Taal Volcano in the Philippines suddenly erupted, so how is lightning formed?

On January 12, the Taal Volcano in the Philippines suddenly erupted. The volcanic ash shot into the sky 10-15 kilometers high and even spread to Quezon City 72 kilometers away. It also triggered earthquakes and tsunamis. We marvel at the spectacular sight and destructive power of volcanic eruptions. I believe everyone has seen the magical lightning phenomenon from photos and videos, which is much more spectacular than the atmospheric discharges we see. Now let’s talk about the physics of volcanic lightning. How does it happen?

One of the most common natural phenomena in our atmosphere is lightning. In each lightning strike, approximately 100,000,000,000,000,000,000 electrons are exchanged between clouds and the Earth's surface. First, let’s talk about how atmospheric discharge occurs? Every atom in the universe, including those in the atmosphere, is composed of a positively charged nucleus and a large number of negatively charged electrons. Although we usually think of atoms as neutral, with the number of electrons equal to the number of protons in the nucleus, there are special cases.

Because some atoms are happy to be ionized, either gaining an electron or losing one (or two, or three) electrons. Just like the sodium atom in the picture above is happy to kick out the outermost electron and become a positively charged sodium ion, while the chlorine atom always feels that it is missing one electron and hopes to become a chlorine ion by gaining an electron. Now, if we separate these charged particles from each other, we create charge separation, which creates a voltage. When the voltage (also called the potential difference) between two areas becomes large enough, even if there is only air between them, the air will spontaneously conduct electricity, a rapid charge exchange occurs, and we see lightning! Lightning basically occurs at high altitudes, usually between clouds or between clouds and the ground. However, volcanic eruptions often produce lightning too! The picture below shows lightning during the eruption of Eyjafjallajökull in Iceland.

Here are some amazing photos of volcanic lightning that were actually taken. The picture below is a photo of the eruption of the Eyjafjallajokull volcano in Iceland, taken by a helicopter!

The pictures above and below show that the lightning during a volcanic eruption is no less than any atmospheric discharge phenomenon.

Historically, it has been very difficult to capture lightning at close range during volcanic activity, such as when Chile's Chaitin volcano erupted in 2008 for the first time in 9,000 years. erupt.

Sakurajima, Japan, is a very active volcano in modern history, erupting almost continuously since 1955. A volcano observatory was established in 1960 to continuously monitor its activity, and volcanic lightning has been observed on several occasions, including this eruption in 1988.

In fact, volcanic lightning was photographed as early as 1944 when Mount Vesuvius erupted! Pictured below:

So how does volcanic lightning occur? To be honest, scientists believe that volcanic lightning works on the same principle as normal thunderstorm lightning, but some details are not 100% certain yet, and this is still an area of ​​ongoing research. But there is a general idea of ​​why things like this happen when volcanoes erupt.

(Step 1) In most cases, atoms are neutral at first, but due to the existence of a large amount of free energy, these energies will knock off some electrons loosely attached to the atoms. That is to say, some atoms that originally want to lose electrons are ionized, and at the same time, those atoms that are eager to obtain these newly released electrons can quickly capture these free electrons. (Step 2).

The above two steps are absolutely fine: because this is a volcano!

When the temperature is around 1500k, there must be enough energy to kick electrons out of some of the loosest atoms, and then these electrons are easily absorbed by other atoms, creating a large number of positive and negative ions.

Now, the key step is, and it is currently a controversial step. With positive and negative particles, it is necessary to separate the positive and negative charges (step 3). And enough particles must be separated to generate enough potential difference within a certain distance to cause a discharge phenomenon! (Step 4). If we could separate charges, we could theoretically create volcanic lightning. So how do we differentiate between these charges? Now a large number of ionized atoms, including positive and negative ions, are in a high-temperature, chaotic environment. And these atoms are ejected from the depths of the earth, which contain many rich elements.

These elements have different masses from each other, as well as different radii! When they are ejected by volcanoes, the temperature gradually decreases over time. This is very important for the speed of the atom/ion in question.

Generally speaking, when atoms and ions are ejected, they move quickly at first, but slow down as they cool down over time. There are two very important factors here that make it easy for us to separate positive charges and negative charges. First of all, the masses of these ions are very different! The heavier an element's atomic weight, the slower it moves, even at the same temperature as the lighter element! This also means that heavier ions have greater inertia, making it more difficult to change their momentum. So these slow-moving heavy ions move very differently than the fast-moving light ions.

This is true at any temperature!

The second very important factor: What separates these positive and negative ion types from each other? There is a huge difference in size and cross-section between positive and negative ions.

Generally speaking, the cross-section of negative ions is large, while the cross-section of positive ions is small! Why is this? Because if you put more electrons on an atom, they will repel each other; if the atom is neutral, the size of the atom will increase and the nucleus (which has fewer protons than the number of electrons in the ion) cannot hold tightly together. Grab the electron.

On the other hand, in order to become a positive ion, the atom kicks the electrons out of the atom, and the nucleus (which has more protons in the ion) is able to hold on to the electrons much tighter than before! This means that negative ions have a larger cross-section than positive ions, so they interact very differently than positive ions!