What kind of topography does a volcano have

Bacteria forming microbial mats under the water are responsible for the coloration often seen in hot springs. Different species, with different colors thrive at different temperatures. A geyser results if the hot spring has a plumbing system that allows for the accumulation of steam from the boiling water. When the steam pressure builds so that it is higher than the pressure of the overlying water in the system, the steam will move rapidly toward the surface, causing the eruption of the overlying water.

Some geysers, like Old Faithful in Yellowstone Park, erupt at regular intervals. The time between eruptions is controlled by the time it takes for the steam pressure to build in the underlying plumbing system. Plateau or Flood basalts are extremely large volume outpourings of low viscosity basaltic magma from fissure vents. The basalts spread huge areas of relatively low slope and build up plateaus.

The only historic example occurred in Iceland in , where the Laki basalt erupted from a 32 km long fissure and covered an area of km 2 with 12 km 3 of lava. As a result of this eruption, homes were destroyed, livestock were killed, and crops were destroyed, resulting in a famine that killed people. Volcanoes and Plate Tectonics.

In the discussion we had last lecture about how magmas form, we pointed out that since the upper parts of the Earth are solid, special conditions are necessary to form magmas.

These special conditions do not exist everywhere beneath the surface, and thus volcanism does not occur everywhere. If we look at the global distribution of volcanoes we see that volcanism occurs four principal settings.

Along divergent plate boundaries, such as Oceanic Ridges or spreading centers. In areas of continental extension that may become divergent plate boundaries in the future. Along converging plate boundaries where subduction is occurring. And, in areas called "hot spots" that are usually located in the interior of plates, away from the plate margins. Diverging Plate Margins Active volcanism is currently taking place along all of oceanic ridges, but most of this volcanism is submarine volcanism and does not generally pose a threat to humans.

One of the only places where an oceanic ridge reaches above sea level is at Iceland, along the Mid-Atlantic Ridge. Here, most eruptions are basaltic in nature, but, many are explosive strombolian types or explosive phreatic or phreatomagmatic types. As seen in the map to the right, the Mid-Atlantic ridge runs directly through Iceland. All around the Pacific Ocean, is a zone often referred to as the Pacific Ring of Fire, where most of the world's most active and most dangerous volcanoes occur.

The Ring of Fire occurs because most of the margins of the Pacific ocean coincide with converging margins along which subduction is occurring.

These are all island arcs. Hot Spots Volcanism also occurs in areas that are not associated with plate boundaries, in the interior of plates. These are most commonly associated with what is called a hot spot. Hot spots appear to result from plumes of hot mantle material upwelling toward the surface, independent of the convection cells though to cause plate motion.

Hot spots tend to be fixed in position, with the plates moving over the top. As the rising plume of hot mantle moves upward it begins to melt to produce magmas. These magmas then rise to the surface producing a volcano. But, as the plate carrying the volcano moves away from the position over the hot spot, volcanism ceases and new volcano forms in the position now over the hot spot.

This tends to produce chains of volcanoes or seamounts former volcanic islands that have eroded below sea level. Volcanism resulting from hotspots occurs in both the Atlantic and Pacific ocean, but are more evident on the sea floor of the Pacific Ocean, because the plates here move at higher velocity than those under the Atlantic Ocean.

A hot spot trace shows up as a linear chain of islands and seamounts, many of which can be seen in the Pacific Ocean. The Hawaiian Ridge is one such hot spot trace. Here the Big Island of Hawaii is currently over the hot spot, the other Hawaiian islands still stand above sea level, but volcanism has ceased.

Northwest of the Hawaiian Islands, the volcanoes have eroded and are now seamounts. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

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A volcano is defined as an opening in the Earth's crust through which lava, ash, and gases erupt. The term also includes the cone-shaped landform built by repeated eruptions over time.

Teach your students about volcanoes with this collection of engaging material. Creating models of how a material flows over the ground is very important to understand volcanic hazards.

These models use DEMs as the ground surface for computer simulations of pyroclastic flows, debris avalanches, lahars, floods, and fluvial sediment transport. The models allow scientists to produce volcanic hazard maps, predict flooding caused by rain, snowfall and lake-breakouts, and reduce the impacts from sedimentation build up in rivers and streams. In a process called photogrammetry , VHP scientists take overlapping digital photographs of a volcano, which can be taken either from the air or ground.

Using recent advances in camera and computer technology these images are used to build DEMs quickly and accurately. The method is akin to the older technique of using analog stereo cameras and comparing overlapping pairs of aerial photographs taken at the same time. Collecting and processing photographs to create DEMs can be done with relatively low cost and in near real-time minutes to hours , which is an advantage when monitoring volcanic activity. Lidar images of Shastina cone, west flank of Mount Shasta, California.

Inflation or deflation of a magma reservoir is commonly modeled analytically using a point source Mogi, , where the orientation of the displacement field at the surface varies with horizontal distance from the source. The point source approximation is valid for a spherical source where the source radius is small with respect to the distance from that source. Addressing the influence of topography, Cayol and Cornet showed that displacement produced by reservoir pressure is greater at lower elevation, where the surface is closer to the source.

Delving further, Ronchin et al. Through numerical modeling, they showed that the maximum displacement is produced where the surface is perpendicular to a line between the surface and source, where the exposure to the pressure source is greatest. Hence, tilt generated by a point or spherical source is influenced by the slope angle. Beauducel and Carbone suggested that tilt induced by a spherical pressure source is greater where the slope of the edifice is steeper.

This, unsurprisingly, is as previously shown for a purely horizontal displacement field. The surface directly above a point source in an elastic half-space is pushed vertically upwards as pressure increases, as the surface is perpendicular to the displacement field. Moving horizontally away from this point, the surface rotates outwards, away from the source, which we define as a positive radial tilt. McTigue and Segall showed that where the relief of the edifice is considerable, such that the surface vertically above the source is further from the source than a point down slope, the surface rotates inwards, hence a negative radial tilt is produced.

In this case, the amplitude of displacement is greater at a point down slope than directly above the source. Whilst this relationship has been examined for a point source, the topographic effect on tilt produced by conduit pressure or shear stress has not been investigated. We include a volcanic edifice with a Gaussian slope, where the elevation z is calculated as. Roller boundary conditions that allow vertical motion only are applied to the lateral model boundaries.

The base of the model is fixed in all directions. The model is extended to a radius of 40 km and a depth of 50 km to avoid numerical effects from these boundary conditions. The surface may deform freely. A spatially-variant triangular mesh is used, that allows complex geometries to be suitably meshed easily. A finer mesh is used in the upper 3 km below the surface to a horizontal distance of 10 km, where the modeled solution is examined, and thus a higher degree of accuracy is required Figure 2D.

A minimum element size of around 30 m is used within this region. A sensitivity analysis was necessary to ensure that a sufficiently fine mesh was used, until the solution was consistent if the mesh was refined further.

The Young's modulus and Poisson's ratio of the medium are set at 1 GPa and 0. The numerical models were benchmarked against the analytical solution for a Mogi source. Figure 2. The height of the Gaussian-sloped volcano is varied. D Model setup. A high resolution mesh is used to a depth of 3 km below the surface, to a horizontal distance of 10 km, with a minimum element size of around 30 m. For both a shear stress or a conduit pressure source, the strongest tilt signal can be seen close to the conduit while it decreases with increasing distance Figure 2.

The influence of the relief on tilt produced by shear stress appears to be minimal, and the resulting tilt is always positive, irrespective of the relief. In the absence of relief, a negative radial tilt is induced by conduit pressure at all locations.

However, where the relief is considerable, such that the component of the displacement pushing the surface perpendicularly outwards decreases with increasing distance from the conduit, a positive radial tilt is modeled at intermediate distances from the conduit. Here, we must consider how both the total displacement, and the alignment of the displacement field with the surface Figure 3 , vary with distance from the conduit.

Figure 3. Deformation field produced by overpressure of the conduit for a suite of values for the edifice relief. In each case the pressure source extends from the surface to 5 km below. The arrows depict the amplitude and orientation of the displacement field at each point.

To investigate the effect of local topography on tilt, we introduce breaks in slope into our model Figure 4. A tapering feature was used to avoid sharp edges at the breaks in slope. We include one slope facing away from the center of the model, hereon referred to as the proximal slope.

This is opposed by a slope facing toward the center of the model, hereon referred to as the distal slope. With this pair of opposing slopes, we attempt to represent topographic features such as cliffs and valleys. We focus on this morphology, as Johnson et al. The resolution of the triangular mesh is increased in the close vicinity of each break in slope, to a minimum element size of around 20 cm. The location of these opposing slopes is varied.

Figure 4. Two opposing slopes introduced onto the Gaussian-sloped edifice, in A 3D and B 2D axisymmetric space. Since the topographic effect on tilt is predominantly limited to the extent of the topographic feature Harrison, , the topographic effect of each break in slope can be considered in isolation.

Thus, the topographic effect of a range of features can be inferred based on our models, such as cliffs, ridges, and valleys. Whilst Harrison investigated how tilt induced by earth tides is affected by the inclusion of a cavity or valley, the topographic effect on tilt generated by volcanic sources may be considerably different, due to 1 differences in the orientation of the deformation field with respect to the surface, and 2 the spatial extent of deformation is much smaller for shallow volcanic sources than generated by earth tides, and can be similar to the scale of typical topographic features found at volcanoes Figure 2.

We introduce the following parameters that are used in the following sections:. For a spherical pressure source, the total displacement decreases with increasing distance from the source. For an edifice with a relief of 3 km as shown here, the summit is not the closest point to the source.