When was mt pelee formed

The picture on the right is a closer view of the U1 lower layer, sampled in the northern part of St Pierre yellow star in Figure 2 where the deposit is directly in contact with the pavement of the city. The white scale bar is 20 cm long. Using a variety of indicators, the local direction of propagation of the ash-cloud surge was reconstructed.

Lacroix estimated the direction of the ash-cloud surge to be parallel to Victor Hugo Street in St Pierre red line in Figure 3 using the N-S orientation of the remaining standing walls and the N-S alignment of the dead bodies in the streets. From measurements in cross-bedded deposits, Fisher et al. However, authors disagreed on the direction, either being from north to south or from the block-and-ash flow to the southwest.

The dynamic pressure of the ash-cloud surge can be estimated from its effects on buildings, especially in St Pierre, following the study of Jenkins et al. Comparing the damage at Merapi volcano Jenkins et al. Based on the dynamic pressure calculation method of Jenkins et al. The rest of the city, only partially damaged, was exposed to a dynamic pressure less than 2 kPa, as deduced from the presence of standing walls in the Center and Mouillage districts, and then pressure drops under 1 kPa in the southernmost part of the city attested by the standing cathedral towers in Figures 3C,D.

Following these extensive field studies, various interpretations of the May 8th, pyroclastic current source conditions and its internal dynamics have been inferred.

We regroup them in two main theories:. This concentrated flow is thought to have been generated from the collapse of a short column formed by an intra-crater vertical explosion Fisher et al. This idea came from Hill who initially located the source to be approximately at Morne Lenard 2. Later, Fisher et al. Because of the two differing interpretations outlined above, the exact nature of the eruption source conditions i. Moreover, despite insightful descriptions of the pyroclastic current deposits, the total deposit volume is still missing.

No study has estimated the volume of each separate current May 8th and 20th, June 6th, or August 30th as the field studies conducted following the eruption compiled the effects of the individual currents. Nevertheless, the total volume of the May 8th pyroclastic current, as well as the volume portions of the block-and-ash flow and ash-cloud surge components, are still unknown.

The numerical model used in this study is the newer two-layer version of VolcFlow, which was developed to more accurately simulate the dynamics and extent of pyroclastic currents Kelfoun, This version was used to simulate: i block-and-ash flows and ash-cloud surges at Merapi Volcano Kelfoun et al. The code is based on two coupled, depth-averaged currents: one for the basal concentrated flow also called block-and-ash flow in this study and one for the overriding ash-cloud surge.

The dynamics of each current are modeled using depth-averaged equations of mass and momentum balance in the x and y directions. The ash-cloud surge requires an additional equation, as density varies in time and space due to loss of mass through sedimentation. The two layers are then coupled and exchange mass and momentum following two exchanges laws arrows in Figure 5.

The complete description of the physical model, the equations, and all the parameters used in VolcFlow are summarized in Supplementary Material. The reader can also refer to Kelfoun and Gueugneau et al. Figure 5. Sketch of the general model of the two-phase version of VolcFlow Kelfoun, To simulate stresses applied to the concentrated flow during transport using a depth-averaged approach, the plastic rheological law is used, involving a constant retarding stress T see Supplementary Material.

Despite the lack of physical explanation for applying this rheology to pyroclastic currents, several studies have demonstrated the ability of the constant retarding stress to reproduce various features of such currents and their deposits Kelfoun et al. The ash-cloud surge is simulated as a turbulent continuum that loses momentum due to turbulent drag stresses. To perform the numerical simulations, the Observatoire Volcanologique et Sismologique de Martinique provided a 5 m resolution LiDAR DEM of Martinique Island, constructed in , that was down-sampled to 10 m to save computational time.

Despite the current debate regarding the source conditions that generated the May 8th pyroclastic current i. The crater shape seems to have reoriented the expansion of the fragmented material into this V-shaped outlet.

This caldera is approximated in the DEM by a bowl-shape of m wide for m deep, and centered roughly on the lava dome, as illustrated in Figure 6. With this modification, the outlet on the southern part of the crater rim is reconstructed at the same location as it was prior to May Figure 6. This simplified source can thus model the collapse of either a short column or a lava dome. The resulting overflow is self-regulated and dependent on the supply rate in the crater, as illustrated in Figure 6C blue curve.

Because of the synthetic crater, a large part of the deposit volume remains stuck inside the depression and does not feed the simulated pyroclastic current.

Therefore, we distinguished the volume of material supplied in the crater V ini to the total volume of deposit V that escaped through it to constitute the pyroclastic current. Figure 6. The red line in B highlights the position of the newly formed V-shape crater outlet. Table 2. Input parameters for the best-fit VolcFlow simulation presented in Figure 7.

Only the scenario of Fisher et al. Consequently, the higher the block-and-ash flow velocity, the higher the surge production. To model such complex dynamics of the pyroclastic current, the code requires 11 input parameters for each simulation see Supplementary Material.

Each of these parameters has a clear influence on the morphology of the simulated flows and on the resulting deposit footprint, which makes it relatively easy to estimate the best fit. To better see the influence of each parameter on the model dynamics, the reader can refer to Kelfoun et al. To quantitatively evaluate the simulation results and to identify a best fit simulation, the differences between simulated and observed flows are calculated using validation metrics, which compare areas inundated by the simulation Asim to the real deposit Aobs.

The matching area between simulated and observed flows is called true positive TP , the over-simulated area is called false positive FP and the missing simulated area is called false negative FN. Three coefficients were used:. The reader can refer to Charbonnier et al. Values obtained for the best-fit simulation are included in Table 3. Table 3. Values of validation metrics used for evaluating the best-fit simulation. For more than a hundred simulations of 10—20 h each, seven unconstrained input parameters Table 2 were adjusted to obtain a combination of highest possible values for the three metrics, obtained for the 90th simulation.

The volume of material in the crater and the supply duration are first adjusted by matching the general aerial distribution and thicknesses of the simulated deposits to the real one. Then, the surge characteristics production and sedimentation parameters as well as the constant retarding stress of the concentrated flow are adjusted to find the combination of highest values for the three metrics for the area covered by the ash-cloud surge only.

The choice to focus primarily on the ash-cloud surge was motivated by the fact that: 1 its extent and limits, as extracted from the field, are based on robust evidence and therefore only contain small uncertainties, and 2 it covered a much larger area than the block-and-ash flow, restricted to valleys. However, the maximum runout in the south of St Pierre is underestimated where the simulated ash-cloud surge traveled m less that the real flow.

Also, a large part of the area inundated by the ash-cloud surge around the northern part of the crater is not reproduced by the simulations. Since the location of the initial mass flux in the simulations was set to be in the southern crater outlet, the simulated ash-cloud surge derived from the block-and-ash flow in the proximal area was unable to spread northward and inundate that part of the crater.

Figure 7. Results of the best fit simulation obtained using the input parameters presented in Table 2. A Final distribution of the simulated deposits from the best-fit simulation, which include the extent of the simulated ash-cloud surge green color scale for the thickness and the simulated block-and-ash flow pink color scale. For ease of comparison, outlines of the observed ash-cloud surge and block-and-ash flow, as extracted from the field, have been added with a white and black outline, respectively.

B—E Sequence of four snap shots of the best-fit simulation at 30, , , and s after the mass starts to overflow through the crater outlet, showing the propagation of the flows overlain on the DEM. Comparisons between the simulated surge deposit thicknesses with those measured at 20 locations in the field Bourdier et al.

Surge velocities are either in good agreement or underestimated by a factor of 3, depending on the reference value taken Table 3 but are within the typical range of 40—90 m s —1 for ash-cloud surge estimations elsewhere Calder et al.

Indeed, the simulated flow inundated an area similar to the real flow with a model precision coefficient of The simulated block-and-ash flow travels at an average velocity of 19 m s —1 , relatively common for this type of flow, as described elsewhere Calder et al.

Figure 8 presents the maximum dynamic pressure and the mean direction of the ash-cloud surge extracted from the best-fit simulation. In VolcFlow, the dynamic pressure P dyn is calculated following Valentine :. Figure 8. Map of the maximum dynamic pressure and a mean direction of the ash-cloud surge from the best fit simulation. The distribution of the dynamic pressure is shown as a color scale, and isobar lines indicate the 1,2 and 3 kPa blue, green and yellow lines, respectively pressure fields.

The average direction of the current is represented by white arrows, whose lengths correspond to the velocity of the ash-cloud surge, calculated from the center of the arrow. Values gradually decrease from more than 5 kPa toward the block-and-ash flow to a few Pa only toward the edges.

This pattern was also observed at Merapi volcano by Jenkins et al. The mean direction of the simulated surge is radially dispersed around the block-and-ash flow and perfectly matches the direction measured in the field by Fisher et al.

However, the model does not match the backward direction measured by Fisher et al. Toward the east, especially in the St Pierre area, flow directions slowly change from south to southeast as the simulated surge expanded eastward. The same observation can be made on the western side of the area inundated by the surge with a flow direction that changes from southwest to west.

The passage of the simulated ash-cloud surge over the flat sea surface promotes its lateral spreading as it covers a larger area to the west of St. To better investigate the behavior of the simulated ash-cloud surge toward St Pierre, Figure 9A shows a snapshot of the simulated flow dynamics in this area over the DEM while Figure 9B superimposes these simulation results and field observations over the topographic map of St Pierre in from Lacroix The external, low dynamic pressure zone of the simulated surge with a maximum pressure of 1.

Thus, the dynamic pressure in St Pierre seems to be underestimated by the model compared to field observations. In this area, the surge direction changes from southeast to south as it propagates toward the southern part of the city Figures 7A,B , matching approximately the direction of the Victor Hugo street red line as observed by Lacroix However, the mean direction of the simulated surge does not match the surge direction measured in Fort Cemetery by Boudon and Lajoie In summary, after entering the sea at Fort district, the simulated surge is first deflected to the east toward St Pierre, and then further deflected to the south by the hills on the east of St Pierre south of Morne Abel, Figure 8.

The direction of the simulated surge seems to be highly variable when it passes through St Pierre due to high turbulence induced by the complex pattern of the city infrastructures. Figure 9. When the simulated block-and-ash flow entered the sea, it formed unrealistic thick and large lobes Figure 7. Focusing all the mass through the crater outlet as the primary source condition for our simulations, as previous workers have commonly hypothesized from field observations, results in good correlations with the real event.

The resulting self-regulated volume rate Figure 6 , generated by passive overflowing of the mass through the lowest elevated part of the crater rim, produces a realistic simulated pyroclastic current.

The direction of the ash-cloud surge seems to corroborate quite well with the field direction measurements and the damage in St Pierre.

However, simulations did not reproduce the up-valley movement of the surge at Fond Canonville, inferred by Fisher et al. Charland and Lajoie questioned the reliability of the flow directions measured by Fisher et al. But beyond these conflicting measurements, the landward flow direction obtained by Fisher et al.

Unfortunately, if such a process had occurred, our simulations did not capture it because VolcFlow does not model such flow temperature and energy variations. While the deposit extent and paleo-current directions are well reproduced by our simulations, the dynamic pressure seems to be underestimated. Given the equation used here to calculate the dynamic pressure Eq. Simulated flow velocities seem to be accurate if we compare them with the field estimations from Fisher et al.

Underestimation of the dynamic pressure could also be explained by an underestimation of the surge density at the base of the flow. In fact, the shallow-water modeling approach used in VolcFlow implies the use of an averaged density across the entire current depth, which provides accurate reproduction of the general surge dynamics but constitutes an important simplification from natural density-stratified surges Valentine, Therefore, the actual density at the base of surges the part that interacts with buildings is much higher than a depth-averaged value.

This density difference could potentially explain the resulting underestimation of the dynamic pressures in our simulations. In order to reproduce the actual runout of the ash-cloud surge, the particle drag coefficient C d used in our simulations had to be set to an unrealistically high value see Table 2.

In fact, the chosen value of 35 does not match any previous estimation of this coefficient for volcanic particles 0. C d has been tuned in our model because it is the only parameter linked to the settling velocity Eq. With a smaller settling velocity, the simulated ash-cloud surge settles much slower, keeping particles in suspension for a longer time, and subsequently covers a larger area before becoming buoyant. Therefore, some process seems to have hindered sedimentation in the May 8th pyroclastic current.

A similar process has already been inferred for the simulation of the November 5th, pyroclastic current at Merapi by Kelfoun et al. Different hypotheses are proposed to explain the hindering of the sedimentation: i if the base of the May 8th, ash-cloud surge was relatively dense, as suggested by the high dynamic pressures obtained from field observations, particle settling in the density-stratified surge could have been reduced and particles transported further away i.

The factor of 30 obtained for the best-fit value of C d could be applied to the surge density instead, thus giving similar modeling results. Moreover, the resuspension of soft material i. Further model development is needed to include air entrainment in VolcFlow and to investigate whether this process has a significant influence on the dynamics of two-layer, depth-averaged simulated currents, as recently proposed by Shimizu et al.

The model of Fisher et al. Instead, the two different layers of the simulated pyroclastic current i. Indeed, the simulated surge spreads radially around the crater without following the southward spreading of the block-and-ash flow.

Moreover, the shape of the simulated ash-cloud surge area differs from the pear-like shape characterizing our best-fit simulation as well as the May 8th, surge area Figure 8. At that time Mont Pelee was a forested volcano with a flat-topped summit. Residents and officials of St. Pierre, in the foreground 7. Pelee had not erupted since , and only minor phreatic eruptions had occurred then. From the collection of Maurice and Katia Krafft.

Prior to the eruption, St. Pierre was the largest and most beautiful city of the Lesser Antilles. The forested slopes of the seemingly benign Mount Pelee provided a scenic backdrop to the thriving commercial center on the NW coast of Martinique.

The last eruption a half-century earlier had been a modest one, and even after the first explosions began on April 23, there was little concern. No volcanological studies had been made, and official statements of reassurance kept most residents in the city until the devastating eruption of May 8. One of the most dramatic events following the devastating eruptions of Mount Pelee in Martinique was the growth of a towering spine on the summit lava dome. It began to rise above the dome on November 3, By May 31, , the spine reached a height of m above the dome, temporarily creating a m-high peak at the summit.

It then slowly disintegrated and was gone by the end of the eruption. This March 11, , photo shows the spine near its peak height, with a smoothly extruded eastern side. Photo by A. Lacroix, from the collection of Maurice and Katia Krafft.

Slow, piston-like extrusion of a solidified portion of a lava dome sometimes produces vertical lava spines that rise above the surface of the dome. The world's largest known spine rose to a maximum height of m, more than twice that of the Washington Monument, at Mount Pelee on Martinique in Growth of the spine began in November and reached its maximum on May 31, It slowly disintegrated and was gone by the end of the eruption two years later.

This photo was taken on March 15, A pyroclastic flow, similiar to the one that destroyed the city of St. Pierre on Martinique on May 8, , sweeps down the flanks of Mount Pelee volcano on December 16, A towering column of ash and steam rises above the advancing pyroclastic flow, which was formed by collapse of gas-rich rocks on a growing lava dome in the summit crater. The May 8 pyroclastic flow was substantially larger than this one, and would have covered an area wider than the entire shoreline of this photo.

The devastated city of St. Pierre lies in ruins after a catastrophic eruption on 8 May , in which pyroclastic flows and surges swept over the city, killing 28, people. The high-temperature pyroclastic surges devastated a 58 sq km area SW of the volcano and swept out to sea, capsizing all but two ships in the harbor.

This March photo from the south shows Mount Pelee towering over the remnants of the city, capped by a dramatic lava spine that grew above the summit lava dome. A pyroclastic flow produced by the collapse of a growing lava dome in the summit crater, sweeps down the SW flank of Mount Pelee on 1 January Small pyroclastic flows continued for 16 months following the catastrophic eruption of 8 May , that destroyed St. A second large pyroclastic flow, comparable in size to that of 8 May, devastated the SE flank on 30 August, killing an additional people.

The frequency of pyroclastic flows diminished after September , but they continued at longer intervals until October Photo by Hayot, from the collection of Maurice and Katia Krafft. Pierre on the coast at the left , which the volcano destroyed during a catastrophic eruption in The modern volcano was constructed on the rim of a large SW-facing horseshoe-shaped caldera whose northern wall is the ridge in the shadow on the left horizon.

Photo by Richard Fiske, Smithsonian Institution. This procedure, sometimes referred to as "dry tilt," detects deformation of the volcano that often precedes an eruption by measuring the precise differences in elevation between two stadia rods placed on fixed points. This technique is part of monitoring efforts by the observatory to help detect future eruptions of this scenic, but deadly volcano. Photo by Lee Siebert, Smithsonian Institution.

This photo portrays an unusual combination of geology and history. The light-colored deposits in this outcrop south of St. Pierre are pyroclastic-flow deposits similar to those of eruptions that destroyed the city in The abundant large holes in the outcrop are not a volcanological phenomenon, but were produced by cannon balls blasted into the unconsolidated deposit during British-French wars for control of the island of Martinique.

The lava dome at the left, seen from the east rim of the crater, was formed during an eruption that began in The vegetated knob halfway down the right skyline is a lava dome from the eruption. The eruption was similiar to that of , but smaller in scale. After explosive removal of part of the dome, growth of a new dome began in January Pyroclastic flows accompanied dome growth until the end of Photo by William Melson, Smithsonian Institution. Pierre in northern Martinique a century after the catastrophic eruption that destroyed the city in Lava domes formed during the eruption and one in form the present summit, which was constructed within a large scarp visible on the lower left horizon that formed when the volcano collapsed about years ago.

This prison cell in the city of St. Devastating pyroclastic flows and surges swept down the SW flank of the volcano early in the morning and destroyed the city, killing 28, people in the world's deadliest eruption of the 20th century.

Photo by Paul Kimberly, Smithsonian Institution. The area beyond the grassy knoll was part of the first portion of the ancestral volcano that underwent massive edifice collapse more than , years ago.

This massive collapse produced a 25 cu km debris avalanche that swept into the Caribbean Sea up to 70 km from the coastline. The steep-sided grassy knob in the right foreground is part of the Aileron lava dome, which formed during an eruption about years ago.

This view looks to the SE towards the town of Morne Rouge left-center , which was devastated by pyroclastic flows during the eruption. The Pleistocene Piton du Carbet volcano lies in the clouds on the right-center horizon. The steep-sided lava dome at the left is Aileron, which was formed about years ago.

The eastern rim of l'Etang Sec, the current summit crater, cuts horizontally across the photo at the upper right in front of the dome on the right horizon. The and lava domes fill much of this crater. The town with reddish roofs at the far right is Morne Rouge, affected by pyroclastic flows from the eruption.

The modern volcano was constructed within a scarp produced by collapse of the volcano about years ago. The irregularity on the right-hand flank is part of the eastern summit crater rim and the Aileron lava dome, which erupted about years ago. The lava dome fills much of the l'Etang Sec summit crater, as seen here from Morne Macouba, north of the summit.

Following the catastrophic eruption on May 8, , rapid growth of a summit lava dome began; it reached m height by July 6. Intermittent explosive activity continued until October 31, and lava dome growth continued on a diminishing scale until October 5, The famous spine at one point rose to m, m above the current summit the lava dome , before it crumbled away.

GVMID should provide a snapshot and baseline view of the techniques and instrumentation that are in place at various volcanoes, which can be use by volcano observatories as reference to setup new monitoring system or improving networks at a specific volcano.

These data will allow identification of what monitoring gaps exist, which can be then targeted by remote sensing infrastructure and future instrument deployments. Volcanic Hazard Maps The IAVCEI Commission on Volcanic Hazards and Risk has a Volcanic Hazard Maps database designed to serve as a resource for hazard mappers or other interested parties to explore how common issues in hazard map development have been addressed at different volcanoes, in different countries, for different hazards, and for different intended audiences.

In addition to the comprehensive, searchable Volcanic Hazard Maps Database, this website contains information about diversity of volcanic hazard maps, illustrated using examples from the database.

This site is for educational purposes related to volcanic hazard maps. Hazard maps found on this website should not be used for emergency purposes. For the most recent, official hazard map for a particular volcano, please seek out the proper institutional authorities on the matter. The next morning, residents found birds that had plummeted from the air, weighted down by ash, and a steamer captain noticed dead fish floating in the sea, possibly killed by the shockwave of a submarine earthquake.

Over the following days, the mountain continued to fume, driving terrified people from the countryside into St. Pierre, which the newspapers reported was safe. No one suspected that these convulsions stemmed from magma rising from the bowels of the volcano and affecting groundwater.

Pierre, in a letter to her sister. A devastating mixture of mud and hot water, the slide destroyed a sugar processing plant on the coast, killing almost two dozen people.

The debris then spilled into the ocean, producing a 3-meter-high tsunami that inundated St. Perhaps most horrifying of all, though, was the plague of insects and snakes that slithered down from the mountain, disturbed by its paroxysms. Among the invaders were gigantic centipedes and deadly 2-meter long pit vipers, which claimed the lives of hundreds of livestock and about 50 people, according to some accounts. Soldiers shot the serpents in the streets in what would turn out to be a futile effort to protect the people of St.

On May 6, blue flames heralded the arrival of magma in the crater as a lava dome poked above its rim. On May 7, the mountain sputtered and a volcano on neighboring St. Vincent exploded, killing 1, people. The authorities, however, insisted there was nothing to fear. Rue Victor Hugo, one of the principal business streets in St. Credit: both: Library of Congress.

Moments later, all but a handful of its nearly 30, residents were dead, including the governor, who had come with his family to reassure the population. Most of the victims perished from suffocation and burns that scorched their skin and lungs. Subsequent analyses based on burnt wood yielded temperature estimates suggesting the gas cloud was between and degrees Celsius.

The explosion leveled the town, hurling massive stone statues several meters from their perches — implying the cloud reached speeds exceeding meters per second — and sparing only some walls oriented parallel to the blast. For days afterward, St.