Dave wrote about the Nueva Santa Rosa work. Jake and I concluded that the southeastern corner of the Cuilapa quad was a Pliocene-aged volcano which we named Ixhuatán after the town of Santa María Ixhuatán that is situated near its summit. Carl married Sam's secretary, Carmen, and is still living happily ever after as a consultant in Boulder, Colorado. I had been accepted into the Master's program at the University of Oregon but Dick Stoiber talked me into staying at Dartmouth and returning to Guatemala to do a Master's thesis based around the South-Central Guatemala mapping project. I acquiesced and the following fall found myself still at Dartmouth. I returned to Central America in the Fall of 1976 and spent 13 weeks roaming around the Tertiary Volcanic Belt of Guatemala, El Salvador, and Honduras. The first part of the project was to try to take the 9 different Dartmouth mapping projects and build a coherent story out of them. Then I would travel around the volcanic belt and see how our area compared to others in the region. My visit began 4 months after the great 1976 earthquake which devastated the country. The Caribbean Plate shifted eastward about 1 m and > 10,000 people perished. I've included a few photos of the destruction. I wrote a decent thesis and published a paper in Bulletín Volcanologique. I'll admit that I never really felt that I had cracked the case when it came to understanding the south-central Guatemala area. It wasn't until I was a Ph.D. student in 1984, back at Dartmouth again after six years, two jobs, and one stroke, that it became clear. I was standing in the mailroom when fellow grad student Chuck Connor showed me a picture of an intracaldera welded tuff from one of the San Juan calderas in Colorado. It was a finely laminated rhyolite made up of almost pure glass with tiny sanidine crystals in it. I recalled seeing a similar rock along the boundary of the Nueva Santa Rosa and San José Pinula quadrangles near the hamlet of Sanyuyo. If that was an intracaldera welded tuff, then it must be in a caldera!!! Perhaps I was right afterall on that first day with Sam! Once I started using the caldera model, the meaning of the geology of the whole region became clear. Prior to this understanding , I had been agonizing over a manuscript describing the geology of the San José Pinula, Nueva Santa Rosa, and Cuilapa quadrangles. Suddenly, I was able to sit down and write it in about two days. It was published in the Journal of Volcanology and Geothermal Research. Sam Bonis was one of the reviewers; he agreed with my conclusions. Below are some photos of some of the geological highlights of south-central Guatemala. The published work on the area can be found in: Reynolds, J. H., 1987, Timing and sources
of Neogene and Quaternary volcanism in south-central
Two quadrangle maps were also published to accompany the previously published San José Pinula quadrangle: Reynolds, J. H. and others, 1980, Mapa
geológico del cuadrangulo Nueva Santa Rosa (1:50,000). Instituto
Reynolds, J. H. and others, 1980, Mapa
geológico del cuadrangulo Cuilapa (1:50,000). Instituto Geográfico
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| Jumaytepeque volcano straddles the southeastern rim of the Santa Rosa de Lima caldera. This photo was taken from the southern edge of the resurgent dome and looks southeastward across the caldera floor with the town of Nueva Santa Rosa in the center. The caldera was a lake until it was filled with pumice from the Ayarza eruption about 20,000 years ago. I took this photo from our lunch stop on our first day in the field. It was from here that I said that I thought the area was a caldera. |  |
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This image shows most of the southern two thirds of the Dartmouth map area in south-central Guatemala. The mountains on the left are the extinct Ixhuatán volcano. Those on the right are Tecuamburro volcano. With just a little imagination, the Pacific Ocean can be seen between the two volcanoes stretching to the horizon. The Santa Rosa de Lima caldera lies between the point where I was standing and the low range of hills in the center. |
| La Laguna del Hoyo is a large maar situated in the south-central part of the Nueva Santa Rosa quadrangle. Maars are caused by phreatic (steam) eruptions. Hot subterranean magma superheats the ground water to the point where the built-up pressure overcomes the strength of the overlying rock and causes the explosion. This is strictly a steam and debris eruption, however, no new magma is erupted. |  |
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This image shows much of the southeastern portion of the Cuilapa quadrangle where I did my Senior thesis. The hill on the left is probably some sort of andesitic dome. We never really did figure that one out. The area back in the clouds is the collapsed Ixhuatán volcano. The Río Los Esclavos canyon lies just in front of the low hill in the center. It is about 100 m deep and is incised through Pleistocene-Holocene basalt flows and Pliocene andesites. The canyon is there because a splay of the right-lateral Jalpatagua Fault cuts the volcanic strata. |
| The Pliocene andesite cliffs along the Río Los Esclavos occasionally presented a challenge which I was happy to address when I was 22. The real problem with the river was that the hydroelectric project just upstream from here would suddenly begin releasing water and change the river level. More than once we crossed a low stream in the morning and found a strong moving current in chest-high water when we returned in the afternoon. |  |
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Nearly 50 Pleistocene-Holocene cinder cones comprise the Barbarena-Cuilapa cinder cone field. The field apparently originated due to tensional faulting where the Jalpatagua Fault bends around the southern margin of the Santa Rosa de Lima caldera. The cones tend to align along the faults. A few of the cones south of Cuilapa are seen in the middle distance. |
| A Pleistocene basalt flow, from one of the nearby cinder cones in the Cuilapa area, filled an old valley and formed columnar joints as it cooled. The flow was subsequently faulted and cut through by the Río Los Esclavos, seen at the canyon bottom. |  |
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The Río los Esclavos drains the eastern
portion of the south-central Guatemala area. Deciphering the superposition
of the interfingering strata exposed along its banks, with the help of
a few key isotopic ages, were critical to unraveling the geologic history
of the area.
In this photo, the river has cut through a thick bed of pumicious rhyolite that was erupted from Tecuamburro volcano between 20,000-30,000 years ago. Tecuamburro is on the southern boundary of the Cuilapa quadrangle. The flow completely filled in the prexisting canyon and formed a small lake that stretched upstream until the river reestablished its path through the easily-eroded pumice. You can see Carl (red hat) in the lower right, for scale. The white dot at the lower right base of the cliff, above Carl's head, is a local fisherman. The base of the pumice rests on top of Pliocene andesitic lavas from Ixhuatán volcano. |
| Numerous hot springs are present along the Río
Los Esclavos where it cuts between Ixhuatán and Tecuamburro volcanoes.
We measured temperatures over 90º C, suggesting that boiling water,
suitable for geothermal energy, was not far below.
An odd thing about this site is that there is a local cemetery just out of the picture on the left. We wondered how long the deceased had to cook before they were allowed in to heaven. |
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The rugged jumble of steep hills around the town
of Santa María Ixhuatán, as seen from the coastal plain to
the south. After mapping in the area for six weeks, we concluded that the
hills were actually a collapsed Pliocene andesitic shield volcano that
had had a late phase of dacitic dome activity.
In honor of the town near its summit, we named the volcano Ixhuatán. A lot of people live in those hills. We met them on a daily basis as we hiked the numerous trails that criss-cross the area. |
| The figure-8 shape of Laguna de Ayarza was caused by a catastropic eruption that took place about 20,000 years ago, destroying a twinned volcano. Pumice from the eruption blanketed the entire region. The mountain in the background is the northern rim of the Santa Rosa de Lima caldera in the Dartmouth map area. Lake Ayarza is situated in the quadrangle to the east of the Nueva Santa Rosa quad. Since this photo was taken, in 1976, a large hydroelectric project has greatly modified the appearance of this area. |  |
| This bridge on the Atlantic Highway crossed the Agua Caliente River right along the fault line of the 1976 earthquake. The entire bridge tumbled into the water but the supports were left intact. The army had placed a one-lane pontoon bridge across the river. The traffic delays were LONG! This is the only major road between the the Atlantic and Pacific coasts of the country. |  |
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The church at Comalapa was shattered during the quake but somehow managed to remain standing. It was too dangerous to enter and was scheduled to be demolished. |
| The fault line crossed the highway to Zacapa, offsetting the centerline. Tectonically, I was standing on the Caribbean Plate, looking across the Motagua Fault at the North American Plate. As can be seen in the photo, the Motagua Fault is a left-lateral strike-slip fault. The mountains in the background were elevated along other splays of the fault during prehistoric earthquakes. |  |
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Last updated
May 7, 2007