(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

As we get ready to enjoy Independence Day fireworks, Pele has been giving scientists at the Hawaiian Volcano Observatory some spectacular displays of lava activity within Halemaumau Crater.  

Views into the vent — just over a year old — on the southeast corner of Halemaumau Crater show a vigorously bubbling lava surface. This surface goes through cycles of draining and refilling up to 65 feet or more.   

Bubble bursts from this lava surface have been observed to fling spatter more than 65 feet up onto the vent walls, as well.  When rare glimpses of this activity are visible through the plume, the spatter incandesces brightly, reminiscent of a fireworks show.  

In the past, lava fountaining events on Mauna Loa and Kilauea have put on even more impressive light shows. 

But is the red light we often associate with lava really the same as that produced by fireworks?  

Lava and other very hot objects produce light by a process known as incandescence, which is the emission of light (visible electromagnetic radiation) from a hot object due to its temperature.  Most objects, like rocks, start to incandesce visibly around 450°C (840°F).

Hot objects give off infrared radiation, and, as the temperature increases, the energy emitted shifts to shorter wavelengths.  It produces, first, a red glow, then a white one, and, finally, a blue color as the peak moves out of the visible part of the light spectrum and into the ultraviolet. 

Counter-intuitively, higher temperatures are “cool” colors (white to blue), and lower temperatures, “warm” colors (yellow to red).  These colors can be seen when metal is heated to “red hot” or “white hot.” Blue incandescence is not often seen.  

This is the same light-emitting process that occurs in incandescent light bulbs, which emit only around 10 percent of their energy as visible light and the remainder as infrared radiation, making them very inefficient sources of light. 

Light from fireworks most often is from a flame, which is the visible part of combustion (burning). The color of a flame can depend on temperature and on the chemical composition of the fuel that is burning. 

In a fire, the process of combustion is not always complete and generates products like soot.  This soot becomes incandescent from the heat and gives a flame its typical orange-yellow color.  Color-producing chemicals can also be added to a flame to produce color.  For example, copper can produce blues and greens; sodium, yellow; lithium, red; and potassium, purple. 

If a flame has sufficient energy, it will excite the electrons in some of these soot-like products, which produce visible light as they release their excess energy in a process known as molecular emission.  A common example of this is the blue color in a welder’s torch.   

For both fireworks and volcanoes, the fundamental process behind some of the most spectacular events that we have witnessed is the same. They are both the expression of a system trying to let off excess energy.  In the case of fireworks, combustion of a gunpowder-like substance produces a high amount of heat and rapidly expands.

Because it is confined to a container, pressure builds until a loud explosion is produced.  Similarly, for volcanoes, excess heat within the earth builds up high pressure in the form of pressurized volcanic gas and magma until an opening is found at the surface for releasing that pressure—sometimes explosively. 

Both can put on spectacular visual and audible shows, and both can also be dangerous. They are best viewed from a distance, preferably on a picnic blanket under the stars.