<p>Here are some general considerations on the topic.</p>
<p>1/ Be careful when using the term &quot;hazardous&quot; or &quot;hazard&quot;. In the field of natural disasters, like volcanic eruptions, hazard is used to describe a physical phenomenon that could be dangerous, or not, depending on the context. A lahar is a hazard, a pyroclastic flow is a hazard. Now that doesn't mean they present a <em>risk</em>, which is a whole different concept. Risk is usually defined as:</p>
<p>Risk = Hazard <span class="math-container">$\times$</span> Vulnerability</p>
<p>Which means that if the vulnerability is null, then the risk as well, even if the hazard is great. In volcanology, a good example of this is the <a href="https://en.wikipedia.org/wiki/Novarupta" rel="noreferrer">Novarupta</a> 1912 eruption: it was the largest explosive eruption of the 20th century (beating Pinatubo 1991, and dwarfing St Helens 1980), yet it occurred in a remote, unpopulated area, hence had no effects on human communities. The hazard was great, but there was zero vulnerability, thus zero risk.</p>
<p>2/ Be careful when comparing hazards between them. You seem to imply that a volcano doing &quot;only&quot; lahars would be less dangerous than a volcano that would do an explosive eruption, but it all depends on the local context (i.e., the exposure of local populations to those different kinds of hazards). Lahars can be quite deadly, as recently demonstrated at Marapi (Sumatra, Indonesia), with 67 victims on May 11, 2024 (not to mention the <a href="https://en.wikipedia.org/wiki/Armero_tragedy" rel="noreferrer">Armero tragedy</a>). In fact, lahars rank as the 4th deadliest volcanic hazards according to <a href="https://doi.org/10.1016/j.jvolgeores.2005.04.017" rel="noreferrer">Witham 2005</a> (you can see the table in <a href="https://earthscience.stackexchange.com/a/24400/18081">my answer</a> to &quot;Can people on the side of a volcano survive the eruption?&quot;). It is true that pyroclastic flows rank 2nd.</p>
<p>I don't know the specifics of those two particular volcanoes, but in summary, keep in mind that it is not only a matter of volcanic hazards: the vulnerability is an important factor to consider. If there is a settlement in a valley that could serve as a lahar corridor during an eruption of Mount Rainier, then it could be more devastating that an eruption of Mount Hood. If Mount Hood collapses like St Helens did, then it depends on where human communities are. If you look at the <a href="https://www.columbian.com/news/2010/may/18/interactive-map-mount-st-helens-eruption-victims/" rel="noreferrer">map of St Helens victims</a>, they were all North from the volcano; the eruption did not affect the southern side.</p>

CC BY-SA 4.0
2024-09-08T12:19:28.780Z
2024-09-08T12:19:28.780Z
Jean-Marie Prival
<p>All the <a href="https://en.wikipedia.org/wiki/Cascade_Range" rel="noreferrer">Cascades</a> volcanoes are <a href="https://en.wikipedia.org/wiki/Andesite" rel="noreferrer">andesite</a> composite cone stratovolcanoes, which means that, among other things, they have highly variable eruptive chemistry and behaviour.</p>
<p>Saint Helens has the most recent history of violent eruption but all four major peaks have a explosive history. The massive size of St Helens 1980 wasn't because of the material erupted, i.e. not because St Helens is a particularly explosive volcano, but because of the <a href="https://en.wikipedia.org/wiki/1980_eruption_of_Mount_St._Helens#Landslide_and_climactic_phase" rel="noreferrer">flank collapse</a> that occurred when the mountain changed shape due to lava migration.</p>
<p>Andesite volcanoes are extremely unpredictable for example the last three eruptions from <a href="https://en.wikipedia.org/wiki/Mount_Tongariro" rel="noreferrer">Mount Tongariro</a> were a small ash eruption in 2012, a <a href="https://en.wikipedia.org/wiki/Basalt" rel="noreferrer">basaltic</a> low silica eruption that I frustratingly can't find the date for right now and a previous quite large ash eruption in the 1890s.</p>
<p>Rainer has a similar history of varying eruptions but with an even more violent <a href="https://en.wikipedia.org/wiki/Rhyolite" rel="noreferrer">rhyolite</a> phase though it has been far less active in recent history, with the last cone building eruptions ending ~1000 years ago and the last, small, eruption c.1450AD. The reason that <a href="https://en.wikipedia.org/wiki/Lahar" rel="noreferrer">lahars</a> are a possible outcome if Rainer erupts is that it has a history of explosive eruptions that have laid down thick ash layers on it's slopes. But Rainer may well be extinct, no longer being feed magma from the <a href="https://en.wikipedia.org/wiki/Subduction" rel="noreferrer">subduction</a> of the <a href="https://en.wikipedia.org/wiki/Pacific_Plate" rel="noreferrer">Pacific Plate</a> in which case no eruptive activity should be expected. If however Rainer ever does erupt again it's now highly eroded cone will probably be prone to slope collapse, Mount St Helens style, potentially resulting in a massively violent blast.</p>
<p>Mount Hood has never been quite as high in silica as Rainer, and thus has a less violent ancient history but as an andesite it is equally unpredictable and is also highly eroded making the cone fragile and prone to collapse if it erupts again.</p>
<p>In short none of the big four Cascade Volcanoes are anything I'd want in my backyard and of the two in the question neither is particularly safer than the other. You can't make any assumptions or estimates of future activity based on the history of andesite volcanoes because their chemistry is too prone to sudden change.</p>

CC BY-SA 4.0
2024-09-09T02:40:56.690Z
If Mount Rainier were extinct, would there still be seismic activity directly underneath it(Earthquake swarms)? I live in the PNW so Mt Rainier is very much in my backyard...I just hope it doesn't blow up anytime soon as it will be sad to lose such a majestic mountain.
Mr X
CC BY-SA 4.0
2024-09-09T02:46:02.413Z
@MrX Maybe, it depends on the type and depth of the earthquakes in question and that depends on what *exactly* the plate boundary is doing at depth. What you wouldn't see is [harmonic tremor](https://en.wikipedia.org/wiki/Harmonic_tremor), that is specific to the movement of magma.
Ash
CC BY-SA 4.0
2024-09-10T13:08:29.593Z
Purely out of curiosity, that would mean that Mount Mazama was also an andesite volcano before its collapse?
Idran
CC BY-SA 4.0
2024-09-11T00:15:25.767Z
@Idran Given it's description and the tectonic setting it certainly appears to have been, the eruption that led to it's collapse was very high silica, possibly a rhyolite chemistry but it's not unusual for an andesite to have a single episode with extremely high silica, or an episode with very little, that's what makes them *so* dangerously unpredictable.
Ash
CC BY-SA 4.0
2024-09-11T22:20:53.337Z
One more question : I looked at data from the USGS about earthquake swarms on Mt Rainier and Mt Hood respectively. Mt Rainier shows a linear increase in seismic activity over the past 50 years whereas with Mt Hood there is an exponential increase in seismic activity. Does that mean anything? It doesn't say whether the quakes are harmonic tremors or not though.
Mr X
CC BY-SA 4.0
2024-09-12T02:13:26.103Z
@MrX 50 years is a lot for us, but it's the blink of an eye in [geological time](https://en.wikipedia.org/wiki/Geologic_time_scale), far less than the error bars on most dating techniques. We may realise that it was a significant thing in hindsight one day but for now we can't really point at it and say "that means this" as with many problems in geology we just don't have enough data over time to assess such slow moving processes.
Ash
CC BY-SA 4.0
2024-09-08T05:39:05.930Z
2024-09-08T05:51:30.417Z
2024-09-08T05:51:30.417Z
Ash
<p>It is my understanding that Mount Rainier, despite its looming size, is a fairly quiet volcano. An eruption would mean lahars and mud flows, but would not be an explosive eruption like Mt Saint Helens in 1980.</p>
<p>Whereas Mount Hood is an explosive volcano and an eruption would be as violent if not even more violent and destructive than Mt Saint Helens.</p>
<p>Is this correct? The 19th century Mt Rainier eruptions did little damage to the mountain(if any at all). Is there a reason to suspect a more vigorous eruption next time?</p>

CC BY-SA 4.0
2024-09-10T00:32:00.467Z
You seem to be of the opinion that a lahar is not a major hazard.  Consider the fact that the city of Tacoma is built on top of debris from a 5000-year-old lahar.
Mark
<volcanology><volcanic-eruption>
Which volcano is more hazardous? Mount Rainier or Mount Hood?
Mr X
# Which volcano is more hazardous? Mount Rainier or Mount Hood?

(Asked by: username_0 on 2024-09-08)

It is my understanding that Mount Rainier, despite its looming size, is a fairly quiet volcano. An eruption would mean lahars and mud flows, but would not be an explosive eruption like Mt Saint Helens in 1980.

Whereas Mount Hood is an explosive volcano and an eruption would be as violent if not even more violent and destructive than Mt Saint Helens.

Is this correct? The 19th century Mt Rainier eruptions did little damage to the mountain(if any at all). Is there a reason to suspect a more vigorous eruption next time?

**Tags:** volcanology, volcanic-eruption

> **Comments:**
> **username_1**: You seem to be of the opinion that a lahar is not a major hazard.  Consider the fact that the city of Tacoma is built on top of debris from a 5000-year-old lahar.  

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## 2 answers

### Answer by username_3 on 2024-09-08. Score: 8

All the [Cascades](https://en.wikipedia.org/wiki/Cascade_Range) volcanoes are [andesite](https://en.wikipedia.org/wiki/Andesite) composite cone stratovolcanoes, which means that, among other things, they have highly variable eruptive chemistry and behaviour.

Saint Helens has the most recent history of violent eruption but all four major peaks have a explosive history. The massive size of St Helens 1980 wasn't because of the material erupted, i.e. not because St Helens is a particularly explosive volcano, but because of the [flank collapse](https://en.wikipedia.org/wiki/1980_eruption_of_Mount_St._Helens#Landslide_and_climactic_phase) that occurred when the mountain changed shape due to lava migration.

Andesite volcanoes are extremely unpredictable for example the last three eruptions from [Mount Tongariro](https://en.wikipedia.org/wiki/Mount_Tongariro) were a small ash eruption in 2012, a [basaltic](https://en.wikipedia.org/wiki/Basalt) low silica eruption that I frustratingly can't find the date for right now and a previous quite large ash eruption in the 1890s.

Rainer has a similar history of varying eruptions but with an even more violent [rhyolite](https://en.wikipedia.org/wiki/Rhyolite) phase though it has been far less active in recent history, with the last cone building eruptions ending ~1000 years ago and the last, small, eruption c.1450AD. The reason that [lahars](https://en.wikipedia.org/wiki/Lahar) are a possible outcome if Rainer erupts is that it has a history of explosive eruptions that have laid down thick ash layers on it's slopes. But Rainer may well be extinct, no longer being feed magma from the [subduction](https://en.wikipedia.org/wiki/Subduction) of the [Pacific Plate](https://en.wikipedia.org/wiki/Pacific_Plate) in which case no eruptive activity should be expected. If however Rainer ever does erupt again it's now highly eroded cone will probably be prone to slope collapse, Mount St Helens style, potentially resulting in a massively violent blast.

Mount Hood has never been quite as high in silica as Rainer, and thus has a less violent ancient history but as an andesite it is equally unpredictable and is also highly eroded making the cone fragile and prone to collapse if it erupts again.

In short none of the big four Cascade Volcanoes are anything I'd want in my backyard and of the two in the question neither is particularly safer than the other. You can't make any assumptions or estimates of future activity based on the history of andesite volcanoes because their chemistry is too prone to sudden change.

> **Comments:**
> **username_0**: If Mount Rainier were extinct, would there still be seismic activity directly underneath it(Earthquake swarms)? I live in the PNW so Mt Rainier is very much in my backyard...I just hope it doesn't blow up anytime soon as it will be sad to lose such a majestic mountain.  
> **username_3**: @MrX Maybe, it depends on the type and depth of the earthquakes in question and that depends on what *exactly* the plate boundary is doing at depth. What you wouldn't see is [harmonic tremor](https://en.wikipedia.org/wiki/Harmonic_tremor), that is specific to the movement of magma.  
> **username_4**: Purely out of curiosity, that would mean that Mount Mazama was also an andesite volcano before its collapse?  
> **username_3**: @username_4 Given it's description and the tectonic setting it certainly appears to have been, the eruption that led to it's collapse was very high silica, possibly a rhyolite chemistry but it's not unusual for an andesite to have a single episode with extremely high silica, or an episode with very little, that's what makes them *so* dangerously unpredictable.  
> **username_0**: One more question : I looked at data from the USGS about earthquake swarms on Mt Rainier and Mt Hood respectively. Mt Rainier shows a linear increase in seismic activity over the past 50 years whereas with Mt Hood there is an exponential increase in seismic activity. Does that mean anything? It doesn't say whether the quakes are harmonic tremors or not though.  
> **username_3**: @MrX 50 years is a lot for us, but it's the blink of an eye in [geological time](https://en.wikipedia.org/wiki/Geologic_time_scale), far less than the error bars on most dating techniques. We may realise that it was a significant thing in hindsight one day but for now we can't really point at it and say "that means this" as with many problems in geology we just don't have enough data over time to assess such slow moving processes.  

---

### Answer by username_2 on 2024-09-08. Score: 6

Here are some general considerations on the topic.

1/ Be careful when using the term "hazardous" or "hazard". In the field of natural disasters, like volcanic eruptions, hazard is used to describe a physical phenomenon that could be dangerous, or not, depending on the context. A lahar is a hazard, a pyroclastic flow is a hazard. Now that doesn't mean they present a *risk*, which is a whole different concept. Risk is usually defined as:

Risk = Hazard $\times$ Vulnerability

Which means that if the vulnerability is null, then the risk as well, even if the hazard is great. In volcanology, a good example of this is the [Novarupta](https://en.wikipedia.org/wiki/Novarupta) 1912 eruption: it was the largest explosive eruption of the 20th century (beating Pinatubo 1991, and dwarfing St Helens 1980), yet it occurred in a remote, unpopulated area, hence had no effects on human communities. The hazard was great, but there was zero vulnerability, thus zero risk.

2/ Be careful when comparing hazards between them. You seem to imply that a volcano doing "only" lahars would be less dangerous than a volcano that would do an explosive eruption, but it all depends on the local context (i.e., the exposure of local populations to those different kinds of hazards). Lahars can be quite deadly, as recently demonstrated at Marapi (Sumatra, Indonesia), with 67 victims on May 11, 2024 (not to mention the [Armero tragedy](https://en.wikipedia.org/wiki/Armero_tragedy)). In fact, lahars rank as the 4th deadliest volcanic hazards according to [Witham 2005](https://doi.org/10.1016/j.jvolgeores.2005.04.017) (you can see the table in [my answer](https://earthscience.stackexchange.com/a/24400/18081) to "Can people on the side of a volcano survive the eruption?"). It is true that pyroclastic flows rank 2nd.

I don't know the specifics of those two particular volcanoes, but in summary, keep in mind that it is not only a matter of volcanic hazards: the vulnerability is an important factor to consider. If there is a settlement in a valley that could serve as a lahar corridor during an eruption of Mount Rainier, then it could be more devastating that an eruption of Mount Hood. If Mount Hood collapses like St Helens did, then it depends on where human communities are. If you look at the [map of St Helens victims](https://www.columbian.com/news/2010/may/18/interactive-map-mount-st-helens-eruption-victims/), they were all North from the volcano; the eruption did not affect the southern side.


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