Analyze This: Can you outrun these geological disasters? | Science News for Students

Analyze This: Can you outrun these geological disasters?

Yes — and well probably not
Sep 5, 2018 — 6:30 am EST
a short clip of lava oozing down a road and glowing red and orange at night

This May 2018 video of lava flowing down a road was captured during the eruption of Kilauea on the island of Hawaii.


Red hot lava races down the slopes of a volcano, along with billowing clouds of ash, toxic fumes and huge rocks. People, dinosaurs and vehicles are desperately speeding away, staying just ahead of the molten rock and ominous clouds. Because, well, life finds a way (it has to). If this sounds familiar, that’s because this is a scene from the recent summer movie blockbuster, Jurassic Kingdom
Aside from the dinosaurs, though, just how realistic is this scenario? Could people actually outrun the dual dangers of lava and a pyroclastic flow? What about other geological disasters, such as landslides or avalanches? The movies, it turns out, aren’t always totally fiction. 

Lava flow

Lava is the molten rock that comes out of a volcano. How quickly lava flows depends on factors such as its chemical composition, its temperature, and its gas and fluid content. Researchers measure its speed with the same radar gun that police use to catch speeding cars. And, they find, hotter lavas can move pretty swiftly when they contain plenty of gas, such as water vapor, carbon dioxide and sulfur dioxide.

There are two main types of lava: basaltic (Bah-SAAL-tik) and andesite (AN-deh-syte). Basaltic lava is generally more fluid and free-flowing. It tends to produce low-profile shield volcanoes, such as Kilauea in Hawaii. In contrast, andesite lava contains more silica than basaltic lava. That makes it thicker, creating slower lava flows and taller volcanoes, such as those found in the Andes.

Occasionally, lava can travel briskly, such as when it’s in a lava channel, lava river or lava tube. These are pathways that direct and insulate the lava flow, allowing it to move much more swiftly. These pathways form when friction slows the outer edges of a lava flow. As those edges cool they also crust over and harden. This allows them to channel the lava flow, like the edges of a creek or river channels water.

The rest of the time, though, a person should be able to escape a lava flow easily.

A glowing river of lava races from fissure 8 on Kilauea’s lower east rift zone all the way to the ocean.
USGS/Science News/YouTube

Pyroclastic flow

This is the movie industry’s classic type of volcanic eruption. Here, a giant cloud of ash, toxic fumes and large chunks of solidified lava travel downhill in the company of searing hot gases — some as hot as 1,000° Celsius (1,830° Fahrenheit). Most people unfortunate enough to be near such a fast-moving event won’t escape it. The Volcán de Fuego in Guatemala, for instance, released a lethal pyroclastic flow during an eruption this summer. It killed more than 100 people.

a photo of pyroclastic flow from Mt. St. Helen's in 1980
Here, a pyroclastic flow rushes down Mt. St. Helen’s on August 7, 1980. This volcano is a landmark of Washington state, Under the giant cloud of ash and toxic gas moves a wave of hot and fast moving debris — and lava rocks.
P.W. Lipman/USGS


Sometimes the rocks and soil on a slope give in to gravity. The resulting downhill flow is known as a landslide. Heavy rains and earthquakes are among events that can trigger a landslide. Human alterations to the environment can aggravate the risk that this will happen. Examples of such changes are stripping plants from hillsides or cutting into hillsides to build roads. Now this land may erode and give way during rains.

“Landslide is a generic term for a kind of land flow movement,” explains Dave Petley. A geographer and earth scientist, he works at the University of Sheffield in England. What a landslide looks like and how fast it moves depends on many things. Most land flows move just a few centimeters (inches) a year. Others can move very fast and with little warning.

an aerial image showing the aftermath of a landslide in the distance
A helicopter flies over the site of a landslide on the Phillippine island of Letye in February 2006.
Petty Officer 1st Class Michael D. Kennedy/US Department of Defense/Wikimedia Commons

Mudslides are a specific type of landslide where debris and dirt mix in with water. Mudslides tend to be slower than other land flows. They also have the potential to be very powerful and to pick up debris as they travel.


Sometimes water mixes with volcanic sediment and debris to create a powerful, fast-moving river that gushes down a volcanic slope. Its structure tends to resemble flowing concrete. Lahars can be triggered by severe rainfall in a volcanic area that has lots of loose sediment. They also can develop when a volcanic eruption melts glacial snow on the sides of a volcano.

an aerial photo of where the Columbian town of Armero used to stand, covered in mud and ash

an aerial photo of the town of Armero in Colombia showing the only buildings left standing after a lahar.

In 1985, the Nevado del Ruiz volcano in Colombia erupted. Pyroclastic flows burst from the volcano. These melted glaciers on the mountain’s slopes. The several lahars that this created poured down the mountain at high speed. Nighttime lahars swept through the town of Amero with no warning, leaving 20,000 dead.


a photo of a powder snow avalanche in the Himalays pouring down a steep slope
A powder snow avalanche in the Himalayas, near Mount Everest, in 2006.
Chagai/Wikimedia Commons

Large amounts of snow sometimes break off a mountain or hill to tumble downward — often without warning. These avalanches can be triggered when something disturbs a snowpack, such as a skier or an earthquake. The most dangerous avalanches, known as dry slab avalanches, occur when a very cold and very dry snowpack destabilizes. The unstable snow now rushes downhill, fanning out and picking up more snow along the way, which further feeds the avalanche.


Disasterslowest speed (kph)*fastest speed (kph)*
lava (andesite)02
lava (basalt)<110
avalanche (dry slab)30130
pyroclastic flow80.5724

*All speeds are presented in kilometers per hour (kph) and are estimates that can vary depending on situation and topography.

Data Dive: 

  1. Use the data to create a graph or chart. Be sure to use appropriate labels.
  2. What is the most surprising thing about these data?
  3. Convert the table from kilometers per hour to miles per hour.
  4. Could you escape a lava flow on foot? What about in a car? (Hint: Take into account where these events might occur.)
  5. Which three disasters would you have the most chance of escaping on foot?
  6. Which disasters would you have the most chance of escaping in a car?

Analyze This! explores science through data, graphs, visualizations and more. Have a comment or a suggestion for a future post? Send an email to

Power Words

(more about Power Words)

andesite     A gray to black type of volcanic rock with between with about half the density of silica. Andesite lava commonly erupts from volcanoes in thick flows. They may travel some kilometers (miles) before hardening. Andesite magma can also trigger explosive eruptions characterized by pyroclastic flows.

ash     (in geology) Small, lightweight fragments of rock and glass spewed by volcanic eruptions.

basalt     (adj. basaltic) A type of black volcanic rock that tends to be very dense (unless volcanic eruptions seeded it with lots of air pockets). 

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

cloud     A plume of molecules or particles, such as water droplets, that move under the action of an outside force, such as wind, radiation or water currents.

concrete     (in construction) A simple, two-part building material. One part is made of sand or ground-up bits of rock. The other is made of cement, which hardens and helps bind the grains of material together.

debris     Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.

dynamic     An adjective that signifies something is active, changing or moving. (noun) The change or range of variability seen or measured within something.

eruption     (in geoscience) The sudden bursting or spraying of hot material from deep inside a planet or moon and out through its surface. Volcanic eruptions on Earth usually send hot lava, hot gases or ash into the air and across surrounding land.

geography     The study of Earth’s features and how the living and nonliving parts of the planet affect one another. Scientists who work in this field are known as geographers.

geological     Adjective to describe things related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.

Jurassic     Lasting from about 200 million to 145.5 million years ago, it’s the middle period of the Mesozoic Era. This was a time when dinosaurs were the dominant form of life on land.

lahar     A thick flow of mud, ash, soil and rocks. It can develop when rains mix with the materials being spewed during a volcanic eruption. This viscous mix, can have the consistency of wet, newly mixed concrete. As it slides down a volcano’s slopes, it can destroy nearly everything in its path.

lava     Molten rock that comes up from the mantle, through Earth’s crust, and out of a volcano.

magma     The molten rock that resides under Earth’s crust. When it erupts from a volcano, this material is referred to as lava.

pyroclastic flow     Hot clouds of ash and rock that sweep down a volcano’s slopes during an eruption. These flows can move at hurricane speeds.

sediment     Material (such as stones and sand) deposited by water, wind or glaciers.

silica     A mineral, also known as silicon dioxide, containing silicon and oxygen atoms. It is a basic building block of much of the rocky material on Earth and of some construction materials, including glass.    

snowpack      A mass of slow-melting snow that collects throughout the winter at high altitudes. It eventually becomes compressed by its immense weight and hardens.

topography     (adj. topographic) The mapped shape and size of features of some landscape, typically the surface of Earth or a moon — but even, potentially, the nanoscale highs and lows of structures atop some computer chip.

toxic     Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

viscosity     The measure of a fluid’s resistance to stress. Viscosity corresponds to the idea of how “thick” a liquid is. Honey is very viscous, for instance, while water has relatively low viscosity.

volcano     A place on Earth’s crust that opens, allowing magma and gases to spew out from underground reservoirs of molten material. The magma rises through a system of pipes or channels, sometimes spending time in chambers where it bubbles with gas and undergoes chemical transformations. This plumbing system can become more complex over time. This can result in a change, over time, to the chemical composition of the lava as well. The surface around a volcano’s opening can grow into a mound or cone shape as successive eruptions send more lava onto the surface, where it cools into hard rock.

wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

Further Reading

Safety resources: Avalanche What to do if you get caught in an avalanche Volcanoes, Be Prepared for a Landslide, May 2018
USGS, Landslide Preparedness


Website: USGS Volcano Hazards Program, Lava Flows
Website: USGS Volcano Hazards Program, Pyroclastic Flows
Website: USGS, The landslide handbook—A guide to understanding landslides
Website: Michigan Tech Department of Geological and Mining Engineering and Sciences, Lahars
Website:, Avalanche