# Why does New Zealand and cold countries have volcanoes?

I understand that volcanoes are caused by the heat that causes high intense pressure below the Earth's surface. This intense pressure gets released and causes magna which becomes hot lava to flow out from inside the Earth.

Why does it happen in New Zealand or any cold countries? There is no way that the Earth will be over-heated there.

• Think about why Jupiter's moon Io is the most volcanically active body in the solar system, when its surface temperature is about -130°C (-200°F). – jamesqf Jul 6 '15 at 17:37
• Where I live, hot days don't come close to producing lava. Maybe that's just Canada... – Peter Cordes Jul 7 '15 at 4:13
• Peter Cordes: Yes, also note the lack of volcanos in the Sahara & Australian Outback. – jamesqf Jul 7 '15 at 17:25

Surface temperatures on Earth are a consequence of solar heating and radiative cooling - in other words, the heat energy which drives climate comes from sunlight falling on the Earth "now".

On the other hand, the heat energy driving volcanism is left over from the formation of the Earth (4.5 billion years ago), stored deep inside the planet, with some additional heat generated from the radioactive decay of elements contained in the rocks.

Deep within the Earth, the temperature is on the order of 5000-7000 K. It's obviously much cooler at the surface. The high temperatures cause the rock and metal of which the Earth is composed to melt. The temperature gradient results in a slight density gradient, which drives convection (flow of hot material up to the surface). When that hot material breaks through the surface, you have a volcano.

Consider that the hottest places on Earth (in terms of climate) don't have surface temperatures anywhere close to what it takes to melt rock (maybe 50 °C compared to 1000s of °C). Heat can only move from where the temperature is higher to where it is lower. Less heat falls on the planet from the Sun than the Earth radiates away into space; that difference is heat finding its way up to the surface from within. So, the heat driving volcanoes cannot possibly be coming from sunlight striking the Earth; it can only come from heat stored inside the planet from long ago. Consider also that the difference in temperature between the hottest places on the Earth and the coldest (in terms of climate) differ by little more than 100 °C. That's a tiny fraction of the temperature difference between molten magma and even the hottest desert. Bottom line: climate has no effect on volcanic activity.

Since the Earth is losing more heat to space than is falling on it from the Sun, and that heat is coming up from below, the core is gradually cooling. But there is so much heat inside the Earth and the rate is so slow that our Sun will die before Earth's core cools enough to solidify.

The Earth's surface temperature is largely determined by the amount of energy it receives from the Sun and how much of that energy is reflected back into the cosmos. Weather system circulate that energy in the atmosphere.

Heat within the Earth is the result of two main processes, residual heat from planetary accretion and heat from radioactive decay. The main decay elements are potassium-40, uranium-238, uranium-235, and thorium-232 . The temperature of the Earth increases with depth. For most of the Earth, the geothermal gradient (the rate at which temperature increases) particularly in the crust, is $25$ $^oC$ per km.

In subduction zones, where one tectonic plate goes under another tectonic plate (two plates converge), localized heating occurs due to friction between the plates. Subduction zones are locations with high rates of volcanism, earthquakes and mountain building; as occurs in New Zealand.

Geological hotspots are volcanic locations where it is thought the mantle is anomalously hot compared to the surrounding mantle. They occur on or near plate boundaries, or far away from them. Hawaii is a hotspot away from a plate boundary and in the middle of the largest ocean on Earth. Yellowstone is a hotspot on land, near the plate boundaries along the west coast of North America. Iceland is thought to be a hot spot on a diverging plate boundary in the middle of the Atlantic Arctic region.

The Volcanism of Earth has nothing to do with the surface temperature of the planet, it's all about geological processes where molten rock is forced to the surface of the planet under pressure.

Additionally, volcanism isn't confined to the Earth. Mars was once volcanic, Venus still is, as is the Jovian moon Io, the Saturnine moon Enceladus and the Neptunian moon Triton. These are examples of volcanism within our solar system. Except for Venus, all the other locations of volcanism in the solar system have very cold surface temperatures.

On Io,

Magma erupts onto the surface from vents on the floor of paterae or on the plains from fissures, producing inflated, compound lava flows similar to those seen at Kilauea in Hawaii

Whereas, Enceladus and Triton experience cryovolcanism, where ice and water are ejected under pressure.

• Good and correct answer! Maybe it could be further clarified that vulcanism is caused by a combination of temperature, pressure and composition, not just temperature as it might seems that OP assumed in the question. – Tactopoda Jul 7 '15 at 14:09

The countries you refer to are only cold at the surface of Earth. Once you dig down a short ways (I'm not a geologist, so I hope they forgive me if I ballpark a number), say a hundred meters or so, the temperatures become fairly consistent all across the globe. Furthermore, the buildup of pressure under the surface has no relevance to the surface temperature above. Tectonic activity, hot spots, and tidal friction (not so much that last one for Earth) are what cause the heat and pressure to form volcanoes.

Places that lie near subduction zones - which are converging fault lines where the sea floor is pushed under another plate - are prone to volcanism because the sinking plate puts increased pressure and some friction on the (in New Zealand's case) continental plate. You end up with a compactified continental plate (mountains) and large pressure/heat buildup (volcanoes). That is the case with New Zealand. Other cold areas, like Iceland, can be formed directly from diverging faults - regions where tectonic plates are separating and allowing the mantle to flow to the surface. This creates volcanism that manifests more as things like hot springs and lava tubes rather than as big, mountainous, andesite volcanoes. Hot spots are a different entity entirely. A hot spot is not necessarily related to tectonic activity, it is simply a region of the mantle that is over-heated and so causes volcanism at the surface above it. This spot does not move with the rest of a tectonic plate, which is why the Hawaiian island chain has moved progressively; the plate moved the islands off the hot spot, so there's now a string of dead volcanic islands that are arranged by age. Iceland also has some hotspot activity on top of being on a diverging fault. Regardless of how cold it is, in the mantle below Iceland the temperatures are abnormally high. This, again, is possible because the surface temperatures do not penetrate far enough down to affect the mantle temperatures in any significant way.

Regardless the cause of the volcanism, it has absolutely nothing to do with surface temperature. That only impacts the immediate surface of Earth and not in any way that would either prevent or stimulate the buildup of subsurface pressure and heat.

• This post is one giant [citation needed]. I only hope a real geologist comes along and doesn't want to lynch me for any of this – Jims Bond Jul 6 '15 at 13:55
• In Iceland, the proximity of the mantle to the surface not only results in volcanism, it supplies the country with abundant hydrothermal energy. – Mike Dunlavey Jul 6 '15 at 14:16
• @MikeDunlavey I think you mean geothermal energy. But yes, that's the benefit of being the most volcanically active country on Earth – Jims Bond Jul 6 '15 at 14:25
• Almost perfect - except the part about friction and pressure. At high temperatures and pressures, that is deep in the Earth, rocks start flowing like chocolate, even though they're not melted yet. Think hot chocolate. Therefore, friction plays a very minor role in the actual heating up of the rocks. Furthermore, most of the volcanic activity on the planet is actually caused by a pressure drop, not increase. – Gimelist Jul 7 '15 at 3:22
• I believe the presence of water at subduction zones is important - it reduces the melting point of rocks and thus helps create magma. I once asked a geologist why there were few or no volcanoes on the Tibetan plateau, which is above a subduction zone, and she mentioned that there is little water in the material being subducted there, as compared to the ocean sediments being subducted around the Pacific ring of fire. – sdenham Jul 7 '15 at 15:35

As others have pointed out, the surface temperature does not effect volcanic activity and this is related to the movement of two (or more) plates relative to each other.

The border of the Pacific and Australian plates passes through the south island of NZ, which leads to earthquakes and volcanoes. The border around the Pacific Plate is known as the ring of fire, and almost all regions along it are prone to Earthquakes and Volcanoes.

This is why Southern parts of Australia, despite being at the same latitude as much of New Zealand and in the same general area of the world, are not prone to earthquakes or volcanoes, they are at the centre of a plate instead of the edge.

• Mainland Australia has no active volcanoes (the last eruption was several thousand years ago), but we do get earthquakes. Usually these earthquakes are mild enough to cause shaking but no damage, although there have been a few much more powerful quakes such as the 1989 Newcastle earthquake. – CJ Dennis Aug 11 '18 at 23:29

This is a pure statistical response but the answer is clear and makes sense when you think about the fact that practically all of New Zealand lies on the Ring of Fire which houses 75% of the world's volcanos.

The ring of fire runs across the entire globe and is independent of the climate.

• "entire globe". Don't you mean the "entire Pacific Ocean"? – Peter Mortensen Jul 10 '15 at 18:14
• I'm pleased to say that the plate edge leaves well down the North Island giving we Aucklanders a buffer zone. Instead in Auckland we have an off-plate-edge hotspot that has so far given us 50+ small volcanos and, I'm told, more again very small ones. The next is rather overdue. I'm outside the hotspot zone (so far) but have a ringside seat for the next event if I'm still around when it happens - about 3 miles from the extreme Westerly edge (rather close) although the last millenia or so most volcanos have been 10-20 miles from here. – Russell McMahon Aug 31 '16 at 13:18