Why are Stratovolcanoes more dangerous than shield volcanoes?

Due to the higher viscosity of magmas erupted from these volcanoes, they are usually more explosive than shield volcanoes. Stratovolcanoes sometimes have a crater at the summit that is formed by explosive ejection of material from a central vent.

Why are stratovolcanoes the most dangerous?

Stratovolcanoes are the most dangerous volcanoes to humans and animals because they are very explosive, producing toxic gas and flying volcanic fragments. Explosive volcanic eruptions, which are common to stratovolcanoes, pose serious threats to aviation travel.

Why are composite volcanoes more dangerous than shield volcanoes?

Composite volcanoes have the following characteristics: Andesitic magma, which is lower in temperature, has more silica and a lot of dissolved gases and is more likely to explode when it reaches the surface. Acidic lava, which is very viscous (sticky).

Why are shield volcanoes less dangerous?

The lava flow from a shield volcano eruption is largely composed from basaltic magma. The lava features a low viscosity and erupts in a relatively gentle stream. Therefore, shield volcano eruptions generally do not pose a threat to human lives, as the lava flow is easy to predict and avoid.

Which is more dangerous shield or composite volcanoes?

When comparing the two volcano types, shield and composite, it is obvious that although the shield volcanos are more massive (see Figure 9.9), they are far less dangerous to the population than the smaller composite volcanoes.

What are the hazards of stratovolcanoes?

Stratovolcanoes (also known as composite volcanoes) are built of successive layers of ash and lava. The magma (molten rock) within the volcano is viscous and often contains trapped gas, causing explosive eruptions. The clouds of ash from the volcanic eruptions present a hazard to aviation.

What is the difference between Shield and stratovolcanoes?

Stratovolcano. Stratovolcanoes have relatively steep sides and are more cone-shaped than shield volcanoes. They are formed from viscous, sticky lava that does not flow easily. The lava therefore builds up around the vent forming a volcano with steep sides.

Why are stratovolcanoes more explosive?

These more viscous lavas allow gas pressures to build up to high levels (they are effective “plugs” in the plumbing), therefore these volcanoes often suffer explosive eruptions.

What types of hazards are associated with shield volcanoes and stratovolcanoes?

Lava flows, pyroclastic density currents, landslides, and rockfalls seldom travel far beyond a stratovolcano’s base. At the volcano, tephra fall will include large hot blocks of rock, and dangerous concentrations of volcanic gases can collect in caves.

What is the main hazard of a shield volcano?

Hazards posed by shield volcanoes include lava flows, near-vent ballistics and pyroclasts, phreatomagmatic explosions, and degassing.

What type of lava erupts from stratovolcanoes?

The lava flowing from stratovolcanoes typically cools and hardens before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma.

Are stratovolcanoes and composite volcanoes the same?

Stratovolcanoes are also called composite volcanoes because they are built of layers of alternating lava flow, ash and blocks of unmelted stone, according to the U.S. Geological Survey. They are larger than cinder cones, rising up to 8,000 feet (2,438 m).

What makes a shield volcano A shield volcano?

A shield volcano is a type of volcano named for its low profile, resembling a warrior’s shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava erupted from a stratovolcano.

Which of these are features of most stratovolcanoes?

The characteristics of a stratovolcano are as follows: The eruptions are very violent and explosive, hurling volcanic bombs. They have steep sides as high as 7,000 feet, and the shape is a symmetrical cone. It consists of alternating layers of lava and ash.

Why do stratovolcanoes form at convergent boundaries?

Composite volcanoes are common along convergent plate boundaries. When a tectonic plate subducts, it melts. This creates the thick magma needed for these eruptions. The Pacific Ring of Fire is dotted by composite volcanoes.

Why does subduction lead to volcanic activity?

At a subduction zone an oceanic crust is pushed under the continental crust. As the oceanic crust is pushed under the continental crust it is subjected to heat and pressure. The heat and pressure causes the crust to melt and become magma. … When the magma reaches the surface it creates a volcano.

How does subduction lead to volcanic activity?

ii) Subduction leads to volcanic activity because as one plate is subducted under another over a hotspot, the plate melts into magma. The hotspot pushes the magma upward until the magma meets the surface and releases out of a volcano.

Why do mafic lavas produce shield shaped volcanoes?

The lava that creates shield volcanoes is fluid and flows easily. The spreading lava creates the shield shape. Shield volcanoes are built by many layers over time and the layers are usually of very similar composition. The low viscosity also means that shield eruptions are non-explosive.

How would you differentiate among shield volcanoes composite volcanoes and pyroclastic cones in the field?

Composite volcanoes are tall, steep cones that produce explosive eruptions. Shield volcanoes form very large, gently sloped mounds from effusive eruptions. Cinder cones are the smallest volcanoes and result from accumulation of many small fragments of ejected material.

Why does high silica magma tend to form volcanic domes with steep sides?

Silica-rich magmas are far less fluid. They often stop moving before they reach the surface. If they do reach the surface, they ooze slowly, like toothpaste squeezed out of a vertical tube. The viscous lava forms volcanic domes with steep slopes, as shown in Figure 3.

What factor contributes to the gentle slopes characteristics of shield volcanoes?

The low viscosity of the magma allows the lava to travel down slope on a gentle slope, but as it cools and its viscosity increases, its thickness builds up on the lower slopes giving a somewhat steeper lower slope. Most shield volcanoes have a roughly circular or oval shape in map view.

Does the lava that forms shield volcanoes probably have a lot of silica or water in it?

does lava that forms Shield Volcanoes probably have a lot of silica or water in it? Explain your answer. Silica because the lava is very runny, and silica makes the lava runny.

Can shield volcanoes erupt?

Most shield volcano eruptions are nonexplosive (effusive), usually 0-1 on the Volcanic Explosivity Index (VEI), typically in the Hawaiian eruptive style. These eruptions produce fluid lava flows and may produce fire-fountains. High rates of eruptions help produce lava flows that travel fast and can cover large areas.