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75-466: The name Florissant comes from the French word for flowering. In the late 19th century tourist and excavators came to this location to observe the wildlife and collect samples for collections and study. The Petrified Forest, which is one of the main attractions at the monument today, lost much of its mass due to collectors removing large amounts of petrified wood from the site. During the 1860s and 1870s

150-410: A slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano , typically along a river valley . Lahars are often extremely destructive and deadly; they can flow tens of metres per second, they have been known to be up to 140 metres (460 ft) deep, and large flows tend to destroy any structures in their path. Notable lahars include those at Mount Pinatubo in

225-413: A distinct dry season. This is much wetter than the average 38 cm that falls in the area during modern times. Most of the precipitation would have come in the late spring to early summer, with the rare snowfall in the winter. Tree-ring analysis indicates that the environment that the redwoods grew in during the time of sediment deposition would have been even more favorable than the current climate that

300-408: A pair of thick horns on the top of its head. All of this information is based on fragmented vertebrae and small pieces of tooth enamel. The oreodont, is an extinct family that resembles modern sheep and pigs. The only oreodont specimen is a jaw fragment. Other mammals have been described in the formation based on teeth specimens. In all, around a dozen mammalian taxa have been discovered and described in

375-766: A potential path of more than 300 kilometres (190 mi). Lahars from the 1985 Nevado del Ruiz eruption in Colombia caused the Armero tragedy , burying the city of Armero under 5 metres (16 ft) of mud and debris and killing an estimated 23,000 people. A lahar caused New Zealand's Tangiwai disaster , where 151 people died after a Christmas Eve express train fell into the Whangaehu River in 1953. Lahars have caused 17% of volcano-related deaths between 1783 and 1997. Lahars have several possible causes: In particular, although lahars are typically associated with

450-411: A small opossum being discovered so far. In the lower mudstone units, there are samples of broken bones of a horse, a brontothere , and an oreodont . The horse would have been small, about as large as a medium-sized dog, with three toes on each foot. All this information is based on a complete lower jaw. The largest mammal that has been discovered so far is a brontothere , an elephant-sized animal with

525-476: A source of silica, but tetraethyl orthosilicate has proven more promising. Petrified wood has limited use in jewelry, but is mostly used for decorative pieces such as book ends, table tops, clock faces, or other ornamental objects. A number of Ancestral Puebloan structures near Petrified Forest National Park were constructed of petrified wood, including the Agate House Pueblo. Petrified wood

600-557: A wall of mud 140 metres (460 ft) deep in the White River canyon and covered an area of over 330 square kilometres (130 sq mi), for a total volume of 2.3 cubic kilometres ( 1 ⁄ 2  cu mi). A debris-flow lahar can erase virtually any structure in its path, while a hyperconcentrated-flow lahar is capable of carving its own pathway, destroying buildings by undermining their foundations. A hyperconcentrated-flow lahar can leave even frail huts standing, while at

675-487: Is a particularly fine example of fluvial accumulations of driftwood. Volcanic ash is particularly suitable for preservation of wood, because large quantities of silica are released as the ash weathers. The presence of petrified wood in a sedimentary bed is often an indication of the presence of weathered volcanic ash. Petrified wood can also form in arkosic sediments, rich in feldspar and other minerals that release silica as they break down. The warm supermonsoon climates of

750-676: Is also used in New Age healing . Petrified wood is found worldwide in sedimentary beds ranging in age from the Devonian (about 390 million years ago), when woody plants first appeared on dry land, to nearly the present. Petrified "forests" tend to be either entire ecosystems buried by volcanic eruptions, in which trunks often remain in their growth positions, or accumulations of drift wood in fluvial environments. Amethyst Ridge at Yellowstone National Park shows 27 successive forest ecosystems buried by eruptions, while Petrified Forest National Park

825-503: Is hydrophobic (water-repelling) and much slower to decay. The rate of decay is affected by temperature and moisture content, but exclusion of oxygen is the most important factor preserving wood tissue: Organisms that decompose lignin must have oxygen for their life processes. As a result, fossil wood older than Eocene (about 56 million years old or older) has lost almost all its holocellulose, and only lignin remains. In addition to microbial decomposition, wood buried in an alkaline environment

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900-413: Is one of the main tourist attractions at the monument with an estimated 30 preserved stumps. They are among the largest petrified stumps in the world. The majority of the stumps have been identified as belonging to Sequoia affinis , a close relative of the modern coast redwood ( S. sempervirens ). These trees could have been as tall as 60 m (200 ft) until they were killed by lahars suffocating

975-503: Is only a minor part of the geologic record, hot spring deposits are important to paleontologists because such deposits sometimes preserve more delicate plant parts in exquisite detail. These Lagerstätte deposits include the Paleozoic Rhynie Chert and East Kirkton Limestone beds, which record early stages in the evolution of land plants. Most of the color in petrified wood comes from trace metals. Of these, iron

1050-477: Is rapidly broken down by inorganic reactions with the alkali. Wood is preserved from decomposition by rapid entombment in mud, particularly mud formed from volcanic ash. The wood is then mineralized to transform it to stone. Non-mineralized wood has been recovered from Paleozoic formations, particularly Callixylon from Berea Sandstone , but this is very unusual. The petrified wood is later exposed by erosion of surrounding sediments. Non-mineralized fossil wood

1125-517: Is rapidly destroyed when exposed by erosion, but petrified wood is quite durable. Some 40 minerals have been identified in petrified wood, but silica minerals are by far the most important. Calcite and pyrite are much less common, and others are quite rare. Silica binds to the cellulose in cell walls via hydrogen bonding and forms a kind of template. Additional silica then replaces the cellulose as it decomposes, so that cell walls are often preserved in great detail. Thus silicification begins within

1200-522: Is the most important, and it can produce a range of hues depending on its oxidation state . Chromium produces bright green petrified wood. Variations in color likely reflect different episodes of mineralization. In some cases, variations may come from chromatographic separation of trace metals. Wood can also be petrified by calcite , as occurs in concretions in coal beds. Wood petrified by calcite tends to retain more of its original organic material. Petrification begins with deposition of goethite in

1275-462: Is the name given to a special type of fossilized wood , the fossilized remains of terrestrial vegetation . Petrifaction is the result of a tree or tree-like plants having been replaced by stone via a mineralization process that often includes permineralization and replacement. The organic materials making up cell walls have been replicated with minerals (mostly silica in the form of opal , chalcedony , or quartz ). In some instances,

1350-473: The Carboniferous through Permian periods seem to have favored this process. Preservation of petrified forests in volcanic ash beds is less affected by climate and preserves a greater diversity of species. Areas with a large number of petrified trees include: Lahar A lahar ( / ˈ l ɑː h ɑːr / , from Javanese : ꦮ꧀ꦭꦲꦂ ) is a violent type of mudflow or debris flow composed of

1425-581: The Philippine government were not adequate to stop over 6 m (20 ft) of mud from flooding many villages around Mount Pinatubo from 1992 through 1998. Scientists and governments try to identify areas with a high risk of lahars based on historical events and computer models . Volcano scientists play a critical role in effective hazard education by informing officials and the public about realistic hazard probabilities and scenarios (including potential magnitude, timing, and impacts); by helping evaluate

1500-677: The Florissant Fossil Bed National Monument was established after a long legal battle between local land owners and the federal government. Today, the park receives approximately 60,000 visitors a year, and is the site of ongoing paleontological investigations. The formation itself was renamed the Florissant Formation in 2001 to conform with the requirements of the North American Commission on Stratigraphic Nomenclature. In

1575-533: The Florissant beds was determined to be between 300 and 900 meters, much lower than the modern elevation of 2,500-2,600 meters. However, more recent estimates that are based on paleoflora have put the elevation in the Eocene much higher. Ranges from 1,900 to 4,100 meters have been proposed. This would indicate that global climate change, rather than tectonic uplift, would be the main cause of changing environments in

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1650-443: The Florissant. Surprisingly, no reptiles or amphibians have been recorded from Florissant, where they would have been expected. No explanation for the lack has been proposed, given the nearly 40,000 specimens from this location held by museums. The toxicity of the water due to volcanic activity could be to blame, but there are documented cases of aquatic animals in the lake. Fossil plants, and in particular their leaves, have been

1725-420: The Florissant. Of these, the beetles are the most diverse and dominate in number of specimens found as fossils. About 38% of the specimens found in the fossil beds are varieties of beetle. These fossils are aquatic and terrestrial insects, giving insight into the ecology and biology of the area. Ostracods are believed to have fed on algae on the bottom of the lake. Most of the fossil examples of ostracod come from

1800-746: The Philippines and Nevado del Ruiz in Colombia, the latter of which killed more than 20,000 people in the Armero tragedy . The word lahar is of Javanese origin. Berend George Escher introduced it as a geological term in 1922. The word lahar is a general term for a flowing mixture of water and pyroclastic debris. It does not refer to a particular rheology or sediment concentration. Lahars can occur as normal stream flows (sediment concentration of less than 30%), hyper-concentrated stream flows (sediment concentration between 30 and 60%), or debris flows (sediment concentration exceeding 60%). Indeed,

1875-533: The area was mapped by geologists for the first time. Geologists of the Hayden Survey visited the area in the early 1870s, and fossil plants from the beds were described by Leo Lesquereux , fossil insects by Samuel Hubbard Scudder , and vertebrate fossils by Edward Drinker Cope . The formation was first formally named as the Florissant Lake Beds by Charles Whitman Cross in 1894. In 1969,

1950-409: The area. The actual elevation of the Florissant area during the Eocene is still being determined. While most of the analysis using paleoflora has the area at a higher elevation than modern times, there is evidence that the elevation was as low as the earlier estimates. Petrified wood Petrified wood (from Ancient Greek πέτρα meaning 'rock' or 'stone'; literally 'wood turned into stone'),

2025-423: The beds, including a cuckoo . Most of the skeleton was lost, but there were still enough diagnostic features to identify the bird. There are also examples of rollers and shorebirds . Other birds were described in early literature from the 19th century, but the exact identification of these samples cannot be done due to lack of information. Mammals are almost non-existent in the shales, with only one specimen of

2100-475: The best ways to do this is by studying the characteristics of the leaves that have been found. By looking at the physiognomy, or analysis of gross appearance based on climatic factors, the mean average temperature (or MAT) has been estimated to be around 13 °C, much warmer than the modern MAT at Florissant of 4 °C. There have also been estimates that the MAT was between 16 and 18 °C, based on comparisons to

2175-427: The cell walls in the wood. Hemicellulose, a branched polymer of various simple sugars , makes up the majority of the remaining composition of hardwood while lignin, which is a polymer of phenylpropanes , is more abundant in softwood . The hemicellulose and lignin encrust and reinforce the cellulose microfibrils. Dead wood is normally rapidly decomposed by microorganisms, beginning with the holocellulose. The lignin

2250-461: The cell walls, and the spaces within and between cells are filled with silica more gradually. Over time, almost all the original organic material is lost; only around 10% remains in the petrified wood. The remaining material is nearly pure silica, with only iron, aluminum, and alkali and alkaline earth elements present in more than trace amounts. Iron, calcium, aluminum are the most common, and one or more of these elements may make up more than 1% of

2325-557: The cell walls, followed by deposition of calcite in the void spaces. Carbonized wood is resistant to silicification and is usually petrified by other minerals. Wood petrified by minerals other than silica minerals tends to accumulate heavy metals, such as uranium , selenium , and germanium , with uranium most common in wood high in lignin and germanium most common in wood preserved in coal beds. Boron , zinc , and phosphorus are anomalously low in fossil wood, suggesting they are leached away or scavenged by microorganisms. Less commonly,

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2400-480: The closest living relatives of the plants. There are also indications that the seasonal changes in the area were not as great as what is seen in modern times. Estimates of MAT, based on pollen, have put the temperature as high as 17.5 °C, but pollen is arguably less diagnostic than leaves. . Based on the small size and the features of the teeth, the precipitation during the late Eocene to early Oligocene has been estimated to be around 50-80 centimeters per year, with

2475-400: The composition. Just what form the silica initially takes is still a topic of research. There is evidence of initial deposition as opal , which then crystallizes to quartz over long time periods. On the other hand, there is some evidence that silica is deposited directly as quartz. Wood can become silicified very rapidly in silica-rich hot springs. While wood petrified in this setting

2550-557: The effectiveness of proposed risk-reduction strategies; by helping promote acceptance of (and confidence in) hazards information through participatory engagement with officials and vulnerable communities as partners in risk reduction efforts; and by communicating with emergency managers during extreme events. An example of such a model is TITAN2D . These models are directed towards future planning: identifying low-risk regions to place community buildings, discovering how to mitigate lahars with dams, and constructing evacuation plans. In 1985,

2625-612: The effects of volcanic activity, lahars can occur even without any current volcanic activity, as long as the conditions are right to cause the collapse and movement of mud originating from existing volcanic ash deposits. Several mountains in the world – including Mount Rainier in the United States, Mount Ruapehu in New Zealand, and Merapi and Galunggung in Indonesia – are considered particularly dangerous due to

2700-560: The end of the Cretaceous , although the exact timing of the orogeny is debated In the late Eocene to the Early Oligocene, volcanic episodes began to occur to the southwest of the Florissant area. These episodes of eruption would deposit ash and other volcanic debris on the Florissant location, and the volcanic material would be one of the most important factors in the fossilization of the plants and animals that are so abundant in

2775-422: The environment was ideal for a large range of animals to survive in the area. The great preservation of these animals gives insight into the environment that they survived in, as well as some aspects of their behavior. The invertebrate fossils of the Florissant are arthropods , such as spiders, millipedes , insects, and ostracods ; and mollusks such as clams and snails. Of these, the most significant seem to be

2850-894: The event of a Mount Rainier eruption. A lahar warning system has been set up at Mount Ruapehu by the New Zealand Department of Conservation and hailed as a success after it successfully alerted officials to an impending lahar on 18 March 2007. Since mid-June 1991, when violent eruptions triggered Mount Pinatubo 's first lahars in 500 years, a system to monitor and warn of lahars has been in operation. Radio-telemetered rain gauges provide data on rainfall in lahar source regions, acoustic flow monitors on stream banks detect ground vibration as lahars pass, and staffed watchpoints further confirm that lahars are rushing down Pinatubo's slopes. This system has enabled warnings to be sounded for most but not all major lahars at Pinatubo, saving hundreds of lives. Physical preventative measures by

2925-463: The female cones are smaller than the modern examples. There have been more than 130 species of pollen that have been identified in the shale beds at Florissant. These species represent samples from many different habitats that were located near and around the lake, as well as farther up the valley. Benthic diatoms are the dominant type of siliceous algae found in the beds. These are easy to fossilize due to their silica shells. During periods of volcanism,

3000-552: The formation is that they are not found with their legs curled in, but instead they are fully extended. This could indicate that they died in warmer temperature or acidic waters. The insects that are found in the ash-clay beds are diverse and numerous. Mayflies , dragonflies , damselflies , grasshoppers , crickets , katydids , cockroaches , termites , earwigs , web-spinners , cicadas , snake flies , lacewings , beetles , flies , mosquitoes , butterflies , moths , wasps , bees , ants , and other insects have all been found in

3075-630: The formation. The fossil bearing paper shales are intercalated with larger deposits of volcanic material. Most of the rocks that were deposited after the Oligocene and before the Pleistocene have been eroded away. Most of the remaining units are composed of clasts of weathered Pikes Peak Granite, volcanics, and mud that were transported by streams that flowed through the area. Some mammoth bones have been found within these units and have been dated to around 50,000 years old. Around 25–30 kilometers to

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3150-696: The heart of the city and surrounding areas. Over 6 metres (20 ft) of mud inundated and damaged the towns of Castillejos , San Marcelino and Botolan in Zambales , Porac and Mabalacat in Pampanga , Tarlac City , Capas , Concepcion and Bamban in Tarlac . The Bamban Bridge on the MacArthur Highway, a major north–south transportation route, was destroyed, and temporary bridges erected in its place were inundated by subsequent lahars. On

3225-458: The influxes of silica from volcanic ash lead to blooms of algae, which lead to algal mats and the exceptional preservation of the fossils. Florissant is significant in that it is one of the earliest known examples of freshwater diatoms. The majority of the animal fossils found at Florissant are invertebrates , but many specimens of vertebrates have been found. With such a large number of species identified in this location, it becomes apparent that

3300-480: The lahars killed more than 1500. The eye of Typhoon Yunya passed over the volcano during its eruption on 15 June 1991, and the resulting rain triggered the flow of volcanic ash , boulders, and water down rivers surrounding the volcano. Angeles City in Pampanga and neighbouring cities and towns were damaged by lahars when Sapang Balen Creek and the Abacan River became channels for mudflows and carried them to

3375-407: The lake. The lahars then covered the base of the redwoods that were living at the time, and the trunks of the trees became harder and fossilized. Through permineralization, the precipitates that were in the ground water flowed through the tree trunks, replacing the original matter with siliceous minerals, replacing the organic matter with silica. This process of mineralization led to the preservation of

3450-738: The late Eocene to early Oligocene, approximately 34 million years ago, the area was a lake environment with redwood trees. The basement is the Proterozoic aged Pikes Peak Granite. There is an unconformity from the Pikes Peak Granite to the next unit, the Wall Mountain tuff. The massive unconformity is due to erosion that occurred during the uplift of the modern Rocky Mountains, the Laramide Orogeny . The Wall Mountain Tuff

3525-531: The lignin may remain. Silica in the form of opal-A, can encrust and permeate wood relatively quickly in hot spring environments. However, petrified wood is most commonly associated with trees that were buried in fine grained sediments of deltas and floodplains or volcanic lahars and ash beds. A forest where such material has petrified becomes known as a petrified forest . Petrified wood forms when woody stems of plants are buried in wet sediments saturated with dissolved minerals. The lack of oxygen slows decay of

3600-676: The morning of 1 October 1995, pyroclastic material which clung to the slopes of Pinatubo and surrounding mountains rushed down because of heavy rain, and turned into an 8-metre (25 ft) lahar. This mudflow killed at least 100 people in Barangay Cabalantian in Bacolor . The Philippine government under President Fidel V. Ramos ordered the construction of the FVR Mega Dike in an attempt to protect people from further mudflows. Typhoon Reming triggered additional lahars in

3675-425: The most useful sources of information of paleoclimate during the time of deposition of the Florissant Formation. Plants have a smaller tolerance on average to climatic changes, whereas many animals can be mobile and respond to rapid seasonal or daily changes. Comparing fossil plants and leaves to modern analogs enables inferences about the climate to be made based on physiological and morphological similarities. One of

3750-487: The original structure of the stem tissue may be partially retained. Unlike other plant fossils, which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material. The petrifaction process occurs underground, when wood becomes buried in water or volcanic ash . The presence of water reduces the availability of oxygen which inhibits aerobic decomposition by bacteria and fungi. Mineral-laden water flowing through

3825-529: The overall death toll to over 25,000. Footage and photographs of Omayra Sánchez , a young victim of the tragedy , were published around the world. Other photographs of the lahars and the impact of the disaster captured attention worldwide and led to controversy over the degree to which the Colombian government was responsible for the disaster. Lahars caused most of the deaths of the 1991 eruption of Mount Pinatubo . The initial eruption killed six people, but

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3900-408: The oxygen supply to their roots. Dendrochronological examination of the tree rings has resulted in estimated ages of 500–700 years old when the trees were killed and buried. Some of the stumps belong to angiosperms . The Florissant Formation is also known for its fossilized leaves and the impressions they made. There are also specimens of fruits, seeds, cones, and flowers, which are all preserved in

3975-406: The paper shales of the formation. Most of the leaves come from trees and shrubs. Angiosperms are the dominant paleoflora, but there are also conifers present. Some of the cones, foliage, and pollen have been identified as coming from the sequoias. There are distinct differences in the fossilized Sequoia affinis material to the modern redwoods of California. The foliage in the fossils is thinner and

4050-501: The preserved carapaces, or feeding appendages. Only one species of ostracods has been described so far. Several freshwater mollusks have been identified, including freshwater and terrestrial. The most abundant mollusk that has been identified at Florissant is gastropods (snails). The vertebrate fossils in the Florissant are predominantly small fragments of incomplete bones. There have been a few described species of vertebrates, mostly fish, but also birds and mammals. The fish discovered at

4125-467: The redwoods in California grow in. The average ring width, one year of growth, is larger than the width of redwoods in central California. Towards the end of the Eocene, the global temperature began to decrease. However, this episode of global cooling is not indicated in the fossil record at Florissant. The fossilized algae and aquatic angiosperms indicate that the lake was freshwater and shallow. Near

4200-490: The replacement minerals in petrified wood are chalcocite or other sulfide minerals . These have been mined as copper ore at locations such as the Nacimiento Mine near Cuba, New Mexico . Scientists have attempted to duplicate the process of petrification of wood, both to better understand the natural petrification process and for its possible use as a ceramic material. Early attempts used sodium metasilicate as

4275-640: The rheology and subsequent behaviour of a lahar may vary in place and time within a single event, owing to changes in sediment supply and water supply. Lahars are described as 'primary' or 'syn-eruptive' if they occur simultaneously with or are triggered by primary volcanic activity. 'Secondary' or 'post-eruptive' lahars occur in the absence of primary volcanic activity, e.g. as a result of rainfall during pauses in activity or during dormancy. In addition to their variable rheology, lahars vary considerably in magnitude. The Osceola Lahar produced by Mount Rainier in modern-day Washington some 5600 years ago resulted in

4350-706: The risk of lahars. Several towns in the Puyallup River valley in Washington state, including Orting , are built on top of lahar deposits that are only about 500 years old. Lahars are predicted to flow through the valley every 500 to 1,000 years, so Orting, Sumner , Puyallup , Fife , and the Port of Tacoma face considerable risk. The USGS has set up lahar warning sirens in Pierce County, Washington , so that people can flee an approaching debris flow in

4425-691: The same time burying them in mud, which can harden to near-concrete hardness. A lahar's viscosity decreases the longer it flows and can be further thinned by rain, producing a quicksand -like mixture that can remain fluidized for weeks and complicate search and rescue. Lahars vary in speed. Small lahars less than a few metres wide and several centimetres deep may flow a few metres per second. Large lahars hundreds of metres wide and tens of metres deep can flow several tens of metres per second (22 mph or more), much too fast for people to outrun. On steep slopes, lahar speeds can exceed 200 kilometres per hour (120 mph). A lahar can cause catastrophic destruction along

4500-449: The sediments may lead to permineralization, which occurs when minerals precipitate out of solution filling the interiors of cells and other empty spaces. During replacement, the plant's cell walls act as a template for mineralization. There needs to be a balance between the decay of cellulose and lignin and mineral templating for cellular detail to be preserved with fidelity. Most of the organic matter often decomposes , however some of

4575-477: The shale units represents lacustrine environments, composed of very thin shales that are abundant in fossils, which alternate with tuffs from eruptions. The lower mudstone has been interpreted as a stream environment with the top of the unit being a lahar deposit. The mudstones were deposited on a valley floor, but not in a lake. The separation of the shale units by non-lake deposits could mean that there were two generations of lake deposits. Lahars that went through

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4650-433: The site include bowfins , suckers , catfishes , and pirate perches . Most of these were bottom dwellers, except the perches, and many were tolerant of poor water conditions. Most of the fish have been found in the same shale layers versus other shale layers. This could indicate that there were more tolerable times for fish populations over the history of the lake than other times. Three examples of birds have been found in

4725-470: The southwest, a series of stratovolcanoes, similar to modern day volcanoes like Mt. St Helens, developed and erupted periodically. Called the Guffey volcanic center, within the larger Thirtynine Mile volcanic field , the volcano had eruptions that included domes, lava flows, and pyroclastic events. Ash from these events settled throughout the area and lahars flowed down the valleys. The ash that settled created

4800-419: The spiders and insects, of which over 1,500 species have been identified in the fossil beds. Arachnids are well represented in the Florissant, mostly a large variety of spiders. There have also been possible examples of harvestmen and daddy long-legs . There may be some evidence for gall mites , but no fully identified body fossils of them have been discovered yet. One unusual aspect of the spiders found in

4875-399: The streams and shore, moisture was plentiful, allowing lush vegetation to grow. However, further up the hillsides was more dry-adapted vegetation. At the base of the valley, trees (such as sequoias) dominated the landscape. The understory of this forest would have been composed of smaller trees and shrubs. There would have been a gradual transition between the different habitats from the base of

4950-557: The stress from the volcanic episodes at the same time caused large die-offs of the local biota . As the plants and animals died off, their leaves and bodies fell into the lake and eventually large amounts of organic matter accumulated at the bottom of the lake. This process was repeated often, possibly yearly, as the runoff from rain collected in the lake, causing cyclical diatom blooms and die-offs. The diatom blooms and die-offs created layers of ash-clay deposits, called couplets, resulting in many thin layers. Each microlayer of ash and clay

5025-422: The stumps of the trees. Within the lake itself, the volcanic deposits were periodically deposited into the lake either through direct deposition or though weathering. The volcanic material was rich in silica. Living in the lake at the time were diatoms , whose shells were also composed of silica. The influx of more silica caused the diatoms to bloom in the lake. As the population of the diatoms massively increased,

5100-463: The tuff, and the lahars formed the mudstones and the conglomerates of the Florissant formation. The Florissant was deposited in a paleovalley after one of the lahars dammed it up. The resulting lake became as large as 36 km. There were two cycles of lake environments. The first one created the lower shale unit, while the second lake created the middle and upper shale units. Eventually, the volcanoes became dormant and started to erode away. Over time,

5175-404: The valley could have dammed up the valley, allowing for the creation of a lake. The middle and upper shale units were then deposited in this second generation of the lake. The caprock conglomerate was deposited as a large lahar went through the valley and accumulated down on the lake floor. The Laramide Orogeny, which created the modern Rocky Mountains, had been uplifting the area to the west since

5250-400: The valley up the hillsides, with some overlap between the two. Insects from the area indicate different habitats as well. There are exclusively aquatic insects, such as dragonflies, that would have lived their entire lives on or near the lake. Meanwhile, the bees and butterflies would have preferred more open spaces in the surrounding hillsides and meadows. Early estimates of the elevation of

5325-517: The volcano Nevado del Ruiz erupted in central Colombia. As pyroclastic flows erupted from the volcano's crater , they melted the mountain's glaciers, sending four enormous lahars down its slopes at 60 kilometers per hour (37 miles per hour). The lahars picked up speed in gullies and coursed into the six major rivers at the base of the volcano; they engulfed the town of Armero , killing more than 20,000 of its almost 29,000 inhabitants. Casualties in other towns, particularly Chinchiná , brought

5400-424: The volcanoes became so eroded that there are no more obvious signs of them on the surface. Instead, the Eocene erosional surface is the only remnant of the area's volcanoes. The volcanic material that caused so much destruction led to the preservation of the fossils within the Florissant Formation's shales and mudstones. As the ash was deposited on the landscape, it was carried by water through streams and lahars to

5475-427: The wood, allowing minerals to replace cell walls and to fill void spaces in the wood. Wood is composed mostly of holocellulose ( cellulose and hemicellulose ) and lignin . Together, these substances make up 95% of the dry composition of wood. Almost half of this is cellulose, which gives wood much of its strength. Cellulose is composed of long chains of polymerized glucose arranged into microfibrils that reinforce

5550-494: Was compacted by overlaying sediments to create "paper shales" (usually between 0.1 and 1.0 mm thick). Within these paper shales the best preserved fossils can be found in the formation. Based on this information, it has been estimated that the lake could have lasted 2,500 to 5,000 years, if the diatom couplets represent annual cycles. There is a large diversity of plants in the beds of the Florissant Formation, ranging from large redwoods to microscopic pollen. The petrified forest

5625-427: Was deposited as a result of a large eruption from a distant caldera . The Florissant Formation itself is composed of alternating units of shale, mudstone, conglomerate, and volcanic deposits. There are six described units within the Florissant Formation. In order from bottom to top: the lower shale unit, lower mudstone unit, middle shale unit, caprock conglomerate unit, upper shale unit, and the upper pumice unit. Each of

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