Damage to buildings

 

Here’s a very simple version of the detailed buildings damage table in the report by Baxter and his team:

 

                                                                                                                                            Dynamic pressure (kPa)

Level 0       No                           No significant blast damage.

                 damage                   Slight charring of wood.                                                                     Less than 1

 

Level 1       Light                        Few broken windows.

                 damage                   Some fire damage to roofs.                                                                      1-3

 

Level 2       Moderate                 Most windows and doors facing volcano blown out.

                 damage                   Roofs burned. Wooden houses wrecked. Some debris.                              2-6

 

Level 3       Severe                     Brick and stone house walls begin to fail. Likewise

                 damage                   weak reinforced concrete. Roofs lifted off. Abundant

                                               missiles make “drifts” where obstructed.                                                   4-10

 

Level 4       Partial                     Masonry houses wrecked. Obvious missile damage.

                 devastation                                                                                                                           8-25

 

Level 5       Total                       All but the strongest reinforced concrete buildings

                 devastation              wrecked and blown away. Little remains.                                            More than 25

 

 

Fig. 5  Surge damage to Dyer’s, Montserrat. Note extreme local variability of blast damage and also damage by fire (Maggie Mangan, USGS).

Fig. 6  Level 2 surge damage, Montserrat. Once the hot gas and ash gets in, fire does the rest (Copyright NERC).

Fig. 7  Level 2 surge damage, Trials, Montserrat. Note the unexploded gas cylinder. These were less inclined to explode than was expected before the surges happened (R. Roscoe).

 

 

 

Fig. 8  Aerial view of Level 3 surge damage to a sturdy house (Tar River Estate House): some trees toppled, roof mostly removed, masonry beginning to fail, debris scattered around (Copyright NERC). Notice that timber is charred in this view but not in the Merapi one beside. The "violence" of a surge is not the same as its temperature.

Fig. 9  Level 4 damage in a village below Merapi, Indonesia, after the November 2010 eruption. Close-up of smashed cinder blocks shows that the agents of demolition were not only the dense surge cloud but also flying tree trunks, house timbers etc.

C:\Users\Bob\Desktop\Merapi 2010\i32_25659933.jpg

 

 

 

Missiles

 

Whilst the dynamic pressure alone of a dense and fast-moving surge can wreck a house, the damage is made far worse by the ability of fast surges to pick up and throw missiles. This process becomes a noticeable source of damage around Level 2, when scattered debris is left lying around and walls facing the volcano are “sandblasted” by the small rocks and other rubble flying about. By Level 3 the flying junk includes galvanised roofing sheets and parts of trees – capable of delivering a vicious blow to a wall. By Level 5 even large boulders are dragged along at the base of the surge, destroying all in their way. This is why the remnants of reinforced concrete walls in St Patrick’s (Fig. 12) have holes in them where hit by flying boulders and look like the target area of a monstrous bowling alley, used by the mythical Norse family Odin, Thor, Magni and Modi in one of their more violent contests with the Berserks. Baxter and his team comment that extensive damage from missile strikes makes it well nigh impossible to disentangle this type of damage to buildings from the simple “pushing power” of the surge.

 

 

Fig. 10  Aerial views of part of St Patrick’s and Morris’, Montserrat, swept away by a very violent surge on Boxing Day 1997 (Copyright NERC).

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Fig. 11  Level 4 damage. House in Gingoes-Trials, Montserrat partly wrecked by a flying tree rootstock that is just visible inside the ruin (Copyright NERC).

Fig. 12.  Level 5 damage. The remains of a wrecked reinforced concrete house in Trials. Note holes in the remaining concrete wall made by flying boulders (Copyright NERC).

Fig. 13  Level 5 damage. Reinforced concrete mostly swept away by an intense surge, Francisco Leon, El Chichon, Mexico 1982 (Bob Tilling, USGS)

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