Snow Covered
Walking around the peak
I remember well my first time up with Carpis, We parked below the rim. Immediately one senses the air is different,, clear and crisp. The ground was frozen, crunchy and raised into tiny icy columns.There are no trees just stiff hard grasses and lichens. The more primitive species live in the alpine environment. The only people were the guard, and a family from Toluca. Dad exited his car first and did a slow swivel. Mom and the kids followed, mom in medium heels and a leopard coat, the kids already looking bored. Dad took a deep breath and spoke. "You know we live in Toluca and I have never been up here. I thought we should see it." Off they went Dad in the lead, the kids in tow, and Mom bringing up the rear, complaining,, her ankles wobbly from her heels. Carpis and I and began to walk towards the rim. The edge seemed so close, just up the trail although immediately one senses the lack of oxygen and the pulsing of your lungs erase the concept of closeness and far away. Walking is laborious. I looked like one of those greek sponge divers in Florida, out of my element in a brass helmet with lead boots. When
we reached the rim and I had the first glimpse of the crater below I was mesmerized by its size. A huge plug from the last eruption separated two small ponds, one sapphire and the other emerald. It was breathtaking.
On the rim towards Laguna Del Sol and the "plug" on the left
The information about eruptions has been published in various journals yet I have found conflicting results about the size of the ventings. There have been at least three plinian eruptions recorded, about 12,000 years apart, the most recent 10,500 years ago. I have read that the the most recent spewed anywhere from 10km3 - 14km3 of pumice. Either estimate is a mind blowing figure. The last eruption was smaller and took place 3300 years ago.
An excerpt from Living Under The Shadow:
The Upper Toluca Eruption
The Nevado de Toluca Volcano at 4680 meters above sea level is the fourth tallest peak in Mexico. It is 22 kilometers from the city of Toluca and 80 kilometers from Mexico City. The deposits from Nevado de Toluca have been studied in detail since the 1970's (Bloomfield and Velastro 1974,1977, Bloomfield et al 1977 Cantagrel et al 1981) These authors agree in assigning a late pleistocene age for the volcano, with three large volcanic eruptions recognized: a Vulcanian eruption that ocurred in 28,000 BP ( before present) and two plinian type eruptions that resulted in the emplacement of the lower Toluca pumice at 24,000 BP and the Upper Tolucan Pumice c.10,500 BP.
Stratographic studies of the volcano have found a complex history of volcanic construction and destruction of central dacitic domes and secondary collapses that started before 50,000 BP with the latest eruptive activity occurring at 3300 BP. The volcano is currently dormant but its past history suggests that a plinian eruption scenerio might be possible in the near future. Such an event would put 30,000,000 people at risk in the modern metropolises of Toluca and Mexico City.
The Upper Toluca Pumice was produced by the largest plinian eruption of the Nevado de Toluca volcano. The ashfall to the northeast of the volcano covered a minimum of 2000 km2. This together with the total volume (dense rock equivalent) of erupted magma 14 km3 rank this volcanic event as one of the largest recorded in central Mexico during the late pleistocene era. We know that humans were already present in the basin at the time of this eruption as the oldest radio carbon dated paleoindian so far is the semi complete skeleton of Peñon Woman III with an age of 10,775 BP. She along with two other skeletons found may be the first victims of volcanic action in mesoamerica.
What Xinantecatl has done is change everything around itself. Several years ago we were hand-digging a well and at three meters down we encountered branches of wood. The fellows I was working with, Tomas and Cesar, said when they were digging other wells in the area they found trunks of trees at that same depth. I held the grayish wood in my hand and it began deteriorating in the sun like a movie vampire. Quickly I put it in sealer which stopped the deterioration. I still have the wood. (By the way as a footnote those skeletons mentioned above were found at a depth of three meters). It gave me pause however to think about the origin of that wood,,, so I developed my own geologic history. Tenancingo is a high valley, 2020 or so meters above sea level. Toluca, to the north, 2660 meters above sea level sits upon a large plain. Underneath most of the Toluca area is volcanic pumice from eruptions of Xinantecatl evident in the many gravel pits some of which are 30 or 40 meters deep. I imagine the pumice runs much deeper except usually the water table is encountered and the gravel operation ceases. To the west of Toluca it is marshy where the Rio Lerma begins. Near the river one can still see ponds and vast cattail marshes. My theory is derived from three sources,, the wood found in my well, the marsh near Toluca, and the volcanic pumice. Simple, but then again I am a simpleton. I believe before the plinian eruptions of Xinantecatl which blanketed the Toluca Valley in ash and rock the entire area from Toluca to Tenango was a large deep lake. At some or various points in its eruption history the lake breached its natural retaining wall outside of Tenango and a cascade, or several cascades of mud, rushed towards Tenancingo, more or less following the present path of highway 55. The onslaught of mud from Tenango raised the Tenancingo valley 10 feet just like that, destroying and entombing the trees.It most likely changed the climate to one more temperate.
At this time in its geologic history Tenancingo itself may have been a marshy area or lake. I say this because there are hand dug wells everywhere. Water can be had at from 6-10 meters, enough for a household. When we arrived at 6 meters while digging the well the soil changed to black like old lake bottom or perhaps just an indication of another previous eruption. I suspect an inundation of mud may have occurred several times in Tenancingo. The city's artesian wells average about 150 meters and never encounter bedrock. They do however hit a deep layer of golden sand at about 70-100 meters. I wonder where that came from?
Let me talk about the large black line I mentioned at the beginning of this entry, the one Rodolfo's father exposed while removing the hill. At that time ten years ago I kept bringing it to the attention of everyone I met but no one seemed interested. Very few have the time or luxury for wonder. Soon after my exhortations the evidence was erased as they removed hundreds of truckloads of dirt.I don't know the correlation between meters of soil and time. I wonder how long ago the magic marker line was laid down on the soils of Tenancingo.
Nice photos and story.
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