jmsbert
The extents of the lava stream have been updated about 4 hours ago (18.10.2021, 16:08). As written in the changeset [1] the drone imagery "perimetro_dron_18102021_11h" has been used [2]. As this imagery is updated almost everyday this imagery has become one of the main sources for the mapping.
The shape of the lava stream around your note fits very well to this drone imagery.
The water reservoirs here have been mapped about one week ago, e.g. way #992024201 [3] and fit to the imagery taken e.g. yesterday [4]. One water basin more in the north which had been mapped based on Grafcan imagery some weeks ago has been removed today as requested by note #2899666 as the drone imagery [2],[4] confirmed that it does not exist anymore. This was the only inaccuracy I can see here, but it is fixed. 

Altogether I do not agree with your complains about the mapping quality in OSM here. What is your reference data for the complain?
Remember to always press "CTRL" + "F5" to get the latest representation of the map as the rendering of the changes may take some time.
Please take a look at the comments the contributors write to their changesets (accessible via "chronic" button in OSM.

[1]: https://www.openstreetmap.org/changeset/112655062

[2]: https://datos-lapalma.opendata.arcgis.com/maps/1028079efceb4f9eb9f421ba5f47d37d/explore?location=28.625206%2C-17.926482%2C17.88
[3] https://www.openstreetmap.org/way/992024201

[4] https://www.opendatalapalma.es/maps/dron-fotogrametria-17102021-12h-fn/explore?location=28.624651%2C-17.926799%2C18.20