Lava comes in a wide range of colors depending on its chemical composition. The color provides clues as to the lava’s temperature and mineral content. While many think lava is a glowing red or orange, it can actually take on shades of gray, brown, blue, and even green. Understanding the science behind lava’s color variations can help volcanologists predict a lava flow’s behavior.
What gives lava its colors?
The primary factor determining lava’s color is its chemical composition. The minerals that make up the lava, and their concentration, affect the wavelengths of light that are absorbed or reflected, resulting in different colors. For example, iron-rich lavas tend to look redder because iron absorbs bluer light. Lavas high in magnesium and calcium appear darker gray or black. The presence of other elements like titanium and sulfur can also tint lava’s color.
In addition to composition, lava color depends on its temperature. Hotter lavas, around 2,000°F (1,100°C), glow orange or yellow because they emit more light at red and yellow wavelengths. Cooler lavas below 1,000°F (540°C) look redder because they shift toward emitting less yellow/orange light.
What are the main lava colors?
Here are some of the most common lava colors and what they indicate about the lava’s composition and temperature:
| Color | Temperature | Composition |
|---|---|---|
| Bright red | 1,000-1,200°F (540-650°C) | High in iron and magnesium |
| Dark red | 900-1,000°F (480-540°C) | High in iron and magnesium |
| Orange/Yellow | 1,200-2,000°F (650-1,100°C) | High in sulfur and iron |
| Black | 1,200-2,000°F (650-1,100°C) | High in magnesium and calcium |
| White/Light gray | 1,800-2,000°F (980-1,100°C) | High in aluminum and silica |
The wide range of lava colors arises from differences in lava temperature and the relative proportions of elements like iron, magnesium, calcium, aluminum, silica, sulfur, sodium, and potassium. Let’s look at some examples of common lava colors in more detail.
Red lava
Red is perhaps the most iconic lava color. The familiar glowing red/orange rivers of lava oozing down Hawaiian volcanoes represent mafic lava. Mafic refers to lava containing high levels of iron (Fe) and magnesium (Mg). Iron makes up around 10-15% of mafic lava and is responsible for its red/brown color. Bright red lavas indicate cooler temperatures around 1,000-1,200°F (540-650°C). Dark red lavas are even cooler at 900-1,000°F (480-540°C).
Black lava
Black lava, also known as basaltic lava, contains abundant iron and magnesium like mafic lava. However, it also has very high levels of calcium (over 10%) which gives it a dark gray or black appearance. You’ll see this dark lava flowing in places like Hawaii, Iceland, and Italy. The high calcium content makes the lava more viscous so it can’t flow as far and cools quickly into thick rock formations. Black lava’s temperature ranges from around 1,200-2,000°F (650-1,100°C).
Brown lava
Brown lava indicates the presence of volcanic glass. When lava cools quickly, its minerals don’t have time to form crystals. The result is brown obsidian glass. Obsidian is rich in silica (SiO2), typically 70% or more. High silica gives the lava a thicker, more viscous consistency. Brown and black can be difficult to distinguish, but brown lava lacks basalt’s metallic sheen. You’ll see brown lava glass at volcanoes like Yellowstone and Mt. St. Helens.
Blue lava
While less common than red and black lavas, blue lava does occur in places like Indonesia and Ethiopia. The blue comes from extremely high temperatures of over 2,200°F (1,200°C). At these blistering temperatures, the lava emits more light in the blue part of the spectrum. Blue lava may also form when sulfur and copper minerals are present. The sulfur combines with copper to create the blue copper sulfate mineral chalcanthite. But intense heat is the more common cause of blue lava.
Green lava
Green is one of the rarest lava colors. Unlike blue and black lavas that form through heat and mineral content, green lava gets its color from secondary processes. When lava interacts with seawater, olivine crystals in the lava alter into green minerals called chlorites and serpentines. You’ll see this green lava along coastlines where lava flows into the ocean. The island of Surtsey off Iceland’s southern coast provides a great example of green lava formed from seawater alteration.
Shades of gray
Light gray or white lava indicates high levels of silica, over 68%. You’ll often see pumice or rhyolite lava look gray or white-hued. The high silica makes the lava very viscous, so gases can’t escape, forming cooled bubbles of pumice. Light gray lava may also simply result from intermediate chemical compositions, without extremes of any element. Hawaii’s Mauna Kea volcano erupts these intermediate gray lavas. Pure light gray to white lava can indicate temperatures reaching 1,800-2,000°F (980-1,100°C).
Conclusion
Lava exhibits an incredible spectrum of colors that provide insights into its composition and volcanic origins. While red is the stereotypical lava color, in actuality lava can range from brown, black, and blue to green and white. What makes lava appear a certain color comes down to its unique mineral and chemical profile, as well as how hot the lava is. Understanding the science of lava color variation helps volcanologists better analyze an eruption and predict how lava flows will behave.
