In this Expedition, you’ll get a close-up look at Tolbachik, one of those active volcanoes, and learn about why this region has so many volcanoes.
Tolbachik Volcano
Tolbachik is a volcanic complex in central Kamchatka that is made up of two different kinds of volcanoes. Shield volcanoes build gradually. They are made of many layers of lava, the melted rock that pours out when a volcano erupts.
Over time, the lava layers create mountains that are shaped like domes, with gently sloping sides. Stratovolcanoes build relatively quickly, with much more powerful explosions than shield volcanoes. Stratovolcanoes are shaped like cones.
Plosky Tolbachik
Tolbachik has two sections, which are examples of two different kinds of volcanic activity. Plosky (Flat) Tolbachik is a shield volcano. Shield volcanoes build gradually. They are made of many layers of lava, the melted rock that pours out when a volcano erupts.
Over time, the lava layers create mountains that are shaped like domes, with gently sloping sides.
Ostry Tolbachik
The Ostry (Sharp) Tolbachik section is a stratovolcano. A stratovolcano builds relatively quickly, with much more powerful explosions than a shield volcano. Stratovolcanoes are shaped like cones.
Udina Bolshaya
Udina Bolshaya, which lies about 12 kilometers from Tolbachik, is another stratovolcano. We know it’s a stratovolcano from its conical shape.
Elements in an Eruption
Earth’s crust, or outer layer, is hard rock. But under the crust there are layers of softer rock and magma, rock so hot that it has melted. Volcanoes happen when heat pressure causes magma to rise up through the cracks in the crust and flow out onto Earth’s surface.
This picture shows some of the physical elements that are part of volcanic eruptions.
Gas and Steam
Usually the first signs that a volcano is erupting are ground tremors and earthquakes. Next come feather-shaped clouds that rise out of vents, or openings, in the underlying rock.
Volcanic clouds contain poisonous gases, such as carbon monoxide and sulfur dioxide, as well as carbon dioxide and steam. The steam comes from underground water that has been heated by the rising magma.
Gases from active volcanoes can rise high into the atmosphere and affect air quality around the globe.
Magma (Lava)
Magma that has emerged from under Earth’s surface is called lava. This melted rock is extremely hot. If the volcano explodes with enough power, the lava shoots high into the air.
In shield volcanoes, such as Tolbachik, lava flows more gently, over the sides of the vent and across the ground. On the slopes below the volcano’s vent, we can see previous flows of lava that are now covered with snow.
Cinders and Ash
The volcano’s intense heat reduces rocks and soil to ashes. The ash and small particles of hot rocks, or cinders, build up around the volcano’s vents. As eruptions continue, the ash and cinders build into conical shapes.
In the most powerful eruptions, ash and cinders get blasted high into the air and rain down on the surrounding land. Ash deposits can cover hundreds of square miles.
Cinder Cones
Ostry Tolbachik, Udina Bolshaya, and other stratovolcanoes have conical shapes because of the immense quantities of cinders and ash that they eject. The cinders and ash flow down in all directions, creating smooth, even sides.
Lava
Magma from Earth’s core becomes lava after it reaches Earth’s surface. The word lava describes not only the melted form of the rock but also the solid rock that forms when lava cools. Dome-shaped shield volcanoes such as Plotsky Tolbachik are formed by many layers of solidified lava.
Fissures and Vents
As heat pressure builds inside a volcano, more cracks appear in the rock. It is quite common for an active volcano to erupt in several different spots. The main vent of this eruption appears near the top of the hill.
But we can also see a smaller narrow fissure that also starts at the top of the hill and a smaller vent that is opening farther down the slope.
Lava Flows
After a volcano erupts, streams of lava move down the slopes, consuming everything in their paths. Lava is very thick and usually flows relatively slowly, allowing enough warning time to prevent loss of human life.
In highly explosive volcanoes, lava flows can combine with hot gases to form pyroclastic flows, which move very quickly—as much as 100 kilometers and more per hour.
Mud Flows (Lahars)
Because this volcano is erupting on a snow-covered slope, some of the snow is melting. Like lava flows, mud flows (also called lahars) can flow down through river valleys, covering and ruining the surrounding land. Lahars are especially destructive when volcanic activity occurs in heavily populated areas.
Reshaping the Land
In this panorama we can see one of the long-term effects of volcanic activity. As lava flows, cools, and hardens, it reshapes the land under and around it. Tongues of lava form pathways to the seashore and beyond.
Lava flows can build new peninsulas and shelves out into the ocean. Ash from the volcano, sand washed ashore by ocean waves, and mud washed down from mountain slopes then build up on top of the hardened lava, creating new soil. Volcanic soils are among the most fertile on Earth, especially in tropical areas.
Why Tolbachik Erupts
The Tolbachik volcano is located on the Kamchatka Peninsula, one of the most active volcanic zones on Earth. Hundreds of volcanic peaks provide evidence of the peninsula’s long and explosive geological history. The scientific theory that explains these volcanoes is called plate tectonics.
Pacific Plate
Earth’s crust has many long cracks, or faults. The land areas between the cracks are called plates. One of Earth’s largest tectonic plates, the Pacific Plate, makes up the sea floor under the Pacific Ocean.
Down the middle of the Pacific Plate there is a chain of underwater volcanoes. As these volcanoes erupt, they build the land, and the Pacific Plate expands.
The western side of the plate expands toward Asia (including the Kamchatka Peninsula). The eastern side of the plate expands toward North America (including Alaska).
Eurasian Plate
Another very large tectonic plate, the Eurasian Plate, makes up the continents of Europe and Asia. The Kamchatka Peninsula is on the northeastern edge of the Eurasian Plate.
Just north of Kamchatka, the Eurasian Plate adjoins the North American plate. The Kamchatka Peninsula is volcanically active because it is located near where three tectonic plates join.
Subduction
The Pacific Plate, under the Pacific Ocean, is gradually expanding in the direction of the Kamchatka Peninsula. When the edge of the Pacific Plate reaches the edge of the Eurasian Plate, the Pacific Plate sinks under the landmass of Asia.
This process, which is called subduction, gradually lifts the Eurasian Plate, causing earthquakes and triggering volcanic activity.
“Ring of Fire”
The “Ring of Fire” is the imaginative label used by scientists to describe the chain of active volcanoes that circle the Pacific Ocean. The volcanoes occur along the faults that separate Earth’s tectonic plates.
The Pacific Plate, which lies under the Pacific Ocean, pushes against the tectonic plates that surround it: the Eurasian, Philippine, Indo-Australian, Antarctica, Nazca, Cocos, and North American Plates.
There are volcanoes along all the fault lines, the edges where the plates meet. The entire Pacific Coast, on the continents of Asia, Australia, Antarctica, South America, and North America, is lined with volcanoes. Hundreds of these volcanoes are active.
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